How long can refrigerated serum samples be stored before analysis?

• A. 8 hours
• B. 24 hours
• C. 72 hours
• D. 1 week

Answer: (B)

When a serum sample is kept in the refrigerator, the goal is to slow down any ongoing chemical or enzymatic changes that could alter the measured results. For most routine serum chemistry tests, a practical and commonly accepted window is about 24 hours at 2–8°C. Within this period, the risk of significant drift in analyte concentrations is minimized, making the results reliable for analysis.

If storage extends beyond 24 hours, some analytes can start to drift—for example, glucose can decrease due to residual glycolysis, and other components may degrade or change slightly. Because of these potential changes, longer refrigerated storage is not considered safe for general use. For longer storage, freezing is used (typically at -20°C or -80°C), but this comes with its own caveats, such as potential effects from freeze–thaw cycles on certain tests.

The other time frames are less appropriate: 8 hours is often insufficient for typical workflow delays, while 72 hours or a week increases the risk of substantial analytic bias and is not recommended for routine refrigerated storage.