Methodologic issues in the measurement of urinary renin

Area of Science:

• Biochemistry
• Renal Physiology
• Assay Development

Background:

• Urinary renin is a potential prognostic biomarker for acute kidney injury (AKI).
• Previous studies reported unusually high urinary renin levels, questioning assay specificity.
• A new Quantikine Renin ELISA Kit was investigated for its accuracy in measuring total renin.

Purpose of the Study:

• To evaluate the accuracy and specificity of a new Quantikine Renin ELISA Kit.
• To compare ELISA measurements with established renin assays.
• To investigate the discrepancy in reported urinary renin levels.

Main Methods:

• Compared ELISA with immunoradiometric and enzyme kinetic assays using plasma and urine from patients and healthy individuals.
• Measured renin and prorenin levels before and after in vitro prorenin activation.
• Assessed assay performance against the International Reference Preparation of human renin.

Main Results:

• ELISA measurements for total renin were consistently ≥10-fold higher than other assays.
• The ELISA kit's standard was identified as prorenin, with lower activity than the reference standard.
• Urine samples showed no detectable prorenin, while plasma had 10%-15% prorenin.

Conclusions:

• The Quantikine Renin ELISA Kit overestimates urinary and plasma renin levels due to its prorenin standard.
• Assay inconsistencies necessitate the use of established renin assays for accurate measurements.
• Accurate urinary renin measurement is crucial for its role as a prognostic biomarker.