[HEMA]假性血小板低下症(Pseudothrombocytopenia)

By HCH_IM_CR |

2009年12月22日 星期二

Platelet clumping in EDTA

假性血小板低下症(Pseudothrombocytopenia)，Dr.韋在晨會提出的Case，來作一下整理。

假性的血小板數目低下有部分是因為常規血球計數檢查中加入的EDTA導致血小板黏著在一起 (platelet clumping)而造成，機率約為1/1000，且與病患本身所患的疾病種類完全無關。診斷必須藉由週邊血液的抹片來加以確認。

UpToDate:
Pseudothrombocytopenia — The platelet count can be falsely low in a number of clinical situations:→許多臨床狀況都會造成血小板假性低下。

>If anticoagulation of the blood sample is inadequate, the resulting thrombin-induced platelet clumps can be counted as leukocytes by automated cell counters. In these circumstances, the WBC count is rarely increased by more than 10 percent and there is usually an associated spurious thrombocytopenia [10]. →血液在試管內沒有充分和抗凝血劑作用，可能會造成thrombin-induced platelet clumps，聚集的血小板團會被計數器當作是一顆白血球，因此白血球數量甚至有時候上升超過10%。

>Approximately 0.1 percent of normal subjects have EDTA- dependent agglutinins which can lead to platelet clumping and spurious thrombocytopenia and spurious leukocytosis. This is thought to result from a "naturally occurring" platelet autoantibody directed against a normally concealed epitope on the platelet membrane glycoprotein (GP) IIb/IIIa, which becomes exposed by EDTA-induced dissociation of GP IIb/IIIa [11-17]. Pseudothrombocytopenia then occurs because EDTA is the anticoagulant employed in the tubes used for routine complete blood counts. →正常人有1/1000會發現EDTA- dependent agglutinins引起的platelet clumping。

(機轉請讀UpToDate: Thrombocytopenia induced by glycoprotein IIb/IIIa inhibitors)

>Pseudothrombocytopenia can also occur after the administration of the murine monoclonal antibody abciximab, which is directed against the GP IIb/IIIa receptor [18]. EDTA-induced platelet clumping can be diagnosed by examination of the peripheral smear. This is an established routine for laboratory technologists, but sometimes the physician only receives the report of the falsely low platelet count number, without the note about clumping or a repeat count in a non-EDTA anticoagulant. → 給了abciximab (ReoPro®) 也可能造成假性血小板低下。ETDA引起的血小板團可藉由檢查周邊血液(PB smear)確診。對醫檢師來說應該是很常規的事情，但有時候臨床醫師只看報告就認定是血小板低下，卻忘了可能是platelet clumping或再做一次非EDTA抗凝劑的血球計數來確認。

>If platelet clumping is observed, the platelet count is repeated using heparin or sodium citrate as an anticoagulant. If citrate is used, one should remember to correct the platelet count for dilution caused by the amount of citrate solution used; no such correction is needed for heparin. Alternatively, one can use freshly-shed non-anticoagulated blood pipetted directly into platelet counting diluent fluid. →EDTA不行就換其他凝血劑，換heparin or sodium citrate試試看。藍頭PT/aPTT試管用Sodioum Citrate當抗抗凝血劑，不過因為Citrate的量會輕微稀釋血液(一管內約0.3-0.4ml)，記得要矯正過。

下次看到血小板低下，不妨用藍頭管送個CBC吧~~~! !