Tvedten H W, Ouchterlony H, Lilliehöök I E
a Clinical Sciences, Faculty of Veterinary Medicine and Animal Sciences , Swedish University of Agricultural Sciences , Tjalinge 29, Vange , Sweden.
N Z Vet J. 2015 Sep;63(5):254-9. doi: 10.1080/00480169.2014.1002553. Epub 2015 Jun 8.
To compare the performance of five refractometers for determination of urine specific gravity in cats and dogs, with reference to weight of total solids and pycnometer analysis.
Urine samples from 27 cats and 31 dogs submitted for routine urinalysis were included. Urine specific gravity was determined with five refractometers. Four were optical, hand-held refractometers with a temperature compensation method and one was a digital model. Urine was dried to determine the precise weight of total solids. The total solids (g/L) were converted to an estimated specific gravity by division with 2.33. Urine specific gravity of four feline and seven canine samples were analysed with a pycnometer. Limits of agreement analysis was used to evaluate the agreement between specific gravity (analysed as specific gravity minus 1) measured by the refractometers and estimated from dried total solids, or pycnometer results.
The five refractometers reported clearly different results from each other. Proportional negative bias was noted for refractometer results compared to estimated specific gravity from total solids and a constant negative bias compared to pycnometer results. The two refractometers designed for cat urine reported similar and lowest specific gravity results with a mean negative bias of 0.007 and 0.008 units compared to estimated specific gravity from total solids, and a mean negative bias of 0.006 units compared to pycnometer results.
Refractometer results did not increase consistently with increasing urine specific gravity compared to reference methods or to other refractometers. Two feline refractometers reported consistently lower specific gravity results than reference methods and other refractometers.
Because of this imprecision, veterinarians should not use precise cut off values such as 1.030 or 1.035 for evaluation of renal concentrating ability in dogs and cats. Veterinarians should consider the variability of refractometric specific gravity results in their clinical assessment. Two feline refractometers appeared to report falsely low specific gravity results.
参照总固体重量和比重瓶分析法，比较五种折射仪测定猫和狗尿液比重的性能。
纳入27只猫和31只狗用于常规尿液分析的尿液样本。用五种折射仪测定尿液比重。其中四种是光学手持式折射仪，采用温度补偿法，一种是数字模型折射仪。将尿液烘干以确定总固体的精确重量。通过除以2.33将总固体（克/升）换算为估计比重。用比重瓶分析四只猫和七只狗的尿液样本的比重。采用一致性界限分析来评估折射仪测得的比重（分析为比重减去1）与根据烘干总固体估算的比重或比重瓶结果之间的一致性。
五种折射仪报告的结果彼此明显不同。与根据总固体估算的比重相比，折射仪结果存在比例性负偏差；与比重瓶结果相比，存在恒定负偏差。两款专为猫尿液设计的折射仪报告的比重结果相似且最低，与根据总固体估算的比重相比，平均负偏差分别为0.007和0.008单位，与比重瓶结果相比，平均负偏差为0.00
