Medical Biochemistry Tips (3): Enzymes (Amylase, CK, ALP, LDH, GGT)

         

Dr. James Manos (MD)

January 5, 2016

    

      Review: Tips in Medical Biochemistry

            Volume (3)

CONTENTS

METABOLIC DISTURBANCES – ENZYMES

Amylase

Hyperamylasemia – causes

Creatine Kinase (CK)

Rhabdomyolysis

Rhabdomyolysis workup

Alkaline phosphatase 

Lactate dehydrogenase (LDH)

Gamma-glutamyltransferase (GGT)

 METABOLIC DISTURBANCES – Enzymes

      Amylase

·         Hyperamylasemia (increased blood serum amylase) – causes:

·         a) Pancreatic diseases (P-type - isoamylase): acute pancreatitis (lipase is more specific), chronic pancreatitis, pancreatic pseudocysts, pancreatic trauma [blunt trauma, abdominal or retroperitoneal surgery, ERCP (a 3- to 4-times increase in serum amylase levels 4 hours after ERCP predicts the occurrence of complicating postprocedure pancreatitis)], choledocholithiasis (in patients presenting with biliary-type abdominal pain, a 3-fold increase in serum amylase levels that returns to normal within 48-72 hours suggests stone passage through the common bile duct), pancreatic ascites.

·         Note: In acute pancreatitis, serum amylase is usually elevated 3-fold and then returns to normal by 3 – 7 days. Patients with pancreatitis associated with hypertriglyceridemia or those with significant acinar cell injury due to previous episodes of pancreatitis or chronic pancreatitis may not exhibit hyperamylasemia.

·         b) Salivary diseases:  parotitis (S type - isoamylase) (trauma, surgery to the salivary gland, calculi of the salivary duct, radiation of the neck that causes duct obstruction, mumps), chronic alcoholism (salivary amylase levels are 3 times higher than normal in 10% of patients with alcoholism; this may be related to chronic liver disease). According to a study, saliva amylase is collated with sleep problems.

·         c) Decreased metabolic clearance: renal failure & liver disease (hepatitis or cirrhosis) result in increased S-type and P-type isoamylases.

·         d) Intestinal disorders: Gut diseases, including mucosal inflammatory disease of the small intestine, strangulation ileus, mesenteric ischemia/ mesenteric infarction, intestinal obstruction, appendicitis, and peritonitis, usually result in increased P-type isoamylase. Gut perforation and a perforated peptic ulcer can also result in hyperamylasemia.

·         e) Female reproductive tract diseases: Ruptured ectopic pregnancy, fallopian or ovarian cysts, torsion of an ovarian cyst, and salpingitis can result in increased S-type isoamylase.

·         f) Misc: ectopic amylase production by lung, ovary, pancreas, and colon malignancies; pheochromocytoma; thymoma; multiple myeloma (increased salivary amylase); and breast cancer (increased pancreatic amylase); ketoacidosis; non-ketotic acidosis; postoperatively (e.g. extracorporeal circulation or non-abdominal surgery); systemic lupus erythematosus (SLE); ciprofloxacin treatment; pneumonia (increased salivary amylase); cerebral trauma; burns; abdominal aortic aneurysms (increased pancreatic amylase); drugs (increased salivary and/or pancreatic amylase); anorexia nervosa and bulimia (increased salivary amylase); non-pathological (increased salivary and/or pancreatic amylase); organophosphate poisoning; and macro-amylasemia (a benign condition in which the amylase molecule binds with a large complex molecule (e.g., immunoglobulin, polysaccharide), thereby prolonging its half-life and decreasing renal clearance; about 2 –  5% of patients with hyperamylasemia have macro-amylasemia).

·         Amylase may also be measured in other blood fluids including urine & peritoneal fluid.

·         Creatine Kinase (CK): CK is an enzyme found in the mitochondria and cytoplasm of skeletal muscle (predominantly), cardiac muscle, brain, and other visceral tissues. Its primary function is in the generation and facilitation of transportation of high-energy phosphates. CK is a dimeric molecule, composed of M and B subunits. The 2 subunits can form 3 isozymes: CK-MM, CK-MB, and CK-BB. Skeletal muscle, myocardium, and neuronal tissue are the primary sources of CK-MM, CK-MB, and CK-BB, respectively.  

