Liver diseases are commonly diagnosed using serum enzyme assays, particularly for aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), gamma-glutamyl transpeptidase (GGT), and 5'-nucleotidase (5'-NT). While elevated levels of these enzymes are typically associated with liver and bile duct injuries, subnormal levels can also indicate various pathologies. This review consolidates current knowledge on diseases linked with subnormal liver enzyme levels, focusing on their pathogenesis, specificity, and treatment implications.
Aminotransferases: ALT and AST, critical for amino acid metabolism, are mainly found in hepatocytes but also exist in renal, cardiac, and skeletal tissues. ALT is more specific to the liver, while AST is present in both cytoplasm and mitochondria. Subnormal aminotransferase levels can result from deficiencies in pyridoxal 5'-phosphate (PLP, vitamin B6), often seen in conditions such as: Alkaline Phosphatase (ALP): ALP, a membrane-bound glycoprotein involved in phosphate metabolism, has several isozymes (intestinal, placental, germ-cell, tissue-nonspecific).
Subnormal ALP levels are associated with: Gamma Glutamyl Transferase (GGT): GGT is important in glutathione metabolism and is a marker for bile duct function. Subnormal levels are noted in: 5'-Nucleotidase (5'-NT): This enzyme is involved in nucleotide metabolism. Low levels can indicate: Subnormal serum levels of liver enzymes are clinically significant and can ind.