How long can samples be stored at -20 C?

• A. 1 day
• B. 1 week
• C. 2 weeks
• D. 1 month

Answer: (C)

Freezing slows biochemical processes, but -20 C isn’t as protective as ultra-low temperatures, so the storage window is limited for most routine samples. For many serum or plasma specimens used in routine clinical chemistry, keeping them frozen at -20 C without significant degradation is typically about two weeks, provided they avoid repeated freeze-thaw cycles. If you need longer storage, moving to -80 C (or even colder) and aliquoting to reduce freeze-thaw is advised.

One day is too short to take full advantage of freezing. One week can work for some very stable samples, but two weeks is the commonly accepted safe window for many routine specimens at -20 C. One month is generally too long at this temperature for preserving most analytes without changes.