Section of Clinical Pathology, Department of Companion Animal Clinical Studies, Faculty of Veterinary Science, University of Pretoria, Pretoria, South Africa.
Department of Companion Animal Clinical Studies, Faculty of Veterinary Science, University of Pretoria, Pretoria, South Africa.
Vet Clin Pathol. 2020 Sep;49(3):407-416. doi: 10.1111/vcp.12892. Epub 2020 Aug 31.
Veterinary facilities might use multiple refractometers and individuals to measure urine specific gravity (USG). Previous comparison studies show conflicting results. Furthermore, the clinical significance of measurement differences and interobserver variabilities has not been assessed.
We aimed to determine statistically and clinically significant differences between four refractometers in measuring canine USG and subsequent categorization of urine concentrations and azotemia and determine the variability between different observers performing USG measurements.
Fifty-nine specimens were included for the USG measurements with four refractometers by different observers. Each refractometer pair was compared using Spearman's rank correlation, Bland-Altman difference plots, and Deming regression analyses. Calculated bias was compared to set performance goals. Interobserver agreement was evaluated, and intraclass correlation coefficients were used to determine differences in the categorization of urine concentrations and azotemia (prerenal or renal).
There was excellent correlation (r = .99-1.00) between refractometers. All comparisons involving R4 showed significant constant and proportional biases. Mean bias met the clinical performance goals for all refractometers, except for comparisons with R4, where up to 17 results were outside the allowable bias. There was almost perfect agreement (r = .999) between observers and excellent agreement (ICC = .96-.99) for the classification of urine concentrations. In azotemic patients (22%), there was perfect agreement (ICC = 1.00) for the categorization of azotemia.
In most cases, three of the refractometers evaluated in this study can be used interchangeably at all USG values, without affecting clinical decision-making. Multiple observers did not significantly affect decision-making.
兽医设施可能会使用多个折射计和人员来测量尿液比重（USG）。以前的比较研究显示出相互矛盾的结果。此外，尚未评估测量差异和观察者间变异性的临床意义。
我们旨在确定四种折射计在测量犬 USG 方面的统计学和临床显著差异，以及随后对尿液浓度和氮血症的分类，并确定不同观察者进行 USG 测量的可变性。
由不同观察者使用四台折射计对 59 个标本进行 USG 测量。使用 Spearman 等级相关、Bland-Altman 差值图和 Deming 回归分析比较每对折射计。将计算出的偏差与设定的性能目标进行比较。评估观察者间的一致性，并使用组内相关系数确定尿液浓度和氮血症（肾前或肾性）分类的差异。
折射计之间存在极好的相关性（r = .99-1.00）。所有涉及 R4 的比较均显示出显著的恒定和比例偏差。除与 R4 的比较外，所有折射计的平均偏差均符合临床性能目标，在这些比较中，多达 17 个结果超出了允许的偏差。观察者之间存在几乎完美的一致性（r = .999），对于尿液浓度的分类存在极好的一致性（ICC = .96-.99）。在氮血症患者（22%）中，氮血症的分类存在完美的一致性（ICC = 1.00）。
在大多数情况下，本研究评估的三种折射计可以在所有 USG 值下互换使用，而不会影响临床决策。多个观察者不会显著影响决策。
