Wardenaar Floris, Ortega-Santos Carmen P, Vento Kaila, Olzinski Stephanie, Olig Jason, Kavouras Stavros, Johnston Carol
College of Health Solutions, Arizona State University, Phoenix.
J Athl Train. 2021 Apr 1;56(4):389-395. doi: 10.4085/1062-6050-0142.20.
Urine specific gravity (USG) should be measured at room temperature (20°C), but the temperature of the sample is not always considered.
To evaluate the effect of sample temperature on the measurement accuracy of a digital refractometer (DIG), manual optical refractometer (MAN), and hydrometer (HYD).
Descriptive laboratory study.
MAIN OUTCOME MEASURE(S): Urine specific gravity.
Experiment 1 (24 Brix (°Bx) samples) showed that measurements via the DIG and MAN did not differ from the reference, but HYD provided lower or inconsistent values compared with °Bx and was highly correlated with °Bx solutions (r, > = 0.89). The overall diagnostic ability of elevated USG cut-off values (≥1.020, ≥1.025, ≥1.030) was high for all tools (area under the curve >0.92). Misclassification of samples increased from 0 to 2 at 1.020 to 1 to 3 samples at cutoffs of 1.025 and 1.030 USG. Bland-Altman analysis showed that the DIG 5°C underreported slightly without reporting bias (r = -0.344, P = .13); all other plots for the DIG, MAN, and HYD showed considerably larger underreporting at higher concentrations (r = -0.21 to -0.97 with P >.02) at all temperatures. The outcomes of experiment 2 (33 fresh urine samples) using DIG 20°C as the standard demonstrated only negligible differences between the DIG and MAN at all temperatures but larger differences using the HYD.
All tools showed reporting bias compared with the °Bx solutions, which can affect the classification of low and high urine concentration at higher USG cutoff values, especially with a sample temperature of 37°C.
尿比重（USG）应在室温（20°C）下测量，但样本温度并非总是被考虑在内。
评估样本温度对数字折射仪（DIG）、手动光学折射仪（MAN）和比重计（HYD）测量准确性的影响。
描述性实验室研究。
尿比重。
实验1（24个白利度（°Bx）样本）表明，通过DIG和MAN测得的结果与参考值无差异，但与°Bx相比，HYD得出的值较低或不一致，且与°Bx溶液高度相关（r≥0.89）。所有工具对于升高的USG临界值（≥1.020、≥1.025、≥1.030）的总体诊断能力较高（曲线下面积>0.92）。在USG临界值为1.020时，样本误分类从0增加到2，在临界值为1.025和1.030时，误分类从1增加到3个样本。Bland-Altman分析表明，DIG在5°C时略有低估但无报告偏倚（r = -0.344，P = 0.13）；在所有温度下，DIG、MAN和HYD的所有其他图表在较高浓度下均显示出明显更大的低估（r = -0.21至-0.97，P>.02）。以DIG 20°C作为标准的实验2（33个新鲜尿液样本）的结果表明，在所有温度下，DIG和MAN之间仅存在微不足道的差异，但使用HYD时差异更大。
与°Bx溶液相比，所有工具均显示出报告偏倚，这可能会影响在较高USG临界值下对低尿浓度和高尿浓度的分类，尤其是在样本温度为37°C时。
