A historical perspective on platelet radiolabeling techniques

Procedures to evaluate platelet (PLT) recovery and survival have continued to evolve through the years. In the early 1960s, PLT labeling with 51 Cr required a large volume of PLTs and labeling in a bag with low efficiency. In 1977, the ICSH recommended standardization of PLT survival determination with 51 Cr and labeling the PLT‐rich plasma in a bag; however, issues of poor 51 Cr uptake and label manipulation in a large bag still existed. In the mid 1970s, a new radiolabel with 111 In was established. Similar recovery and survival results to 51 Cr were reported, with the benefits of less blood required and the ability to perform external imaging. A symposium in 1984 detailed recommendations of protocols for radiolabeling of stored PLT concentrates with either 111 In or 51 Cr and for statistical analysis. Although label preparations did not become standardized, agreement was reached that the best method to determine survival was the gamma nonlinear multiple‐hit model. In 1992, Heaton and Holme showed that concurrent double PLT labels showed a much higher correlation than those separated chronologically and that radiolabel corrections for elution and cell contamination and similar 111 In and 51 Cr labeling procedures were necessary. The 2004 NIH symposium proposed standardization of the PLT‐labeling method with a control of fresh PLTs compared to the stored PLT product, both from the same donor and with the double‐label 111 In‐ 51 Cr method. The procedure included in this supplement represents the evolutionary distillation of numerous approaches and provides a well‐researched, standardized, and dependable means of radiolabeling PLTs.