·         I) Low CK – causes:

·         Muscle disease: reduced muscle mass (end-stage disease); corticosteroid treatment; myosin loss (especially weeks after onset); dermatomyositis, childhood type (some patients); hyperthyroidism; multiorgan failure; rheumatic diseases (active inflammation); rheumatoid arthritis (RA); systemic lupus erythematosus (SLE); spondyloarthropathies; fasciitis; muscle disorders.
     Additionally, a case study relates low levels of CK with breast cancer. 

·         Also, a low CK level may be seen in early pregnancy.

·         Reduced CK-BB can be seen with Huntington's disease, multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS).

·         II) High CK – causes: increased CK is predominantly used to diagnose neuromuscular diseases and acute myocardial infarction.

·         a) Neuromuscular disorders include myopathies, muscular dystrophy, rhabdomyolysis (may have CK levels that are as much as 100 times normal levels) drug-induced myopathies, neuroleptic malignant syndrome, malignant hyperthermia, and periodic paralysis. Also, people with Kennedy disease, a rare genetic neuromuscular disorder, may have elevated CK in their blood.

·         b) Because the primary source of CK-MB is myocardium, an elevated CK-MB level reflects myocardial injury, including acute myocardial infarction, myocarditis, cardiac trauma, cardiac surgery, and endomyocardial biopsy. However, CK-MB makes up 5 – 7% of CK in skeletal muscle. Therefore, skeletal muscle injury can sometimes cause elevated CK-MB levels, leading to misinterpretation. Also, a recent study shows that CK-MB is related to high blood pressure (as elevated ATP (adenosine triphosphate) in the endothelium can cause vasoconstriction and antagonize nitric mediated vasodilatation). 

·         c) CK can also be raised in the absence of neuromuscular diseases or cardiac injury, such as after strenuous exercise, intramuscular (IM) injection, and with renal disease.

       d) Importantly, increased levels of CK, with normal CK-MB, may indicate some forms of cancers such as small cell lung cancer (SCLC) or primary hepatocellular (liver cell) carcinoma (HCC). LDH may initially be normal, and CK slightly raised above the normal upper range.  In SCLC the common tumor markers may not help (the tumor markers that are more specific are chromogranin A (CgA), pro-gastrin-releasing peptide (ProGRP), neuron-specific enolase (NSE), and CYFRA 21-1), while in HCC the tumor marker alpha-fetoprotein will be elevated. 

·         People who have greater muscle mass have higher CK levels than those who don't; for this reason, men generally tend to have higher values than women.

·         Many cases of hypothyroidism are associated with mild elevations in creatinine kinase (CK) and liver enzymes in the blood. They typically return to normal when hypothyroidism has been adequately treated.

·         Moderately increased CK levels may be seen following strenuous exercises such as in weightlifting, contact sports, or prolonged exercise sessions.

·         The clinical application of CK-BB is still limited. The elevated CK-BB in cerebrospinal fluid is a useful predictor of hypoxic brain injury after cardiac arrest.

·          III) CK unexpectedly High (the following causes are non – cardiac and emphasize more to neuromuscular and metabolic disturbances; cardiac causes should be suspected by assessing CK – MB):

·         1) asymptomatic high CK:  generally is more common in males than females; may occur at all ages. If high CK persists after rest, evaluation usually includes EMG (electromyography) and Muscle biopsy.

·         2) High CK with few, no, or atypical symptoms – Causes:

·         a) Endocrine: hypothyroidism or hypoparathyroidism.

·         b) Exercise: acute & producing muscle hypertrophy.

·    c) Muscle Trauma: injections (especially phenothiazines); psychosis; falls. Note: an EMG virtually never elevates a normal CK to abnormal levels.

·         d) Myopathies (asymptomatic):

·         i) Dystrophy: dystrophinopathy; limb-girdle muscular dystrophy (LGMD; 1C, 2A, 2B, 2P).

·         ii) Metabolic: glycogen storage disorders; CPT2 deficiency; AMPDA deficiency.

