Clinical Chem - Enzymes

Creatine Kinase (CK)

Source

Skeletal muscle, Heart, Brain

Purpose

Regeneration and storage of ATP

Diagnostic Significance

CK-MB → MI

CK-MM → Muscular dystrophy

CK-BB → CNS disorders

Sources of Error

Hemolysis

Exposure to light

References Ranges

Men have higher CK

Assay

Isoenzyme electrophoresis

Lactate Dehydrogenase (LDH/LD)

Source

Everywhere

Purpose

Catalyzes a reversible reaction between pyruvate and lactate with NAD as a coenzyme

Diagnostic Significance

LD1 > LD2 (LD Flip) → MI

Elevated LD5 → Muscle or Liver disease

Central Fractions Elevated → Lung sources or malignancy, not diagnostic

All Fractions Elevated → Shock, Sepsis

Sources of Error

Hemolysis

Analyte stability → ASAP or store at room temp

Prolonged contact of serum/cells

References Ranges

125-220 U/L

Assay

NADH system

Aspartate transaminase (AST)

Source

Liver

Purpose

Synthesis and degradation of amino acids

Diagnostic Significance

Cirrhosis, Hepatitis, Liver cancer

MI

Sources of Error

Hemolysis

Stable at room temp for 48 hours

References Ranges

5-35 U/L

Assay

NADH system at 340nm

Alanine Transaminase (ALT)

Source

Liver

Purpose

Transfers an amino group from alanine to alpha-ketoglutarate to form glutamate and pyruvate

Diagnostic Significance

Cirrhosis, Hepatitis, Liver cancer

Sources of Error

Unaffected by hemolysis

References Ranges

Assay