Thurlow V, Ozevlat H, Jones S A, Bailey I R
Department of Chemical Pathology, Princess Royal University Hospital, Farnborough Common, Nr Orpington, Kent BR6 8ND, UK.
Ann Clin Biochem. 2005 May;42(Pt 3):196-9. doi: 10.1258/0004563053857761.
Thrombocytosis is one of several pre-analytical factors which contribute to spuriously high serum potassium concentrations, yet there is little published data to guide analysts in the selection of a specific platelet count threshold above which serum potassium results become unreliable. We have studied the sensitivity and specificity of blood platelet count as a predictor of false elevations in potassium.
Paired serum and plasma potassium measurements together with full blood count were performed for 300 patients. All samples were stored at room temperature and analysed within 4 h of collection. The difference between serum and plasma potassium was plotted against blood platelet count.
When the difference (serum-plasma) in potassium concentration was plotted against platelet count, there was a direct linear relationship. Blood platelet counts of >500 x 10(9)/L will detect elevations in serum relative to plasma potassium of >0.5 mmol/L, with a sensitivity of 71% and a specificity of 89%.
It is recommended that where blood platelet count is above 500 x 10(9)/L, potassium measurements should be repeated using lithium heparin plasma. When serum potassium results of >5.4 mmol/L are obtained, it is our policy to check the platelet count if a sample is available before reporting results. If available and above 500 x 10(9)/L, potassium results are withheld and plasma requested.
血小板增多症是导致血清钾浓度假性升高的几种分析前因素之一，但几乎没有公开数据可指导分析人员选择一个特定的血小板计数阈值，高于该阈值血清钾结果就变得不可靠。我们研究了血小板计数作为钾假性升高预测指标的敏感性和特异性。
对300例患者进行了血清和血浆钾的配对测量以及全血细胞计数。所有样本均在室温下保存，并在采集后4小时内进行分析。将血清和血浆钾的差值与血小板计数进行绘图。
当将钾浓度的差值（血清 - 血浆）与血小板计数绘图时，存在直接的线性关系。血小板计数>500×10⁹/L时，可检测出血清相对于血浆钾升高>0.5 mmol/L，敏感性为71%，特异性为89%。
建议在血小板计数高于500×10⁹/L时，应使用肝素锂血浆重复测量钾。当获得血清钾结果>5.4 mmol/L时，我们的政策是在报告结果前，如果有样本可用，检查血小板计数。如果可用且高于500×10⁹/L，则扣留钾结果并要求提供血浆。
