Optimized assay for serum angiotensin-converting enzyme activity.

Area of Science:

• Clinical Chemistry
• Enzyme Assays
• Biochemical Diagnostics

Background:

• Serum angiotensin-converting enzyme (ACE) levels are crucial biomarkers in various physiological and pathological conditions.
• Existing assays may be subject to interferences or lack optimal precision.
• A need exists for a robust and reliable method for quantifying serum ACE activity.

Purpose of the Study:

• To develop and validate an optimized two-point kinetic assay for serum angiotensin-converting enzyme (ACE).
• To establish the performance characteristics and reference intervals for the new assay.

Main Methods:

• The assay utilizes a colorimetric determination of hippurate released from hippuryl-L-histidyl-L-leucine.
• Angiotensin-converting enzyme (ACE) activity is measured in the presence of chloride ions.
• Assay validation included assessment of precision, linearity, and interference from common substances like lipemia, icterus, and hemoglobin.

Main Results:

• The optimized assay demonstrated excellent precision, with within-run and between-run coefficients of variation (CVs) ranging from 2.1% to 3.2%.
• Linearity was confirmed up to 200 U/L, indicating a wide dynamic range.
• The method showed minimal interference from lipemia and icterus, though high hemoglobin concentrations (>1.5 g/L) caused slight negative interference.
• Reference intervals were established as 22-82 U/L for men and 25-69 U/L for women.

Conclusions:

• The developed two-point kinetic assay provides a precise and reliable method for quantifying serum angiotensin-converting enzyme (ACE) activity.
• The assay's robustness against common interfering substances enhances its clinical utility.
• Established reference intervals aid in the accurate interpretation of serum ACE levels in patient populations.