Resolving variable maternal D typing using serology and genotyping in selected prenatal patients.

BACKGROUND: RhIG prophylaxis for D- pregnant women prevents hemolytic disease of the newborn and typically depends on results of serologic D typing. Interpretation and follow-up of weak D serology is variable. Recent recommendations promote genotyping for RHD status determination in those with weak D serology. Canadian Blood Services performs comprehensive serologic prenatal testing in four provinces. Genotyping is used to determine D typing in patients with weak D. STUDY DESIGN AND METHODS: A serologic algorithm identified which patients require genotyping for RHD determination. Genotyping was performed on one of two commercially available platforms. RESULTS: Only 0.4% of D- patients met criteria for genotyping. Sixty-one percent were weak D Type 1, 2, or 3. Thirty percent had a partial or weak D other than Type 1, 2, or 3. Eleven had variants which remained unresolved. Seventeen were D+ and four were D-. CONCLUSIONS: Genotyping of patients with weak D serology led to an identified genotype in most patients. RhIG administration was avoided in 66% who were weak D Type 1, 2, or 3 or were D+. The use of a serologic algorithm to select patients for RHD genotyping identifies a majority of patients with weak D types not at risk for alloimmunization. This approach limits the number of genotyping investigations and the cost of providing classification for weak D types.

Intermittent bacteremia detected in an asymptomatic apheresis platelet donor with repeat positive culture for Escherichia coli: a case report.

BACKGROUND: Bacterial culture of platelet concentrates (PCs) has been implemented to reduce the risk of infectious transfusion events. Most positive cultures are for skin flora or environmental organisms with no underlying pathology associated in the donor. Less frequently, enteric organisms have been isolated from PCs indicating asymptomatic donor bacteremia. We report a case of a donor with repeat positive culture for Escherichia coli. CASE REPORT: A 62-year-old single apheresis platelet (PLT) donor who passed all routine screening procedures had two intermittent positive BacT/ALERT cultures with E. coli. On both occasions, transfusion was prevented with the contaminated units. The donor denied any symptoms suggestive of infection and was referred to his family physician for evaluation. A barium enema revealed multiple colonic diverticula, although the donor has remained asymptomatic. Based on his history of repeat-positive cultures with the same enteric organism, the donor has been permanently deferred. DISCUSSION: PLT screening for bacterial contamination has been an effective measure to reduce the incidence of septic transfusion reactions. Important is the capture of Gram-negative bacteria, which can be involved in septic shock due to the production of endotoxins. In addition to the safety benefit to PLT recipients, PLT culture is valuable for blood donors. The recurrence of positive cultures with the same organism allows the identification of subclinical illnesses and, if appropriate, deferral from blood donation. CONCLUSION: This asymptomatic donor has intermittent bacteremia likely related to diverticular disease. Isolation of E. coli twice prompted further investigation and donor deferral.

West Nile virus in Canadian blood donors.

BACKGROUND: Blood donation screening for West Nile virus (WNV) RNA by nucleic acid testing (NAT) was implemented in Canada in July 2003, and 14 WNV RNA-positive donations were identified. Samples were screened in minipools of six donations with a WNV assay (TaqScreen, Roche). Two of the donors were identified by single-donor screening that was initiated in the province of Saskatchewan, which had the highest prevalence of WNV in the country, in early September 2003. STUDY DESIGN AND METHODS: The original 14 samples and follow-up samples (2-35 days after donation), available from 13 of the 14 donors were tested with an in-house, real-time, quantitative WNV NAT assay that was specific for WNV. A Health Canada reference reagent was used for calibration. Immunoglobulin M (IgM) and immunoglobulin G (IgG) levels were determined with commercial enzyme-linked immunosorbent assay kits. RESULTS: All donors tested positive for the presence of WNV with the in-house assay. Two donors, 18 and 19, identified by single-donor testing, had extremely low levels of viremia and that could only be detected in 1:38 or 1:39 replicate tests. The titers of the remaining index samples ranged from below log2.8 (the limit of quantitation) to log4.7 NAT detectable units per mL. Three samples, from Donors 17, 18, and 19, were IgM-positive, whereas samples from Donors 18 and 19 were also IgG-positive. The remaining 10 donors with follow-up samples all seroconverted. CONCLUSION: The 14 WNV donor samples detected by routine screening were confirmed as WNV RNA-positive by a WNV RNA-specific in-house assay and by demonstration of seroconversion in 13 of the 14 donors.