Standard -20 °C freezer storage protocols may cause substantial plasma renin cryoactivation

Area of Science:

• Clinical Chemistry
• Biochemistry
• Analytical Chemistry

Background:

• Accurate renin concentration analysis is crucial for diagnosing and managing various endocrine and cardiovascular conditions.
• Variations in preanalytical sample handling, particularly long-term storage, can significantly impact renin assay results.
• Observed inconsistencies in renin measurements within a network highlighted the need to optimize preanalytical processes.

Purpose of the Study:

• To evaluate the impact of different freezing and storage conditions on plasma renin concentration.
• To identify the optimal preanalytical method for preserving renin activity during sample storage.
• To investigate the phenomenon of cryoactivation in plasma samples intended for renin analysis.

Main Methods:

• Pooled plasma samples were analyzed for renin concentration immediately after separation.
• Aliquots were subjected to various storage conditions: -20°C freezer, snap freezing (dry ice/acetone), room temperature, and 4°C.
• Renin concentrations were compared to baseline, with subsequent experiments exploring cryoactivation sources.

Main Results:

• Freezing plasma at -20°C induced substantial and variable cryoactivation, increasing renin concentration by over 300% in some samples.
• Snap freezing effectively prevented cryoactivation.
• Initial rapid freezing at -70°C followed by storage at -20°C also prevented cryoactivation, and rapid thawing was not necessary.

Conclusions:

• Standard -20°C freezers are inappropriate for plasma storage for renin analysis due to cryoactivation.
• Laboratories should adopt snap freezing using a -70°C freezer or equivalent method to prevent renin cryoactivation.
• Optimized preanalytical procedures are essential for reliable renin concentration measurements.