Predicting a donor's likelihood of donating within a preselected time interval

The procurement of some advanced blood components, like quarantined plasma units, depends critically on retesting the donor within a fixed time frame. For health care systems, such as that in Germany, with mandatory retesting of donors before plasma release, the reliable identification of donors who are more likely to return in time has an immense practical implication, because their blood components could be preferably selected for quarantine purposes. The donation histories of about 760 000 donors with 4910 000 donation attempts were analysed. We developed a logistic regression model to calculate a probability of donation, p(Dts-te), within a preselected time frame (ts-te). The donation history was compounded in a score and shown to be very useful for determining p(Dts-te). A logistic regression model was developed with score and donor status as parameters; different regression coefficients applied to first-time-donors (ftd) and to repeat donors (intercept, int, and score factor, scf ). This model allowed us to determine the probability of donation, p(Dts-te), within a preselected time interval, e.g. 6-9 months after an index donation. The p(Dts-te) can be calculated for any donor of blood services. The p(D170-275 days) ranged from about 22% to 86% for any index donation in 1996/97. First-time donors had a p(D170-275 days) of 33% and were more likely to return within the time interval than certain subsets of repeat donors who can be defined by our model. We provided a technical procedure to increase the rate of plasma unit release after quarantine storage and showed the usefulness of our procedure for blood component management, if quarantine storage is required. By applying the model to our current plasma quarantine programme we could retrieve about 30% more units, which would represent about 30 000 units per year, without incurring additional costs. General implications for blood collection, like planning blood drives, were discussed. The whole demand of a health care system for single plasma units may be met by quarantine plasma and their cost-efficiency can be improved.