What is the normal percentage range for the LD5 isoenzyme in serum?

What is the normal percentage range for the LD5 isoenzyme in serum?

• A. 6-16%
• B. 29-39%
• C. 14-26%
• D. 20-26%

Answer: (A)

LDH has five different isoenzymes, and in healthy serum the pattern is led by LDH-1 and LDH-2 with smaller amounts of the others. LDH-5, the liver and skeletal muscle isoenzyme, is normally present only in a small fraction of total LDH. That’s why the typical normal range for LDH-5 is about 6–16%. When liver or muscle tissue is damaged, LDH-5 can rise, shifting the overall LDH pattern toward a higher LDH-5 percentage. The other ranges would suggest a higher baseline LDH-5 than expected in a normal serum.

LDH has five different isoenzymes, and in healthy serum the pattern is led by LDH-1 and LDH-2 with smaller amounts of the others. LDH-5, the liver and skeletal muscle isoenzyme, is normally present only in a small fraction of total LDH. That’s why the typical normal range for LDH-5 is about 6–16%. When liver or muscle tissue is damaged, LDH-5 can rise, shifting the overall LDH pattern toward a higher LDH-5 percentage. The other ranges would suggest a higher baseline LDH-5 than expected in a normal serum.