Storage stability of commonly used haematological parameters at 33 °C: Electronic supplementary material available online for this article.

INTRODUCTION: This study aimed to investigate the analytical bias in haematological parameters induced by storage at 33 ºC. MATERIALS AND METHODS: Blood from the diversion pouch of 20 blood donors were collected in K((2))EDTA vials and stored at 33 ºC. Readings from each vial were taken at 0, 4, 6, 12, 24, 48 and 72 hours after collection on the Sysmex XP-100 analyser (Sysmex Corporation, Kobe, Japan). The percent difference from the baseline readings were calculated and subjected to a Wilcoxon signed rank test at a Holm corrected significance level of 0.05. A median percent difference, which was statistically significant and greater than the maximum acceptable bias (taken from studies of biological variation), was taken as evidence of unacceptable shift. If the median shift was lesser than the maximum acceptable bias, two one-sided Wilcoxon signed rank tests for equivalence were used to determine whether the percent differences were significantly lesser than the maximum acceptable bias. RESULTS: Haemoglobin, red blood cell count, white blood cell count, mean corpuscular haemoglobin and lymphocyte count showed acceptable bias after storage for at least 24 hours at 33 ºC. Haematocrit, mean corpuscular volume, mean corpuscular haemoglobin concentration, platelet count and mean platelet volume showed unacceptable shift in less than 4 hours when stored at 33 ºC. CONCLUSIONS: Since many haematological parameters show unacceptable bias within 4 hours of sample storage at 33 ºC, the recommended limit of time from collection to processing should be revised for areas where high environmental temperatures are common.