·   iii) Other hereditary myopathies: central core, Danon, distal; malignant hyperthermia; mitochondrial disease; myofibrillar myopathy; myopathy with tubular aggregates; myotonia (congenital; DM2 (Myotonic Dystrophy 1)); rippling muscle syndromes. 

·         e) Acquired disorders: inflammatory; drug toxicity.

·         f) Denervation: motor neuron diseases; small fiber polyneuropathies; not: Sensory-Motor polyneuropathies.

·         g) Idiopathic:

·         i) Hereditary Idiopathic.

·         ii) Other Idiopathic (50% to 80% of HyperCKemia): normal muscle: 30%; non-specific muscle abnormalities: 30%.

·         Rhabdomyolysis is the rapid breakdown of muscle tissue. This condition can be caused by severe physical, chemical, or biological injury to muscles.

·         Examples of causes include trauma, crushing injuries (e.g., car accidents, disasters such as earthquakes); high-voltage electrical shock; severe burns; thrombosis (blood clot) that blocks blood flow; toxins (e.g., heavy metals, snake venom, CO (carbon monoxide)); infections (e.g., HIV, Streptococcus, influenza; more common cause in children than adults); inherited genetic and metabolic disorders that affect muscles' ability to get or use energy; diseases such as muscular dystrophy and underlying conditions such as uncontrolled diabetes, hypothyroidism, and hyperthyroidism; several drugs including drugs of abuse (such as ethanol, heroin, cocaine and amphetamines such as ecstasy), amphotericin B, ampicillin, anesthetics, antidepressants, antihistamines, corticosteroids, lidocaine, lithium, protease inhibitors, quinine, salicylates, statins (taken to lower cholesterol levels), and theophylline (for asthma).

·         Complications: complications can result from the rapid release of cell contents into the blood. This has been known to cause damage to kidneys (acute kidney injury, AKI) and DIC (disseminated intravascular coagulation).

·         Treatment: Once diagnosed and depending on the extent of injury, a person with rhabdomyolysis may be treated with intravenous fluids  (usually isotonic saline 0.9%), +_ mannitol, furosemide, urine alkalization with sodium bicarbonate; treatment of hyperkalemia, and other supportive care as well as procedures used to protect organs (e.g., dialysis to prevent/limit kidney damage).

·         Rhabdomyolysis workup:  Useful laboratory tests include: complete blood count (CBC/ FBC; including hemoglobin, hematocrit, and platelets); serum chemistries, including blood urea nitrogen (BUN), creatinine, glucose, calcium, potassium, phosphate, uric acid, and liver function tests (LFTs); prothrombin time (PT); activated partial thromboplastin time (aPTT) (thromboplastin released from injured myocytes can cause disseminated intravascular coagulation (DIC)); serum aldolase; lactate dehydrogenase (LDH).

·         Metabolic disturbances:

·         a) Hyperkalemia, an immediate threat to life in the hours immediately after the injury, occurs in 10  –40% of cases. Liberated potassium can cause life-threatening dysrhythmias and death.

·         b) Hyperphosphatemia: does not require specific therapy.

·         c) Hypocalcemia: occurs early in the course of rhabdomyolysis. However, supplemental calcium is not recommended.

·         d) Hyperuricemia: increased purine metabolism causes hyperuricemia, however specific therapy with uricosuric agents or allopurinol is not indicated.

·         e) The BUN-creatinine ratio may be decreased because of the conversion of liberated muscle creatine to creatinine.

·         In an emergency department (ED)-based study of 97 adults with rhabdomyolysis, no patient presenting in an ED (emergency department) setting with an initial creatinine level of less than 1.7 mg/dL developed ARF (acute renal failure).

·         One series of 109 ED patients with rhabdomyolysis found that 50% had an elevated cardiac troponin I level. Of these, 58% were ultimately found (from electrocardiography (ECG) and echocardiography) to be true positives, 33% were false positives, and 9% were indeterminate.

