Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1042 page)

   Hypothyroidism, subacute thyroiditis

   Collagen vascular diseases

   Acute pancreatitis

   Intestinal obstruction

   Sarcoidosis

   Various CNS conditions (e.g., bacterial meningitis, cerebral hemorrhage, or thrombosis)

   Drugs

Decreased In

   Irradiation

   Genetic deficiency of subunits

   Limitations

   RBCs contain much more LD than serum. A hemolyzed specimen is not acceptable.

   LD activity is one of the most sensitive indicators of in vitro hemolysis. Causes can include transportation via pneumatic tube, vigorous mixing, or traumatic venipuncture.

LACTATE DEHYDROGENASE ISOENZYMES

   Definition

   LD is a tetrameric cytoplasmic enzyme. The most usual designation of the isoenzyme is LD-1 (H[4]), LD-2 (H[3]M), LD-3 (H[2]M[2]), LD-4 (HM[3]), and LD-5 (M[4]). The tissue specificity is derived from the fact that there is tissue-specific synthesis of subunits in well-defined ratios. Most notably, heart muscle cells preferentially synthesize H subunits, whereas liver cells synthesize M subunits nearly exclusively. Skeletal muscle also synthesizes largely M subunits so that LD(5) is both a liver and skeletal muscle form of LD. The LD-1 and LD-5 forms are ones most often used to indicate heart or liver pathology, respectively. LD isoenzyme patterns cannot be interpreted without the knowledge of clinical history (see Table 16.52).