Reply to: Letter to the Editor From A.H. Jan Danser and Ingrid M. Garrelds: The Clinical Impact of Sample Storage at −20 °C on Renin Reference Intervals and Aldosterone-renin Ratio Calculations.

This article is a response to a letter from A.H. Jan Danser and Ingrid M. Garrelds regarding the clinical impact of sample storage at -20 °C on renin reference intervals and aldosterone-renin ratio calculations. The authors of the response paper argue that cryoactivation of prorenin is a preanalytical risk for renin measurements in plasma samples stored at -20 °C. They cite experiments that show highly variable increases in renin concentration when samples are frozen at -20 °C, but no cryoactivation when samples are snap-frozen or defrosted at ambient temperature. Based on this evidence, the authors advise laboratories to store plasma samples for renin analyses in a -70 °C freezer or snap-freeze samples and store them in a -20 °C freezer. [Extracted from the article]