·         Creatine kinase (CK) levels estimation: the most reliable and sensitive indicator of muscle injury is creatine kinase (CK). Assessing CK levels is most useful because of its ease of detection in serum and its presence in serum immediately after muscle injury. CK levels rise within 12 hours of muscle injury, peak in 24 – 36 hours, and decrease at a rate of 30 – 40% per day.  The serum half-life of CK is approximately 36 hours. CK levels decline 3 – 5 days after resolution of muscle injury; failure of CK levels to decrease suggests ongoing muscle injury or development of a compartment syndrome. The peak CK level, especially when it is higher than 15,000 U/L, may be predictive of renal failure. Total CK elevation is a sensitive but nonspecific marker for rhabdomyolysis. CK levels 5 times the reference range suggest rhabdomyolysis, though CK levels in rhabdomyolysis are frequently as high as 100 times the reference range or even higher. Serum CK levels more than 2 – 3 times the reference range and risk factors for rhabdomyolysis should make the doctor suspect early rhabdomyolysis; a full laboratory workup should be initiated. Because the total CK may increase from the initial values, CK levels should be repeated every 6 – 12 hours until a peak level is established.

·         Urine myoglobin levels estimation: a urine myoglobin assay is helpful in patients with coexisting hematuria (confirmed with microscopic examination) when the presence of myoglobin is suspected. A urine dipstick test for blood that has positive findings in the absence of red blood cells (RBCs) suggests myoglobinuria. Myoglobinuria may be sporadic or resolve early in the course of rhabdomyolysis. Urine dipstick findings are positive in fewer than 50% of patients with rhabdomyolysis; thus, a normal test result does not rule out this condition. Myoglobin has a short half-life and is, therefore, less useful as a diagnostic test in the later stages. Its detection in blood or urine is associated with a higher risk of renal impairment. However, it lacks specificity.

·         Αlkaline phosphatase (ALP, ALKP, ALPase, Alk Phos; also called basic phosphatase): is a hydrolase enzyme responsible for removing phosphate groups by dephosphorylation from many types of molecules, including nucleotides, proteins, and alkaloids. It is most effective in an alkaline environment. In humans, alkaline phosphatase is present in all tissues throughout the entire body but is mainly concentrated in the liver, bile duct, kidney, bone, intestinal mucosa, and placenta.

·         Humans and most other mammals contain the following alkaline phosphatase isozymes: ALPI (intestinal; molecular weight 150 kDa); ALPL (tissue-nonspecific; found on liver/bone/kidney); ALPP (placental; Regan isozyme). 

·         Diagnostic value of ALP:  normal ALP levels in adults are approximately 20 to 140 IU/L; though levels are significantly higher in children and pregnant women. Blood tests should always be interpreted using the reference range from the laboratory that performed the test.

·         High ALP levels can occur on bile duct obstruction. Also, ALP increases if there is active bone formation occurring (as ALP is a byproduct of osteoblast activity) such as the Paget’s disease.

·         Levels are also elevated in people with an untreated celiac disease.

·         Lowered levels of ALP are less common than elevated levels.

·         The source of elevated ALP levels can be deduced by obtaining serum levels of gamma-glutamyltransferase (GGT). Concomitant increases of ALP and GGT should raise the suspicion of hepatobiliary disease.

·         If bilirubin, AST & ALT are also elevated the increasing ALP is coming from the liver.

·         If GGT or 5’ – nucleotidase is also increased then the high ALP is likely due to liver disease.

·         If these two tests are normal, then high ALP is likely due to a bone condition.

·         If calcium & phosphorus are abnormal, usually the ALP is coming from the bone.

·         Children and adolescents normally have higher ALP levels than adults because their bones are growing, and ALP is often very high during a growth spurt, which occurs at different ages in boys and girls.  Also, postmenopausal women have higher ALP levels than women who still have menstrual cycles.

·         Causes of reduced ALP:   people with malnutrition such as celiac disease; lack of nutrients in the diet such as scurvy; hypophosphatasia (*1); patients with Wilson’s disease (an autosomal recessive genetic disorder in which copper accumulates in tissues; it manifests as neurological/ psychiatric symptoms & liver disease); postmenopausal women receiving estrogen therapy for osteoporosis; women taking oral contraceptives; children with achondroplasia & cretinism; children after a severe episode of enteritis; men with recent heart surgery, malnutrition, magnesium deficiency, hypothyroidism, or severe anemia; patients with pernicious anemia (*2) or aplastic anemia; and patients with chronic myelogenous leukemia (CML). 

