Blood Transfusion Centre of Slovenia, Department for Diagnostic Services, Ljubljana, Slovenia.
Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia
Blood Transfus. 2021 Jan;19(1):77-84. doi: 10.2450/2020.0120-20. Epub 2020 Oct 9.
Serological assays for the diagnosis of heparin-induced thrombocytopenia (HIT) detect both platelet-activating and platelet non-activating anti-heparin/platelet factor 4 (PF4) antibodies and have therefore a limited positive predictive value. Functional assays confirm the presence of platelet-activating antibodies but require platelets from healthy donors, whose response to patient serum can differ. Our aim was to investigate the correlation between the level of anti-heparin/PF4 antibodies, 4T score, and the extent of panel donor platelet activation in the functional assay.
In total, 38 sera from enzyme immunoassays (ELISA) positive patients were tested against panel platelets obtained from 10 healthy, randomly selected donors, using our routine flow cytometry functional test for CD62P expression. Levels of anti-heparin/PF4 antibodies from medical and surgical patients and 4T pretest probability scores (where available) were correlated with the number of activated panel platelets.
Sera with low ELISA optical density (OD) values (0.4-1) activated on average 5.6, sera with intermediate ELISA OD values (>1-2.5) activated on average 7.3, and sera with high ELISA OD values (>2.5) activated on average 8.6 out of 10 panel platelets. One serum with low 4T score did not activate donor platelets, 12 sera with intermediate 4T score activated on average 6.3 donors, 8 sera with high 4T score activated on average 8.5 panel platelets.
Sera with higher ELISA OD values activated platelets from a higher number of platelet donors, independently of patient type (medical or surgical). The average number of activated panel platelets increased with rising 4T score. Results indicate that both donor platelet reactivity and quantity of anti-heparin/PF4 antibodies affect the result of the functional assay, meaning special attention is needed in platelet donor selection when testing sera with low levels of antibodies.
用于诊断肝素诱导的血小板减少症（HIT）的血清学检测可同时检测到血小板激活和非血小板激活的抗肝素/血小板因子 4（PF4）抗体，因此其阳性预测值有限。功能检测可确认血小板激活抗体的存在，但需要来自健康供体的血小板，而患者血清对健康供体血小板的反应可能存在差异。我们的目的是研究抗肝素/PF4 抗体水平、4T 评分和功能检测中面板供体血小板激活程度之间的相关性。
共检测了 38 份酶联免疫吸附试验（ELISA）阳性患者的血清，这些血清来自 10 位随机选择的健康供体的面板血小板，使用我们常规的流式细胞术 CD62P 表达功能检测方法。将来自内科和外科患者的抗肝素/PF4 抗体水平和 4T 术前概率评分（如有）与激活的面板血小板数量相关联。
ELISA 吸光度（OD）值较低（0.4-1）的血清平均激活 10 个面板血小板中的 5.6 个，ELISA OD 值中等（>1-2.5）的血清平均激活 7.3 个，ELISA OD 值较高（>2.5）的血清平均激活 8.6 个。1 份 OD 值低的 4T 评分低的血清未激活供体血小板，12 份 OD 值中等的 4T 评分的血清平均激活 6.3 个供体血小板，8 份 OD 值高的 4T 评分的血清平均激活 8.5 个面板血小板。
ELISA OD 值较高的血清可激活来自更多供体血小板的血小板，与患者类型（内科或外科）无关。随着 4T 评分的升高，激活的面板血小板数量也增加。结果表明，供体血小板反应性和抗肝素/PF4 抗体数量都会影响功能检测的结果，这意味着在使用低抗体水平的血清进行检测时，需要特别注意血小板供体的选择。
