Effect of residual platelets in frozen-thawed plasma on results of dilute Russell's viper venom time assay for lupus anticoagulant testing

OBJECTIVES

To determine the impact of residual platelets on dilute Russell's viper venom time (DRVVT) assay in frozen-thawed plasma submitted for lupus anticoagulant (LAC) testing.

METHODS

We measured platelet counts in frozen-thawed samples submitted for LAC testing and evaluated the association between platelet count and the DRVVT screening time and ratios. We also spiked platelets into a LAC-positive sample to observe the effect on the DRVVT.

RESULTS

Progressive increase in platelet count resulted in a statistically significant shortening of the DRVVT assay results on plasma after 1 freeze-thaw cycle. A similar effect was noted on the LAC-positive sample.

CONCLUSIONS

Residual platelets in plasma samples result in shortening of DRVVT assay after 1 freeze-thaw cycle. This may result in a false-negative LAC test result.

Off-the-shelf cryopreserved platelets for the detection of HIT and VITT antibodies

Heparin-induced thrombocytopenia (HIT) is suspected much more often than it is confirmed. Technically simple platelet factor 4 (PF4)-polyanion enzyme-linked immunosorbent assays (ELISAs) are sensitive but nonspecific. In contrast, accurate functional tests such as the serotonin release assay, heparin-induced platelet activation assay, and PF4-dependent P-selectin expression assay require fresh platelets and have complex assay end points, limiting their availability to specialized reference laboratories. To enable broad deployment of functional testing, we sought to extend platelet viability significantly by optimizing storage conditions and developed a simple functional assay end point by measuring the release of a platelet α-granule protein, thrombospondin-1 (TSP1), in an ELISA format. Platelet cryopreservation conditions were optimized by freezing platelets at controlled cooling rates that preserve activatability. Several-month-old cryopreserved platelets were treated with PF4 or heparin and were evaluated for their ability to be activated by HIT and vaccine-induced immune thrombotic thrombocytopenia (VITT) antibodies in the TSP1 release assay (TRA). HIT and spontaneous HIT patient samples induced significantly higher TSP1 release using both PF4-treated (PF4-TRA) and heparin-treated cryopreserved platelets relative to samples from patients suspected of HIT who lacked platelet-activating antibodies. This latter group included several patients that tested strongly positive in PF4-polyanion ELISA but were not platelet-activating. Four VITT patient samples tested in the TRA activated PF4-treated, but not heparin-treated, cryopreserved platelets, consistent with recent data suggesting the requirement for PF4-treated platelets for VITT antibody detection. These findings have the potential to transform the testing paradigm in HIT and VITT, making decentralized, technically simple functional testing available for rapid and accurate in-hospital diagnosis.

A prospective, blinded study of a PF4-dependent assay for HIT diagnosis

Heparin-induced thrombocytopenia (HIT) is a life-threatening, prothrombotic, antibody-mediated disorder. To maximize the likelihood of recovery, early and accurate diagnosis is critical. Widely available HIT assays, such as the platelet factor 4 (PF4) heparin enzyme-linked immunosorbent assay (ELISA) lack specificity, and the gold-standard carbon 14-labeled serotonin release assay (SRA) is of limited value for early patient management because it is available only through reference laboratories. Recent studies have demonstrated that pathogenic HIT antibodies selectively activate PF4-treated platelets and that a technically simpler assay, the PF4-dependent P-selectin expression assay (PEA), may provide an option for rapid and conclusive results. Based upon predefined criteria that combined 4Ts scores and HIT ELISA results, 409 consecutive adults suspected of having HIT were classified as disease positive, negative, or indeterminate. Patients deemed HIT indeterminate were considered disease negative in the primary analysis and disease positive in a sensitivity analysis. The ability of PEA and SRA to identify patients judged to have HIT was compared using receiver operating characteristic curve statistics. Using these predefined criteria, the diagnostic accuracy of PEA was high (area under the curve [AUC], 0.94; 95% confidence interval [CI], 0.87-1.0) and similar to that of SRA (AUC, 0.91; 95% CI, 0.82-1.0). In sensitivity analysis, the AUCs of PEA and SRA were also similar at 0.88 (95% CI, 0.78-0.98) and 0.86 (95% CI, 0.77-0.96), respectively. The PEA, a technically simple nonradioactive assay that uses ∼20-fold fewer platelets compared with the SRA, had high accuracy for diagnosing HIT. Widespread use of the PEA may facilitate timely and more effective management of patients with suspected HIT.

Latex allergy: collaborative nursing research using a consortium model

Nursing research, a recognized component of the CNS role, is difficult to develop in practice. Collaborative research is frequently recommended as a way to promote research activity by advanced practice nurses. Although most collaborative nursing research involves cooperation between academic and clinical nurses or within nursing organizations that exist for the purpose of conducting research, a regional nursing consortium can successfully carry out research activities. An investigation into the incidence and nature of latex allergy in children with myelodysplasia grew out of the education, mutual support, and advocacy activities of a regional clinical consortium. This article shares the research process, the obstacles encountered, and the strategies employed to identify, investigate, and use new nursing knowledge.

Children at risk: latex allergy and spina bifida

A collaborative study conducted by nurse coordinators at five centers for children with spina bifida (myelodysplasia) identifies the increased incidence of allergies to latex products--gloves, balloons, and catheters--in this population. Reports from 185 families or adult patients with spina bifida on a questionnaire developed by the nurse coordinators describe the sample characteristics and history to allergies. Statistical analysis concludes that children with spina bifida have a higher incidence of allergies to latex products at 20.4% than the controls at 1.1%. Patient age and the presence of shunted hydrocephalus also correlated positively with latex allergy. The increased risk in this population for latex allergy and the life-threatening reactions (anaphylaxis) have implications for patient, family, and professional education.