Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1040 page)

   Hepatitis—most marked increase is of LD-5, which occurs during prodromal stage and is greatest at time of onset of jaundice; total LD is also increased in 50% of the cases. LD increase is isomorphic in infectious mononucleosis. An ALT-to-LD or AST-to-LD ratio within 24 hours of admission ≥1.5 favors acute hepatitis over acetaminophen or ischemic injury.

   Acute and subacute hepatic necrosis: LD-5 is also increased with other causes of liver damage (e.g., chlorpromazine hepatitis, carbon tetrachloride poisoning, exacerbation of cirrhosis, or biliary obstruction) even when total LD is normal.

   Metastatic carcinoma to the liver may show marked increases. It has been reported that an LD-4–to–LD-5 ratio <1.05 favors diagnosis of hepatocellular carcinoma, compared to a ratio >1.05, which favors liver metastases in >90% of cases.

   If liver disease is suspected but total LD is very high and isoenzyme pattern is isomorphic, rule out cancer.

   Liver disease, per se, does not produce marked increase of total LD or LD-5.

   Various inborn metabolic disorders affecting the liver (e.g., hemochromatosis, Dubin-Johnson syndrome, hepatolenticular degeneration, Gaucher disease, McArdle disease).

   
Hematologic diseases

   Untreated PA and folic acid deficiency show some of the greatest increases, chiefly in LD-1, which is >LD-2 (“flipped”), especially with Hb <8 g/dL.

   Increased in all hemolytic anemias, which can probably be ruled out if LD-1 and LD-2 are not increased in an anemic patient; normal in aplastic anemia and iron deficiency anemia, even when the anemia is very severe.

   
Diseases of the lung

   Pulmonary embolus and infarction—pattern of moderately increased LD with increased LD-3 and normal AST 24–48 hours after onset of chest pain

   
Normal value:
<1.3 pmol/L.