The donor line break cannula: effect on the donation process, blood component quality and transfusion microbiology testing of an important new blood bag safety feature.

BACKGROUND: The use of blood packs with an integral sampling system can result in anti-coagulant from the main bag reaching the sample pouch via the donor line, causing delayed coagulation of blood samples. In NHS Blood and Transplant, this has prevented the use of serum, the preferred matrix for transfusion microbiology (TM) testing, which has led to an increased false positive rate with ethylenediaminetetraacetic acid (EDTA) plasma. There is also a remote possibility of false negative results owing to sample dilution. Manufacturers have responded by offering packs with a donor line break cannula (DLBC) to prevent these adverse effects. OBJECTIVES: The aims of this study were to assess the impact of DLBC packs on donation, blood component quality and of the potential return to serum for TM testing. METHODS: DLBC packs from three manufacturers were assessed against control packs of the same dimensions and configuration. Donation duration, flow rate, platelet factor 4, prothrombin fragment 1+2, haemolysis and collection and processing incidents were compared. RESULTS: Results indicated no clinically significant adverse effect from the DLBC on the activation state of platelets, the coagulation cascade or increased haemolysis. Donation duration and blood collection and processing incident rates for DLBC packs were not significantly different to controls. CONCLUSIONS: The use of DLBC packs would reduce the complexity of manipulations during blood collection and therefore the likelihood of microbially contaminated donations (incorrect skin core diversion) and false negative TM tests. DLBC packs would enable the use of serum for TM testing with a significant reduction in false positive tests compared to EDTA plasma.

Improvement in the performance of HIV screening kits.

SUMMARY: The aim of this study was to assess the performance of HIV screening kits introduced over a 12-year period. HIV kits used by the National Blood Service (NBS) were assessed in the context of other HIV kits employed by diagnostic and reference laboratories. Thirty-three HIV screening kits were assessed and 13 had the potential to be used by the NBS. Specimens applied to NBS evaluations included 2000 HIV-negative specimens collected from blood donors, 200 HIV-positive specimens and 21 seroconversion panels, with larger numbers applied to the latter two categories prior to implementation of Communauté Européennes (CE) marking. The 33 HIV kits gave repeat reactive rates, based on HIV-negative specimens, of between 0% and 0.8% (and between 0% and 0.2% for kits relevant to the NBS). When examined for diagnostic sensitivity, the 33 kits gave sensitivities between 99.78% and 100%. Kits relevant to NBS gave sensitivities of 100% except one kit, which failed to detect one anti-HIV-2-positive specimen. Twenty-six kits were compared for detection of primary HIV infection. Of these, the 10 combined HIV antigen/antibody kits examined were more sensitive than other formats and have been exclusively adopted by NBS where operational considerations allow. Their added seroconversion sensitivity makes them the screening method of choice for populations at increased risk, e.g. in sexually transmitted infection (STI) clinics. The regular review of evaluation results has demonstrated a continuing improvement over time in the performance of HIV screening kits and contributed to advances in blood safety.

Enzyme linked immunosorbent assay (ELISA) for cytomegalovirus antibody in donor plasma.

An adaptation of an enzyme immunoassay technique was developed to screen donor plasma for high titres of antibodies to cytomegalovirus (CMV). The technique uses microtitre plates treated with glutaraldehyde and coated with CMV antigen and an anti-IgG alkaline phosphatase conjugate to detect the captured antibody. Using an anti-CMV standard with a 1/64 titre by complement fixation, 34 (6.8%) of 500 sera were shown to have an antibody titre that was acceptable to the Blood Products Laboratory in England for anti-CMV immunoglobulin production.

The systematic monitoring of transfusion microbiology test kit performance.

The Transfusion Microbiology Test Systems Monitoring Group (TMTSMG) was established as a National Blood Service (NBS) working group to monitor the performance of the microbiology screening assays used within the NBS Testing Laboratories. The group's primary objective was to ensure that technical performance (especially sensitivity, specificity and wastage) remains consistent with that established during validation. This includes the identification and investigation of significant variation in performance and any untoward incidents. The group is also responsible for optimizing transfusion microbiology working practice across the NBS through nationally agreed standards and procedures. Over the past 9 years, a total of 44 assays from 15 suppliers have been monitored. Five assays have been withdrawn from use as a result of identified poor performance; two hepatitis B virus surface antigen assays owing to poor sensitivity, two syphilis agglutination assays with nonspecific (false) reactive rates sustained above contract limits and one human cytomegalovirus antibody assay that persistently failed the manufacturer's quality control criteria. This approach has enabled the differentiation of genuine kit performance issues from 'natural variation' in kit performance, and local instrumentation or training issues. The NBS has been able to address the issues with suppliers much earlier and resolve minor issues before they became major problems. In addition, a lot release system has been developed and implemented, comprising a formal, centralized initial scientific assessment of each new manufacturer's lot, followed by 'delivery acceptance' testing at each site. This system helps to ensure that the evaluated minimum sensitivity and specificity of the assays is maintained from 'lot to lot'.

Chronic hepatitis B carriers found at blood donation: do they need regular follow-up?

It is recommended by the Department of Health and Social Security that hepatitis B virus (HBV) carriers found at blood donation should be followed up by specialist liver units. We attempted to do this in 74 such patients found by the Yorkshire Regional Blood Transfusion Service during a 4.5-year period. Only 32 of the patients eventually attended for further investigation and follow-up. However, 43 chronic HBV carriers found at blood donation have been followed for varying periods from 2 to 14 years, and the prognosis has been good. Although this raises the question as to whether such carriers need to be seen routinely in a specialist unit, we suggest that there are good reasons to continue to advocate this policy.

Evaluation of a combined HIV-1/2 and HTLV-I/II assay for screening blood donors.

A combined immunoassay for the simultaneous detection of antibodies to HIV-1/2 and HTLV-I/II (Bioelisa, Launch Diagnostics) has been evaluated to determine its suitability for routine use in blood screening. 84,222 donations were tested from 76,452 donors. One HIV- and 1 HTLV-1-positive donor were identified. The specificity was 99.7%, and the sensitivity for anti-HIV-1, anti-HIV-2, and anti-HTLV-1 on 173 positive sera was 100%; 2 of 25 anti-HTLV-II-positive sera were non-reactive. Although the specificity of the assay is not as high as that of HIV-1/2 kits currently in UK transfusion use, the information gained about donor HTLV antibody status makes the test an attractive alternative to them.