How do I interpret sediment, specific gravity, and dipstick findings on a veterinary urinalysis?

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A complete urinalysis integrates three components — urine specific gravity (USG), dipstick chemistry, and sediment examination — and each must be interpreted in the context of the others and the patient's clinical presentation. 1 --- Urine Specific Gravity USG is measured by refractometer at room temperature before centrifugation, unless the sample is discolored or turbid, in which case testing on the supernatant is preferable to avoid interference. 3 In chinchillas, USG measured by refractometer before centrifugation does not differ significantly from post-centrifugation values, so pre-centrifugation measurement is acceptable in that species; USG ranges from 1.014 to >1.060 in clinically normal chinchillas, with 41% of samples at ≥1.050. 5 For dogs and cats, USG is a critical modifier of dipstick protein results — a positive dipstick protein finding in dilute urine carries different clinical weight than the same result in concentrated urine, because USG directly influences the apparent protein concentration. 18 --- Dipstick Chemistry Dipstick results are semiquantitative and colorimetric, making them vulnerable to interference from sample color, turbidity, and temperature. Discolored or turbid samples can render reagent strips unreadable, as seen with dark red hemoglobinuric urine where pH, glucose, ketones, and urobilinogen strips become uninterpretable due to color interference. 23 Performing dipstick analysis on supernatant after centrifugation mitigates this problem. 3 For protein, dipstick results cannot be used alone to predict the urine protein-to-creatinine ratio (UPCR). Within any given dipstick protein category, USG does not allow accurate prediction of UPCR in dogs. 4 A calculated dipstick urine protein-to-USG ratio (DUR) improves on raw dipstick protein alone: in dogs, a DUR cutoff of 1.4 detects a UPCR >0.5 with sensitivity 89%, specificity 83%, positive predictive value 96%, and negative predictive value 63%; in cats, a DUR cutoff of 2.1 detects a UPC