Evaluation of Uniformity and Stability of Frozen Mixed Serum Potassium Candidate Reference Materials

We tested the uniformity and stability of candidate reference materials (RMs) for serum potassium and aimed to design RMs with better quality that can meet all clinical test requirements and effectively solve the quantity traceability transfer problem.

Three levels of frozen mixed serum potassium candidate RMs were prepared and packed in freezing tubes. RMs were determined in triplicate in 10 vials randomly selected from each level. A one-way analysis of variance was used to evaluate the uniformity using a ratio of the mean squares among groups to mean squares within groups F < F0.05 as the criteria. Stability was studied by synchronization; the short-term stability of the serum potassium in the transport conditions was observed for 30, 15, and 7 days at refrigeration (2 - 8°C), room temperature (18 - 25°C), and 37°C, respectively. By linear regression analysis of variance, the straight line was used as an empirical model. The criterion for judging is |b1| < t0.95, n - 2·sb1.

Based on the statistical analysis using SPSS 17, the F values for the homogeneity tests of each level of the frozen mixed serum potassium RMs were 0.247, 0.117, and 0.162. These values were less than F0.05 (9, 20) = 2.39. When the short-term stability of the serum potassium was observed for 30, 12, and 4 days at 2 - 8°C, room temperature, and 37°C, respectively, |b1| < t0.95, n - 2·sb1, and instability was not observed.

The three levels of the frozen mixed serum potassium RMs have good uniformity. At 2 - 8°C, room temperature, and 37°C, the stability can be ensured for at least 30, 12, and 4 days, respectively. The serum potassium candidate RMs are sufficiently stable under these transportation conditions.