·         Causes of elevated ALP: 

·         a) Liver disease (Liver ALP): cholestasis/  blockage of the bile ducts (obstructive jaundice), cholecystitis, gallstones, cholangitis, cirrhosis, primary biliary cirrhosis, fatty liver, sarcoidosis, liver cancer, gallbladder cancer, cholangiocarcinoma, liver metastases, drug intoxication, hepatitis, medications [verapamil (a calcium channel blocker used for hypertension, angina pectoris and cardiac arrhythmia), carbamazepine & phenytoin (the last 2 are used as antiepileptics), erythromycin (antibiotic), allopurinol (for elevated uric acid), ranitidine (a histamine H2 – receptor antagonist that inhibits stomach acid production – commonly used on peptic ulcer disease and gastroesophageal reflux disease)] .

·         b) Bone disease (Bone ALP): Paget’s disease of the bones (*3), osteosarcoma (a bone cancer), bone metastases of prostatic cancer (ALP may be very high); other bone metastases (e.g. breast cancer), renal osteodystrophy (*4), bone fractures, multiple myeloma (associated with bone lesions/ fractures); skeletal involvement of other primary diseases such as osteomalacia (*5), rickets, normal healing of a bone fracture, hyperparathyroidism, vitamin D deficiency (moderate rise), malignant tumors (ALP originating from the tumor), renal disease (with secondary hyperparathyroidism), primary hypothyroidism.

·         Also, other unlisted musculoskeletal conditions may also cause elevated alkaline phosphatase. ALP as carcino-placental alkaline phosphatase (Reagan's isoenzyme) is elevated in breast carcinoma, colon cancer, and Hodgkin’s lymphoma.

·         Other causes include: pregnancy (especially 3^rd trimester; the placenta makes ALP), myocardial infarction, infectious mononucleosis, sepsis, kidney cancer, pregnancy, Hodgkin’s lymphoma, congestive heart failure (CHF), malnutrition/ protein deficiency, zinc deficiency, temporarily after blood transfusions or heart bypass surgery; on healing fractures, certain bacterial infections, lung cancer, chlorpropamide therapy (an antidiabetic), infectious mononucleosis, pancreatic cancer, primary sclerosing cholangitis, polycythemia vera, myelofibrosis, leukemoid reaction to infection, women using hormonal contraception, pregnancy, herpes zoster (Shingles), rickets/ Vitamin D deficiency, amyloidosis, granulation tissue, GI (gastrointestinal) inflammation [inflammatory bowel disease (IBD; including Crohn’s disease and ulcerative colitis), ulcers], rheumatoid arthritis (RA), hyperthyroidism,transient hyperphosphatasemia of infancy (benign; often associated with infection), seminoma (a germ cell tumor of the testicle or rarely on extragonadal locations such as the mediastinum), celiac disease, sarcoidosis, syphilis, lymphoma.   
                                      

·   (*1) Hypophosphatasia is an autosomal recessive disease; a metabolic bone disease; tissue non – specific ALP (TNSALP) deficiency in osteoblasts and chondrocytes impairs bone mineralization, leading to rickets (on children) or osteomalacia (on adults). It is characterized by subnormal serum activity of the TNSALP enzyme. 
          

·         (*2) Pernicious anemia is one of many types of megaloblastic anemias. It may occur because of loss of the gastric parietal cells which are responsible, in part, for the secretion of intrinsic factor, a protein essential for subsequent absorption of vitamin B12 in the ileum. Antibodies to intrinsic factor and parietal cells cause the destruction of the oxyntic gastric mucosa, in which the parietal cells are located, leading to the subsequent loss of intrinsic factor (IF) synthesis. The loss of ability to absorb vitamin B12 is the most common cause of adult vitamin B12 deficiency.               

·       (*3) Paget's disease of bone is a chronic disorder (more common in the elderly) that can result in enlarged and misshapen bones. It is caused by the excessive breakdown and formation of bone, followed by disorganized bone remodeling. This causes affected bone to weaken, resulting in pain, misshapen bones, fractures, and arthritis in the joints near the affected bones. Rarely, it can develop into a primary bone cancer known as Paget's sarcoma. Often Paget's disease is localized to only a few bones in the body. The pelvis, femur, and lower lumbar vertebrae are the most commonly affected bones.     
 

