Enzyme analysis is used to aid in diagnosis and treatment of disease. In particular, enzymes that are synthesized within cellular organelles carry out their functions within cells and are released into body fluids when those cells become diseased.

Thus, an increase in enzyme activity when compared to the reference range can indicate pathological changes in certain types of cells and tissues. Enzyme activity levels in body fluids can reflect leakage from cells due to cellular injury, or changes in enzyme production rate or actual enzyme induction due to metabolic or genetic states or proliferation of neoplasms.

Damage to tissue can release different types of enzymes based on their location. For example, mild inflammation of the liver reversibly increases the permeability of the cell membrane and releases cytoplasmic enzymes such as lactate dehydrogenase (LD), alkaline phosphatase (ALP), Alanine Transaminase (ALT), and Asparte Transaminase (AST), while cellular death (necrosis) will release mitochrondrial sources of ALT and AST.

Distribution of these enzymes within specific types of hepatic tissues varies. ALP and γGT are more concentrated in the biliary ducts or tissues of the small ducts (canaliculi), while AST, ALT, and LD are found mainly in structural (parenchymal) hepatic cells.

Multiple forms of enyzmes, called isoenzymes, are distributed in several different tissue types. For example, ALP is found in hepatobiliary tissues but also found in all cytoplasmic membranes of all cells of the body, especially in osteoblasts (bone forming cells), intestinal mucosa, placenta, and renal tubules.

Correlation of patterns of hyperbilirubinemia with serum enzymes may also be helpful. For example, prehepatic jaundice, as indicated by relatively normal serum conjugated bilirubin, increased unconjugated bilirubin, and increased urinary urobilinogen, correlates with normal serum levels of hepatocellular and hepatobiliary enzymes, with the exception of LDH and possibly AST. These two enzymes are found in erythrocytes so, in situations of increased red blood cell breakdown, these enzyme concentrations are elevated in the serum.

Hepatic jaundice, indicated by increased serum conjugated and unconjugated bilirubin and increased urinary urobilinogen, correlates with increased serum levels of hepatocellular enzymes. Posthepatic jaundice, as indicated by relatively normal serum unconjugated bilirubin, increased conjugated bilirubin, and decreased urinary urobilinogen, correlates with pronounced elevations of hepatobiliary enzymes but normal to slightly elevated serum levels of hepatocellular enzymes.


INTERPRETATION OF ALKALINE PHOSPHATASE RESULTS

Dr. Essam (Eldin Mohammed Nour Eldin ,Professor of Medical Biochemistry, Faculty of Medicine, Umm Al-Qura University)

ALP is found in high concentration in hepatobiliary cells. Inflammation or obstruction of the biliary ducts may cause disruption of these cells, which causes the release of ALP into the circulation. Serum ALP levels of patients who have cholestasis may be increased 3 to 10 times the normal levels.

ALP is present in the cells of most tissues in the body, including the liver, bone, intestinal epithelium, kidney tubules, and placenta. Several isoenzymes of the catalysts are associated with specific tissues and can be used to identify pathological processes in these tissues.

Serum ALP levels may also be increased when there is a high amount of osteoblastic activity (cells rebuilding bone). ALP levels of 10 to 25 times normal may be seen in such patients. Most of the ALP that is found in the circulation has its origin in liver or bone tissue cells.

LIVER ENZYMES NORMAL VALUES
SGPT-Serum Glutamate Pyruvate Transaminase or ALT- Alanine Transaminase 6.0-59 u/L
SGOT-Serum Glutamic Oxaloacetic Transaminase or AST- Aspartate Transaminase 10-34 u/L
ALP- Alkaline Phosphatase 20-140 IU/L
Bilirubin direct BIL 0-0.3 mg/dL
                  total BIL 0.3-1.9 mg/dL
Cholesterol 140-310 mg/dL
       optimal 140-220 mg/dL
Total protein 6.4-8.3 g/dL
Alpha-1 Globulin 0.1-0.3 g/dL
Alpha-2 Globulin 0.6-1.0 g/dL
Beta Globulin 0.7-1.2 g/dL
Gamma Globulin 0.7-1.6 g/dL
Triglycerides 10-190 mg/dL
High Density Lipoprotein (HDL) 30-100 mg/dL
Low Density Lipoprotein (LDL) 60-120 mg/dL
Total Cholesterol 100-240 mg/dL
Lactate Dehydrogenase (LDH) 105-333 IU/L