Digital droplet polymerase chain reaction to monitor ultraviolet C treatment of single‐donor and buffy coat platelet units

BACKGROUND UVC illumination of agitated platelet concentrates (PCs) inactivates pathogens and white blood cells by modifications of their nucleic acids. Related effects on mitochondrial DNA (mtDNA) in platelets serve as a basis for an efficient monitoring suited for routine quality control (QC) of this purely physical pathogen reduction technology. STUDY DESIGN AND METHODS Samples from PCs (n = 530) were tested with an established LightCycler PCR (LC PCR) for QC of the UVC procedure. RNR2 and TRNK/ATP8 genes were sequenced in the PCs (n = 21) with out‐of‐specification results in the LC PCR. A digital droplet PCR (ddPCR) was developed to minimize the outliers and cross‐validated by testing the 530 PCs. The ddPCR was further evaluated in a subgroup of 300 PCs without mtDNA extraction and in samples from systematic variations of UVC dose and agitation speed. RESULTS Apheresis PCs (n = 380) resulted in 5.3% outliers in LC PCR versus only 0.7% in buffy coat pool PCs (n = 150). Sequencing of these outliers revealed single‐nucleotide polymorphisms in the primer‐ and probe‐binding sites of LC PCR. The development of a ddPCR assay with modified probe sequences reduced the outliers to 0.4%. The ddPCR analysis of PCs both with and without mtDNA extraction demonstrated low intra‐ and interassay variabilities and congruent results also compared to LC PCR. Experiments varying the UVC dose and the agitation speed demonstrated that the ddPCR results closely reflect functional effects of the UVC treatment. CONCLUSION The ddPCR assay offers a valid and reliable tool for QC of routine production of the UVC‐treated PCs as well as for monitoring treatment conditions during optimization of the UVC procedure.