·        (*4) Renal osteodystrophy or chronic kidney disease-mineral and bone disorder (CKD-MBD) is a bone disease characterized by bone mineralization deficiency, that is a direct result of the electrolyte and endocrine derangements that accompany chronic kidney disease (CKD). Renal osteodystrophy can be further divided into metabolic states associated with either high or low bone turnover. It is usually diagnosed after treatment for end-stage renal disease begins. Blood tests will indicate decreased calcium and calcitriol (1,25-dihydroxy vitamin D3) and increased phosphate & parathyroid hormone (PTH). X-rays will show bone features of renal osteodystrophy (chondrocalcinosis at the knees and pubic symphysis, osteopenia and bone fractures), but may be difficult to differentiate from other conditions.  

· (*5) Osteomalacia is the softening of the bones caused by defective bone mineralization secondary to inadequate levels of available phosphate & calcium, or because of overactive resorption of calcium from the bone which can be caused by hyperparathyroidism (that causes hypercalcemia). Osteomalacia in children is known as rickets. Thus, the use of the term "osteomalacia" is often restricted to the milder, adult form of the disease. Signs and symptoms can include diffuse body pains, muscle weakness, and fragility of the bones. The most common cause of osteomalacia is a deficiency of vitamin D (which is normally derived from sunlight exposure and, to a lesser extent, from the diet).

·         Lactate dehydrogenase (LDH):  is an enzyme found in nearly all living cells (animals, plants, and prokaryotes). It catalyzes the conversion of pyruvate to lactate and back, as it converts NAD to NAD⁺ and reversely.

·         A Dehydrogenase is an enzyme that transfers a hydride from one molecule to another. LDH exists in four distinct enzyme classes. Here the common NAD(P)-dependent L-lactate dehydrogenase is mentioned. Other LDHs act on D-lactate and/or are dependent on cytochrome C are D – lactate dehydrogenase (cytochrome) and L-lactate (L – lactate dehydrogenase (cytochrome).

·          LDH is found extensively in body tissues, such as blood cells and heart muscle. Because it is released during tissue damage, it is a marker of common injuries and diseases.

·         Causes of elevated LDH:  

·         a) Cancer. LDH is involved in tumor initiation and metabolism. Cancer cells rely on anaerobic respiration for the conversion of glucose to lactate even under oxygen-sufficient conditions (Warburg effect). This state of fermentative glycolysis is catalyzed by the A form of LDH. This mechanism allows tumorous cells to convert the majority of their glucose stores into lactate regardless of oxygen availability, shifting use of glucose metabolites from simple energy production to the promotion of accelerated cell growth and replication. While recent studies have shown that LDH activity is not necessarily an indicator of metastatic risk, LDH expression can act as a general marker in the prognosis of cancers. Expression of LDH5 and VEGF in tumors and the stroma has been found to be a strong prognostic factor for diffuse or mixed-type gastric cancers. 

·         b) Hemolysis. LDH is often used as a marker of tissue breakdown as LDH is abundant in red blood cells (RBCs) and can function as a marker for hemolysis. Hemolysis is the premature destruction of erythrocytes. Hemolytic anemia will develop if bone marrow activity cannot compensate for the erythrocyte loss. The severity of the anemia depends on whether the onset of hemolysis is gradual or abrupt and on the extent of erythrocyte destruction. Mild hemolysis can be asymptomatic while the anemia in severe hemolysis can be life-threatening and cause angina and cardiopulmonary decompensation. Serum LDH elevation is a criterion for hemolysis. LDH elevation is sensitive for hemolysis, but is not specific, since LDH is ubiquitous and can be released from neoplastic cells, the liver, or from other damaged organs. Although an increase in LDH isozymes 1 and 2 is more specific for red blood cell destruction, these enzymes are also increased in patients with myocardial infarction.

·         A blood sample that has been mishandled can show false-positively high levels of LDH due to erythrocyte damage (hemolyzed blood sample).

