Phakdeekitcharoen Bunyong, Kreepala Chatchai, Boongird Sarinya
Division of Nephrology, Department of Medicine, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand.
J Med Assoc Thai. 2011 Nov;94(11):1337-45.
Hypokalemia, serum potassium (K) < 3.5 mEq/L, is a serious and common clinical problem. The traditional diagnosis of renal potassium losses is 24-hr urine potassium (24U(K)) > or = 20 mEq/day during hypokalemia. Immediate replacement of potassium is often required to prevent complication but may normalize serum K during 24-hr urine collection and render the test inconclusive.
The authors examined the ability of urinary indices including 24U(K), transtubular potassium gradient (TTKG), fractional excretion of potassium (FE(K)), urine potassium-creatinine ratio (U(K/Cr)) and spot U(K) and introduced urine potassium per hour during the first 8 hours (U(K)/hr) as a novel index for evaluation of hypokalemia during treatment. Any serum K level > or = 4 mEq/L during urine collection was defined as normalized serum K. In the present study, the final classification of renal K losses in non-normalized 24-hr serum K group was made when 24U(K) > or = 20 mEq/day. In normalized group, the final classification of renal or non-renal K losses was based on the majority of the results of four urine indices including TTKG, FE(K) U(K/Cr) and spot U(K).
Of 61 patients (renal:non-renal = 50:11), 51% and 18% met the criteria of normalized 24-hr and 8-hr serum K. Over all, the U(K)/hr > or = 0.9 mEq/hr can indicate renal K losses with a sensitivity of 96% and specificity of 72.7% compared with the 24U(K) > or = 20 mEq/day of 100% and 54.5%, respectively. In a subgroup of normalized 24-hr serum K, the sensitivity and specificity of U(K)/hr = 95.5% and 77.8% whereas 24U(K) = 100% and 44.4%, respectively
U(K)/hr is a new practical, simple, and reliable marker that can be applied to evaluate hypokalemic patients during treatment with comparable sensitivity and specificity with 24U(K).
低钾血症，即血清钾（K）<3.5 mEq/L，是一个严重且常见的临床问题。传统上，肾性钾丢失的诊断标准是在低钾血症期间24小时尿钾（24U(K)）≥20 mEq/天。通常需要立即补钾以预防并发症，但这可能会使血清钾在24小时尿液收集期间恢复正常，从而使检测结果无法判定。
作者研究了包括24U(K)、肾小管钾梯度（TTKG）、钾排泄分数（FE(K)）、尿钾肌酐比值（U(K/Cr)）以及随机尿钾（spot U(K)）等尿指标的能力，并引入了治疗期间最初8小时的每小时尿钾（U(K)/hr）作为评估低钾血症的新指标。尿液收集期间任何血清钾水平≥4 mEq/L被定义为血清钾恢复正常。在本研究中，24小时血清钾未恢复正常组中肾性钾丢失的最终分类是在24U(K)≥20 mEq/天时确定的。在血清钾恢复正常组中，肾性或非肾性钾丢失的最终分类基于TTKG、FE(K)、U(K/Cr)和随机尿钾这四项尿指标的多数结果。
61例患者（肾性：非肾性=50:11）中，51%和18%符合24小时和8小时血清钾恢复正常的标准。总体而言，与24U(K)≥20 mEq/天的敏感性100%和特异性54.5%相比，U(K)/hr≥0.9 mEq/hr可提示肾性钾丢失，敏感性为96%，特异性为72.7%。在24小时血清钾恢复正常的亚组中，U(K)/hr的敏感性和特异性分别为95.5%和77.8%，而24U(K)分别为100%和44.4%。
U(K)/hr是一种新的实用、简单且可靠的标志物，可用于评估低钾血症患者的治疗情况，其敏感性和特异性与24U(K)相当。
