Lew S W, Bosch J P
Department of Medicine, George Washington University Medical Center, Washington, DC.
J Am Soc Nephrol. 1991 Oct;2(4):856-65. doi: 10.1681/ASN.V24856.
Thirty-seven young healthy subjects with normal renal function were studied to assess the quantitative effect of protein intake on creatinine clearance. A standard 24-h urine collection and blood sample at the end of the collection were obtained for creatinine and urea concentrations. Correlations between creatinine clearance and urinary urea nitrogen excretion (r = 0.8; P less than 0.0001) and calculated protein intake (r = 0.8; P less than 0.0001) were observed. A significant relationship between creatinine clearance and urea nitrogen excretion was also demonstrated in 28 elderly healthy subjects and 33 patients with renal disease. To demonstrate a cause and effect between urea nitrogen excretion and creatinine clearance in healthy subjects, 18 of the 37 healthy subjects repeated the 24-h urine collection and blood sample after ingesting 5 g of urea in addition to their usual diet. Mean urinary urea nitrogen excretion increased from a mean value of 9.8 +/- 4.0 to 11.8 +/- 4.0 g/day. There was a strong correlation between the changes in urea nitrogen excretion and the changes in creatinine clearance. In acute studies with oral protein loading, there was a significant correlation between creatinine clearance and urinary urea nitrogen excretion. It was concluded that protein intake has a direct and quantitative effect on creatinine clearance in healthy subjects. In normal humans, it is likely that GFR is not a fixed function. Thus, a low creatinine clearance is not a categorical sign of renal disease. A low creatinine clearance adjusted for urea nitrogen excretion may be a useful clinical tool to assess renal function.
对37名肾功能正常的年轻健康受试者进行了研究，以评估蛋白质摄入量对肌酐清除率的定量影响。在收集24小时标准尿液的末期采集血样，测定肌酐和尿素浓度。观察到肌酐清除率与尿尿素氮排泄量之间的相关性（r = 0.8；P < 0.0001）以及与计算得出的蛋白质摄入量之间的相关性（r = 0.8；P < 0.0001）。在28名老年健康受试者和33名肾病患者中也证实了肌酐清除率与尿素氮排泄之间存在显著关系。为了证明健康受试者中尿素氮排泄与肌酐清除率之间的因果关系，37名健康受试者中的18人在其日常饮食基础上额外摄入5克尿素后，重复进行了24小时尿液收集和血样采集。尿尿素氮排泄的平均值从9.8±4.0克/天增加到11.8±4.0克/天。尿素氮排泄量的变化与肌酐清除率的变化之间存在很强的相关性。在口服蛋白质负荷的急性研究中，肌酐清除率与尿尿素氮排泄之间存在显著相关性。得出的结论是，蛋白质摄入量对健康受试者的肌酐清除率有直接的定量影响。在正常人体内，肾小球滤过率（GFR）可能不是一个固定的功能。因此，低肌酐清除率并非肾病的绝对标志。根据尿素氮排泄量调整后的低肌酐清除率可能是评估肾功能的一种有用的临床工具。
