Given a rate reaction for alanine aminotransferase, which value would represent the activity of a serum specimen in international units per liter (IU/L)?

Given a rate reaction for alanine aminotransferase, which value would represent the activity of a serum specimen in international units per liter (IU/L)?

• A. 186
• B. 198
• C. 1857
• D. 1869

Answer: (D)

Enzyme activity in IU/L is defined as the amount of enzyme that catalyzes the formation of 1 μmol of product per minute under the assay conditions. For ALT, the assay measures how fast pyruvate is produced, in μmol per minute per liter. Because 1 IU corresponds to 1 μmol per minute, the numerical value of the rate in μmol/min/L directly equals the activity in IU/L. So if the measured rate is 1869 μmol/min/L, the activity is 1869 IU/L. Therefore the value that represents the activity is 1869 IU/L.

Enzyme activity in IU/L is defined as the amount of enzyme that catalyzes the formation of 1 μmol of product per minute under the assay conditions. For ALT, the assay measures how fast pyruvate is produced, in μmol per minute per liter. Because 1 IU corresponds to 1 μmol per minute, the numerical value of the rate in μmol/min/L directly equals the activity in IU/L. So if the measured rate is 1869 μmol/min/L, the activity is 1869 IU/L. Therefore the value that represents the activity is 1869 IU/L.