Refrigerated storage stability of 11 humoral parameters in two different venous blood collection tubes over a 7-day period.

OBJECTIVES: Humoral parameters like immunoglobulins, complement components, and free light chains (FLC) are vital for diagnosing immune and hematological disorders. To minimize pre-analytical errors and reduce turnaround time, this study evaluated the 7-day stability of 11 analytes (IgG, IgG subclasses 2-4, IgA, IgM, C1 esterase inhibitor, C3c, C4, and FLC Kappa/Lambda) to determine if manual aliquoting can be eliminated in favor of direct primary tube sampling. METHODS: Blood from 27 healthy volunteers was collected into lithium heparin (LH) and LH-gel separator (LH-GS) tubes. Baseline measurements (Day 1) from aliquoted samples were compared against samples stored at 2-8 °C and re-tested on Days 3 and 7 using the Optilite® analyzer. Stability was defined by the percent difference (%PD) against total error (TEa) limits. RESULTS: IgG (and subclasses), IgA, IgM, and C4 remained highly stable through Day 7 in both tube types. FLCs (Kappa/Lambda) showed a progressive negative bias but stayed within acceptable limits. Conversely, C3c exhibited significant positive bias, exceeding stability limits by Day 7 (%PD 10.39 in LH); it was only stable up to Day 3. No interference from the gel separator was detected. CONCLUSIONS: Aliquoting can be safely omitted for most humoral parameters, allowing for direct primary tube sampling and streamlined workflows. While FLCs remain reliable for 7 days, C3c requires a strict 3-day window. Both LH and LH-GS tubes are suitable, supporting laboratory optimization and ISO 15189 compliance while maintaining analytical quality.