·         c) Myocardial infarction (heart attack):  levels of LDH peak at 3 – 4 days and remain elevated for up to 10 days. In this way, elevated levels of LDH (where the level of LDH1 is higher than that of LDH2, i.e., the LDH Flip, as normally, in serum, LDH2 is higher than LDH1) can be useful for determining whether a patient has had a myocardial infarction if they come to doctors several days after an episode of chest pain. LDH is not as specific as troponin. While increases in serum LDH also are seen following a myocardial infarction, the test has been replaced by the determination of troponin.

·         d) Tissue turnover. Other uses are an assessment of tissue breakdown in general (this is possible when there are no other indicators of hemolysis). It is used to follow-up cancer patients (especially on lymphoma), as cancer cells have a high rate of turnover with destroyed cells leading to an elevated LDH activity.

·         e) Dysgerminoma. Elevated LDH is often the first clinical sign of dysgerminoma, a rare malignant cell tumor. Not all dysgerminomas produce LDH, and this is often a non-specific finding.

·         f) Pneumocystis jiroveci pneumonia (PCP) & histoplasmosis on HIV (+) patients.  LDH is often measured in HIV patients as a non-specific marker for Pneumocystis jiroveci pneumonia (PCP). Elevated LDH in the setting of upper respiratory symptoms in an HIV patient suggests but is not diagnostic for PCP. In a study on HIV (+) patients with respiratory symptoms, a very high LDH level (>600 IU/L) indicated histoplasmosis.

·         g) Other causes: sepsis, acute muscle injury, pancreatitis, bone fractures, lymphoma. intestinal infarction, megaloblastic anemia, pernicious anemia, Hodgkin's disease, abdominal and lung cancers, severe shock, and hypoxia, pulmonary infarction, pulmonary embolism, leukemia, infectious mononucleosis, progressive muscular dystrophy, liver disease, and renal disease. Strenuous exercise can cause temporary elevations in LDH. 

·         Causes of falsely elevated levels:

·         i) Thrombocytosis. If a person's platelet count is increased, serum LDH can be artificially high and not reflective of the LDH actually present in the circulation.

·         ii) Elevation of LDH on a hemolyzed specimen (in vitro hemolysis): red blood cells contain much more LDH than serum. A hemolyzed sample is not acceptable. LDH activity is one of the most sensitive indicators of in vitro hemolysis. Causes can include transportation via pneumatic tube, vigorous mixing, or traumatic venipuncture. Hemolysis of a blood specimen may happen if the specimen is handled roughly, stored in extreme temperatures, or if the sample was difficult to collect.

·         Causes of marked elevations in LDH: megaloblastic anemia, untreated pernicious anemia, Hodgkin's disease, abdominal and lung cancers, severe shock, and hypoxia.

·         Causes of moderate to slight increases in LDH:  myocardial infarction (MI), pulmonary infarction, pulmonary embolism, leukemia, hemolytic anemia, infectious mononucleosis, progressive muscular dystrophy (especially in the early and middle stages of the disease), liver disease, and renal disease.

·         In liver disease, elevations of LDΗ are not as significant as the increases in aspartate aminotransferase (AST) and alanine aminotransferase (ALT).

·         Increased levels of the enzyme are found in about 1/3 of patients with renal disease, especially those with tubular necrosis or pyelonephritis. However, these elevations do not correlate well with proteinuria or other parameters of kidney disease.

·         Occasionally, a raised LD level may be the only evidence to suggest the presence of a hidden pulmonary embolus.

·         Body fluids Exudates & transudates: measuring LDH in fluid aspirated from a pleural (or pericardial) effusion can help in the distinction between exudates (actively secreted fluid, e.g., due to inflammation) or transudates (passively secreted fluid, due to high hydrostatic pressure or low oncotic pressure). The usual criterion is that a ratio of fluid LDH versus the upper limit of normal serum LDH of more than 0.6 or 2/3 indicates an exudate, while a rate of less suggests a transudate. In empyema (collection of pus in the pleural cavity) the LDH levels, in general, will exceed 1,000 IU/L.

·         Meningitis/ meningoencephalitis: high levels of LDH in CSF (cerebrospinal fluid) are often associated with bacterial meningitis. In the case of viral meningitis, elevated LDH, in general, indicates the presence of encephalitis and poor prognosis.

