![]() However, to our knowledge, expected changes in USG attributable to glucose in dog and cat urine have not been evaluated. 1 For example, a canine urine sample with a USG of 1.025 without glucose would have a USG of approximately 1.035 if 2,000 mg of glucose/dL was present, and interpretation of renal concentrating ability would differ substantially between these 2 results. 8 The addition of 1 g of glucose/dL is expected to change the specific gravity of water by 0.003 to 0.005. 7 Because of the perception that urine glucose causes a false elevation in USG, it has been recommended to interpret USG in relation to the presence and amount of urine glucose. The ability to accurately evaluate urine concentrating ability in diabetic patients is extremely important because many have concurrent disorders. Conditions that commonly cause glucosuria are diabetes mellitus and primary renal glucosuria. The presence of glucose in urine has the potential to affect USG measurements. A strong linear correlation for human urine exists between urine osmolality and USG as measured by refractometry in samples that do not contain protein or glucose. 5 The amount of refraction can be affected by solute concentration, chemical composition of the solute, and temperature. 2–4 For refractometers, weight of a solution is not measured instead, it is estimated on the basis of refraction of light. Use of urine test strips to determine USG is not recommended because of poor reliability. Refractometers typically are used in clinical settings for estimation of USG. In comparison, specific gravity represents the ratio of the weight of a solution to the weight of an equal volume of water. Osmolality is a measure of the number of dissolved particles in a fluid. However, because of the ease of use, USG is most commonly used to evaluate renal concentrating ability. Generally, osmolality is considered a more exact measurement of urine concentration than is specific gravity. Measurement of urine concentration is an important part of a urinalysis and crucial to differentiation of prerenal and renal azotemia. The USG that distinguishes prerenal and renal azotemia in dogs (USG = 1.030) and cats (USG = 1.040) is indicated for each species (dashed line). ![]() Each symbol represents mean results for the unaltered, undiluted urine pool and the pooled urine with various concentrations of glucose (50, 150, 300, 600, 1,200, and 2,400 mg/dL). Urine within a specified USG range was pooled (5 pools/range for dogs and 2 to 5 pools/range for cats). Graphs of the relationship between the glucose concentration and mean USG for pooled dog (A) and cat (B) urine samples with various USGs. ![]() Graphs of the relationship between the USG of unaltered pooled cat urine and the difference in USG attributable to the addition of glucose to create urine samples with glucose concentrations of 50 (A), 150 (B), 300 (C), 600 (D), 1,200 (E), and 2,400 (F) mg/dL. A relationship was considered significant at a value of P < 0.05 as determined by use of linear regression analysis. The line of values with no difference is indicated (dotted line). Each circle represents results for a single sample, and the line represents the linear regression line. Graphs of the relationship between the USG of unaltered pooled dog urine and the difference in USG attributable to the addition of glucose to create urine samples with glucose concentrations of 50 (A), 150 (B), 300 (C), 600 (D), 1,200 (E), and 2,400 (F) mg/dL.
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