Which clinical disorder is associated with the greatest elevation of lactate dehydrogenase (LD) isoenzymes?

• A. Pneumonia
• B. Glomerulonephritis
• C. Pancreatitis
• D. Pernicious anemia

Answer: (D)

LD isoenzymes vary by tissue, and red blood cells contribute a lot of the LD-1 form. When there’s destruction of erythroid cells, especially in conditions with intramedullary (inside the bone marrow) hemolysis like pernicious anemia, a large amount of LD is released into the blood, with LD-1 (the form most abundant in RBCs) rising prominently. That pattern leads to a marked overall LD elevation.

In contrast, the other disorders mostly affect different tissues and tend to shift toward other LD isoenzymes (lung tissue for LD-3, liver/skeletal muscle for LD-5, etc.) and don’t produce as striking an increase driven by red cell LD. That’s why pernicious anemia is associated with the greatest elevation of LD isoenzymes.