[Measurement of angiotensin-I-converting enzyme in the blood: help for method validation]

Area of Science:

• Clinical Biochemistry
• Enzymology

Background:

• Blood angiotensin-converting enzyme (ACE) activity is typically measured using synthetic substrates like FAPGG.
• Current assays are optimized for serum or plasma and may not be suitable for other biological fluids like cerebrospinal fluid due to lower ACE activity.

Purpose of the Study:

• To describe the adaptation and validation of a blood ACE assay for automated biochemistry analyzers.
• To outline sample handling, storage, and assay performance characteristics.

Main Methods:

• Enzyme activity determination using the synthetic substrate furylacryloyl-phenylalanyl-L-glycyl-L-glycine (FAPGG).
• Adaptation of the assay to various automated biochemistry analyzers.
• Evaluation of sample stability and storage conditions (+4°C for one week, -20°C without refreezing).

Main Results:

• The assay demonstrates linearity from 10 to 200 UI/L with excellent fidelity after calibration.
• Analytical uncertainty ranges from 2% to 5%, depending on serum ACE levels.
• ACE activity may be higher in adolescent males, with further studies on age and sex expected.

Conclusions:

• The described blood ACE assay is robust, accurate, and adaptable to automated platforms for clinical use.
• Understanding ACE activity variations is crucial for diagnosing conditions like sarcoidosis and monitoring ACE inhibitor therapy.