Clinical Enzymes Quiz

Alkaline Phosphate/Alkaline Orthophosphoric Monoester Phosphohydrolase

• Bone isoenzyme increases with osteoblastic activity, elevated in children and adults over 50.
• Intestinal ALP presence depends on blood type (secretor gene and H substance). B or O blood group increases after a fatty meal.
• Elevated in bone disorders like Paget's disease (osteitis deformans) and dialysis patients.
• Carcinoplacental ALP is found in cancers (lung, breast, ovarian, gynecological) and is heat-stable.
• Nagao ALP is a variant, inhibited by L-leucine and phenylalanine, found in certain cancers.

Methods for ALP Analysis

• Heat Fractionation/Stability Test: Placental is heat-stable, bone is heat-labile.
• Chemical Inhibition Test: Phenylalanine inhibits placental and intestinal ALP, urea inhibits bone ALP, and levamisole inhibits liver and bone ALP.
• Bowers and McComb (Szasz modification) is considered the most specific method.

Decreased ALP

• Zinc deficiency

Increased ALP

• Osteitis deformans
• Obstructive jaundice

Acid Phosphatase/ Acid Orthophosphoric Monoester Phosphohydrolase

• Catalyzes the same reaction as ALP but is active at pH 5.0.
• ACP activity >50 IU/L indicates seminal fluid in the sample.
• Used for detecting prostatic adenocarcinoma.
• Helpful in forensic cases (rape investigations).
• Thymolphthalein monophosphate is a specific substrate.
• Must be free from hemolysis.

Increased ACP (with Metastatic Bone Involvement)

• Prostatic carcinoma
• Breast, lung, and thyroid carcinoma
• Gaucher's disease
• Niemann Pick Disease

Aspartate Aminotransferase (AST)

• Two isoenzyme fractions (cytoplasm and mitochondrial AST).
• Cytoplasmic isoenzyme is predominant in serum.
• Found in cardiac tissue, liver, and skeletal muscle.
• Useful in evaluating myocardial infarction, hepatocellular disorders, and skeletal muscle involvement.

Alanine Aminotransferase (ALT)

• Similar enzymatic activity to AST
• High concentration in the liver.
• More liver-specific than AST.
• Very significant in evaluating hepatic disorders.
• More sensitive and specific for post-transfusion hepatitis and occupational toxic exposures than AST.
• Requires pyridoxal phosphate (vitamin B6) as a coenzyme.
• Hemolysis should be avoided; heparin may inhibit some AST methods.

Increased Transferases

• Toxic hepatitis
• Acute myocardial infarction
• Wolff-Parkinson White Syndrome
• Trichinosis
• Chronic alcoholism
• Dermatomyositis
• Reye's syndrome
• Viral hepatitis
• Muscular dystrophy
• Acute pancreatitis

Amylase/Alpha-1-4 Glucan-4-glucohydrolase (AMS)

• Catalyzes starch and glycogen breakdown, important in starch digestion.
• Smallest enzyme (50,000-55,000 daltons)
• Earliest pancreatic marker
• Isoenzymes: S-type (ptyalin) and P-type (amylopsin) found in normal serum.

Methods for Amylase analysis

• Saccharogenic: Classic method, measures reducing sugars produced by starch hydrolysis.
• Amyloclastic: Measures amylase activity by following substrate concentration decrease.
• Chromogenic: Measures amylase activity via color change from substrate dye reaction.
• Coupled-enzyme: Measures amylase activity via continuous monitoring.

Increased Serum Amylase

• Acute pancreatitis
• Ectopic pregnancy
• Peptic ulcers
• Alcoholism
• Mumps-parotitis

Lipase (LPS)/Triacylglycerol Acylhydrolase

• Plasma concentrations typically normal in salivary gland involvement.
• Major tissue source is the pancreas.

Lactate Dehydrogenase (LD)

• Hydrogen-transfer enzyme using NAD+.
• Tetrameric molecule with H and M subunits.
• Highest serum levels seen in pernicious anemia and hemolytic disorders.
• Elevated in AMI within 12-24 hours, peaking at 48-72 hours, elevated for 10-14 days.
• Hepatic carcinoma and toxic hepatitis show significantly elevated values.
• Elevated in viral hepatitis and cirrhosis.
• LD-5 is increased in acute viral hepatitis, cirrhosis, and hepatic carcinoma.
• LD-1 > LD-2 ("flipped pattern") in myocardial infarction and hemolytic anemia.

Creatine Kinase (CK)

• Dimeric molecule with M and B monomers.
• Primarily found in muscles and brain (CK-BB is predominant brain isoenzyme).
• CK-MB is significantly elevated in myocardial tissues.

5'-Nucleotidase (5'N)

• Phosphoric monoester hydrolase, primarily secreted from the liver.
• Marker for hepatobiliary disease and liver infiltrative lesions.

Gamma-glutamyl transferase (GGT)

• Useful in differentiating the cause of an increased ALP level.
• Elevated in hepatobiliary disorders and biliary tract obstructions,.

Pseudocholinesterase (PChE)

• Liver-secreted enzyme reflecting synthetic function rather than hepatocyte injury.
• Removes the benzyl group from cocaine.
• Marker for insecticide/pesticide poisoning (organophosphate poisoning); low PChE levels are seen.
• Useful to monitor the impact of muscle relaxants (such as succinylcholine) after surgery.