143-P: ACCURACY OF HLA TYPING ON CORD BLOOD UNITS: SAMPLE SWITCHES ARE AN INCREASING EVENT

Aim The NMDP facilitates extended and verification HLA typing (ET/VT) of cord blood units (CBUs) from the Be The Match ® Registry. A retrospective review of HLA discrepancies was performed to determine overall error rates and causes. Methods Initial HLA testing of CBUs for listing on the registry was performed by a variety of typing methods including serology and DNA based methods while ET/VT was performed with DNA based methods. An HLA typing discrepancy was captured when the ET/VT typing was not concordant with registry typing. Results The number of CBU ET/VTs has increased by 2.5 times from 2007 to 2011 while the rate of HLA discrepancies has fallen from 3.9% in 2007 to 1.2% in 2011, which is similar to the worldwide rate of 1.1% reported by the WMDA in 2011. Usage of filter paper spotted from a contiguous segment for ET/VT has increased over this time period, and comprises more than half of all sample types in 2011 (data not shown). Among the technical errors causing discrepancies, 6% were at ET/VT and 94% were from recruitment typing. Interestingly, sample switches seem to be increasing as a proportion of the causes of discrepant typing. There were no sample switches at the ET/VT labs. Conclusions With the numbers of the CBU ET/VTs more than doubling, the discrepancy frequency shows a strong decreasing trend over the last 5 years. Technical errors at recruitment continue to constitute the major causes of HLA discrepancies identified at ET/VT, but sample switches show an increasing trend and should be monitored closely [ Table 1 ].