Correction for effect of cold storage on immature platelet fraction.

It is common practice to store samples and measure the immature platelet fraction (IPF) only when the initial standard complete blood count and the blood smear indicate thrombocytopenia. However, the cold storage introduces an inherent error in the %IPF. A falsely elevated %IPF carries the risk of potentially misleading the clinicians' interpretation of the thrombopoietic activity, thus hindering the clinical utility of this parameter. To address this issue, we determined the IPF% in individual blood samples from 29 adults at 0, 4, 8, 10, 12, 21, and 24  hr after the blood draw. This study demonstrated that the effect of 4°C storage is linear over a 24  hr period and independent of the initial IPF%. These observations have enabled the development of a proposed algorithm for a corrected IPF%, which is equal to the uncorrected IPF% minus 1.34 times the length of time in hours of storage at 4°C. The proposed correction algorithm extends the utility of this clinically important laboratory parameter. However, care should be taken not to extrapolate the algorithm significantly beyond 24  hr storage, because the experimental data only covered this range.