EDTA-依賴型假性血小板減少

Ethylene Diaminete Traacetic Acid- Dependent Pseudothrombocytopenia (EDTA-PTCP)

背景：EDTA-依賴型假性血小板低下（EDTA-PTCP）是一種在體外以EDTA為抗凝劑時血小板凝集的現象，而造成在血液儀器測量下血小板呈假性低值。我們描述一個EDTA-依賴型假性血小板低下的77歲女性的個案報告，預定做全人工髖關節置換手術而住院。手術前，血小板低值與其數值不明原因的變化造成困惑與手術的延遲，一個相關的實驗被設計，結果確認病患有EDTA-依賴型假性血小板低下。因此醫生診斷為假性血小板減少並在隨後為病患進行手術。方法：我們在「UpToDate」實證醫學資料庫搜尋假性血小板減少的定義與診斷方法，並隨後設計了一個實驗，由靜脈抽血採檢後分裝五個不同的採血管，五管分別含有EDTA（第1管），檸檬酸鈉（第2管），肝素（第3管）等抗凝劑，及採新鮮全血不加任何抗凝劑（第4管），外加一ED TA管（第5管），在測量血小板數值前先孵育於37℃下20分鐘。所有檢體皆由血液自動分析儀CELL-DYN 3700測量。第1、2、3管分別於採血後0分、5分、10分、20分、30分、等時間點即時上機，同時將第1管製做抹片並觀察。結果：含抗凝劑的1-3管上機測量後可以觀察到血小板減少的狀況，檸檬酸鈉抗凝劑檢體的血小板數亦會減少，但減少的幅度明顯比另外兩管小多了。周邊血液抹片可以觀察到漸漸增大的血小板凝集。在此案例77歲婦人確認為EDTA-依賴型假性血小板低下，手術隨後展開。結論：在此類案例使用ED TA以外的抗凝劑可避免血小板凝集，但我們也發現即使是檸檬酸鈉與肝素抗凝劑可能也與血小板凝集的形成有關。似乎最好的分析方式是抽血後即刻上機而不添加任何抗凝劑。為了避免不正確的診斷與不適當的處置，EDTA-依賴型假性血小板低下應經常被視為血小板低值的可能原因之一，特別是當臨床上有不顯著的發現時，應運用適當的實驗室分析。

Background: Ethylene diaminete traacetic Acid-dependent pseudothrombocytopenia (EDTA-PTCP) is an in vitro phenomenon of platelet clumping in blood, anticoagulated with EDTA, that leads to spuriously low platelet counts by automatic hematology analyzers. We describe a case of EDTA-PTCP in a 77-year-old woman, who was admitted for total hip replacement surgery. Preoperatively, low level and unknown changes of platelet counts cause confusion and postpone of surgery. A correlative experiment was designed and the results confirmed EDTA-PTCP in the patient. The physician accordingly diagnosed as pseudothrombocytopenia and subsequently followed by surgery. Methods: We searched 'UpToDate' Evidence-Based Medicine database for definition and diagnostic approach o f pseudothrombocytopenia, and consequently designed an experiment in this case. We collected 5 blood specimens by venepuncture in different tubes each containing EDTA(tube1), sodium citrate(tube2), heparin(tube3) anticoagulants, and freshly drawn samples without any anticoagulant(tube 4), plus one more EDTA tube(tube 5) with 20 minutes, 37℃ incubation prior to platelet measurement. All tubes were measured with a CELL-DYN 3700 hematology analyzer; tube1, 2, 3 were measured at times 0, 5, 10, 20, 30 minutes from venepuncture. Immediately after analysis at these respective times, slides of tube1 sample were also made and inspected. Tube 4 was measured directly as fresh whole blood put in, and Tube 5 were measured immediately after 37℃, 20 minutes incubation. Results: Three agents(tube1-3) were observed to induce a decreasing platelet count. Platelet counts in the sodium citrate sample also fell, yet this appeared to be considerably less than the other two specimens. Increased clumping could be observed on the PB smears through microscopic examination. The 77-yearold woman in this case was confirmed EDTA-PTCP. The operation was subsequently performed. Conclusions: Platelet clumping could be avoided in such cases by the use of anticoagulants other than EDTA, but we also found even citrate, and heparin have been implicated as anticoagulants that may cause platelet clumping. The best analytic course appears to be immediately running the freshly drawn samples [11] without the use of anticoagulants at all. To avoid incorrect diagnoses and inappropriate treatment, EDTA-PTCP should always be considered as a possible cause of low platelet count, especially in cases of inconspicuous clinical findings. Appropriate laboratory analysis should be applied.