·         Gamma – Glutamyl transferase (GGT): is an enzyme found in cell membranes of many tissues mainly in the liver, kidney (proximal renal tube), and pancreas. It is also found in other tissues including the intestine, spleen, heart, brain, and seminal vesicles. The highest concentration is in the kidney, but the liver is considered the source of regular enzyme activity. The reference range for gamma-glutamyl transferase (GGT) is 0 – 30 IU/L, however individual test results should always be interpreted using the reference range from the laboratory that performed the test. In most studies, males and females have equal levels, although some studies have shown 25% higher GGT in men compared with women.

·         Levels of GGT increase with age in women, but not in men, and are always somewhat higher in men than in women.

·         Infants have 6 – 7 times the upper limit of the adult reference range, which declines to adult levels around age 7 months.  

·         GGT levels are within the reference range for bone disorders, pregnancy, and muscle disease.

·         GGT levels are usually normal in myocardial infarction (MI, heart attack); however, they can increase approximately 4 days after MI. 

·         The GGT test may be used to determine the cause of elevated alkaline phosphatase (ALP).

·         Both ALP and GGT are elevated in disease of the bile ducts and in some liver diseases, but only ALP will be raised in bone disease. Therefore, if the GGT level is normal in a person with a high ALP, the cause of the elevated ALP is more likely a bone disease. The GGT test is sometimes used to help detect liver disease and bile duct obstructions. It is usually ordered in conjunction with or as a follow-up to other liver tests such as ALT, AST, ALP, and bilirubin.

·         In general, an increased GGT level indicates that a person's liver is being damaged but does not explicitly point to a condition that may be causing the injury.

·         GGT can be used to screen for chronic alcohol abuse and to monitor for alcohol use and/or abuse in people who are receiving treatment for alcoholism or alcoholic hepatitis. 

·         Causes of increased GGT levels:

·         a) GGT levels are increased in patients with liver diseases in general, including hepatitis (acute and chronic), liver cirrhosis, liver cancer & metastasis, cholestasis, alcoholic liver disease, primary biliary cirrhosis & sclerosing cholangitis.

·         b) Extrahepatic causes for GGT level elevation include pancreatitis, diabetes mellitus, prostate cancer, breast & lung cancer, systemic lupus erythematosus (SLE), and congestive heart failure (CHF).

·         c) Chronic coronary artery disease (CAD). The level of elevation correlates with the risk of death secondary to cardiovascular disease. GGT, in fact, accumulates in atherosclerotic plaques suggesting a potential role in the pathogenesis of cardiovascular diseases. Elevated GGT levels may be an indicator of cardiovascular disease and/ or hypertension. Some studies have shown that people with increased GGT levels have a high risk of dying from heart disease, but the reason for this association is not yet known.

·         d) Medications: such as barbiturates (e.g. phenobarbital), carbamazepine, cimetidine, furosemide, heparin, isotretinoin, methotrexate, oral contraceptives, phenytoin, aspirin, some NSAIDs (non – steroidal anti-inflammatory drugs), valproic acid,  lipid-lowering drugs, antibiotics, histamine receptor blockers (used to treat excess stomach acid production), antifungal agents, antidepressants, and hormones such as testosterone. 

·         e) Herbs: e.g., Kava, Black Cohosh, Boswellia Serrata, and St John’s wort.

·         f) Smoking.

·         g) Alcoholism.  GGT will be elevated in about 75% of chronic alcohol drinkers. Isolated elevation or disproportionate elevation compared to other liver enzymes (such as ALP or ALT) can indicate alcohol abuse or alcoholic liver disease, and can mean excess alcohol consumption up to 3 or 4 weeks before the test. Even small amounts of alcohol within 24 hours of a GGT test may cause a temporary increase in the GGT.  

·         h) Black people. GGT levels are higher among blacks.

·         i) Infants have 6 – 7 times the upper limit of the adult reference range, which declines to adult levels around age 7 months.

·         j) Mononucleosis-like syndrome (MLS).

·         Note: high body mass index (BMI) is associated with diabetes mellitus type 2 only in persons with high serum GGT.   

·         Causes of decreased GGT levels:

·         a) Hypothyroidism.

·         b) Early pregnancy.

·         c) Clofibrate and oral contraceptives can decrease GGT levels.