Berkshire Medical Center, Internal Medicine, Pittsfield, Massachusetts, USA.
J Clin Lab Anal. 2010;24(6):426-30. doi: 10.1002/jcla.20424.
Urine specific gravity (USG) is often used by clinicians to estimate urine osmolality. USG is measured either by refractometry or by reagent strip.
We studied the correlation of USG obtained by either method with a concurrently obtained osmolality.
Using our laboratory's records, we retrospectively gathered data on 504 urine specimens on patients on whom a simultaneously drawn USG and an osmolality were available. Out of these, 253 USG's were measured by automated refractometry and 251 USG's were measured by reagent strip. Urinalysis data on these subjects were used to determine the correlation between USG and osmolality, adjusting for other variables that may impact the relationship. The other variables considered were pH, protein, glucose, ketones, nitrates, bilirubin, urobilinogen, hemoglobin, and leukocyte esterase. The relationships were analyzed by linear regression.
This study demonstrated that USG obtained by both reagent strip and refractometry had a correlation of approximately 0.75 with urine osmolality. The variables affecting the correlation included pH, ketones, bilirubin, urobilinogen, glucose, and protein for the reagent strip and ketones, bilirubin, and hemoglobin for the refractometry method. At a pH of 7 and with an USG of 1.010 predicted osmolality is approximately 300 mosm/kg/H(2)O for either method. For an increase in SG of 0.010, predicted osmolality increases by 182 mosm/kg/H(2) O for the reagent strip and 203 mosm/kg/H(2)O for refractometry. Pathological urines had significantly poorer correlation between USG and osmolality than "clean" urines.
In pathological urines, direct measurement of urine osmolality should be used.
尿液比重（USG）常被临床医生用于估计尿液渗透压。USG 可通过折射仪或试剂条测量。
我们研究了两种方法获得的 USG 与同时获得的渗透压之间的相关性。
使用我们实验室的记录，我们回顾性地收集了 504 份尿液样本的数据，这些样本的患者同时进行了 USG 和渗透压检测。其中，253 个 USG 通过自动折射仪测量，251 个 USG 通过试剂条测量。对这些患者的尿液分析数据进行了分析，以确定 USG 与渗透压之间的相关性，同时调整了可能影响这种关系的其他变量。考虑的其他变量包括 pH 值、蛋白质、葡萄糖、酮体、硝酸盐、胆红素、尿胆原、血红蛋白和白细胞酯酶。使用线性回归分析这些关系。
本研究表明，两种试剂条和折射仪获得的 USG 与尿液渗透压的相关性约为 0.75。影响相关性的变量包括 pH 值、酮体、胆红素、尿胆原、葡萄糖和蛋白质（试剂条）和酮体、胆红素和血红蛋白（折射仪）。在 pH 值为 7 且 USG 值为 1.010 时，两种方法的预测渗透压约为 300 mosm/kg/H(2)O。试剂条的 SG 增加 0.010 时，预测渗透压增加 182 mosm/kg/H(2)O，折射仪增加 203 mosm/kg/H(2)O。病理性尿液的 USG 与渗透压之间的相关性明显低于“清洁”尿液。
在病理性尿液中，应直接测量尿液渗透压。
