肾性与非肾性低钾血症的实验室诊断

Laboratory tests of renal and extrarenal hypokalemia

目的探讨以简单易行的指标来区别肾性、非肾性低钾血症。方法低钾血症患者39例，包括肾性低钾血症24例，非肾性低钾血症15例。在低钾发作时，补充钾盐之前收集随机尿、血标本，对所得的钾滤过排泄分数（FEK）、尿钾肌酐比率（尿K^＋／Cr）、跨管钾梯度（TTKG）和尿K^＋／Na^＋进行分析，获得区别肾性、非肾性低钾血症的有效指标及相应切点值。结果肾性与非肾性低钾血症的FEK、尿K^＋／Cr和TTKG有统计学差异（P〈0．01），前者明显高于后者。区别两者的FEK、尿K^＋／Cr切点值分别为14％和5（前者灵敏度、特异度均为100％；后者为96％、87％），且两指标呈线性正相关，相关系数（y=0．94，P〈0．01）。结论FEK、尿K^＋／Cr是区别肾性、非肾性低钾血症的有效指标，当FEK〉14％或尿K^＋／Cr〉5时考虑钾从肾脏丢失过多。

Objective To make a distinction between renal and extrarenal hypokalermia with some simple and feasible indexes. Method 39 patients with hypokalemia were studied, including 24 with renal hypokalemia and 15 with extrarenal hypokalemia. Before potassium therapy, a spot urine and blood sample were collected randomly during hypokalemia. Then we calculated FEK（fractional excretion of potassium）, urine potassium-creatinine ratio, TTKG（transtubular potassium concentration gradient）, urine potassium-natrium ratio, and obtaimed the valuable indexes and the relevant cutoff values to differentiate between renal and extrarenal hypokalemia. Results FEK, urine potassium-creatinine ratio and TTKG were significantly different the renal and extrarenal hypokalemia（P〈0. 01）. The values of the former group were higher than that of the latter. The cutoff values of FEK and urine potassium-creatinine ratio between renal and extrarenal hypokalemia were 14% and 5 respectively （both the sensitivity and specificity of the former were 100%, the latter 96% and 87%）, and the two indexes were positively linearly correlated with each other. Conclusions FEK and urine potassiumcreatinine ratio are valuable indexes to differentiate the renal and extrarenal hypokalemia. When FEK is over 14% or urine potassium-creatinine ratio is over 5, overexcretion of potassium from kidney is considered.