Understanding the limitations of the urinalysis in renal and GU trauma is central to clinical decision-making. Urinalysis should be performed on all abdominal trauma patients. If renal or GU injury is suspected, the first spontaneously voided sample of urine is essential to identify hematuria, as this has the highest sensitivity, before fluid administration or diuresis can obscure its presence.38,61 Offering a urinal or bedpan after initial stabilization can help facilitate this. Hematuria is defined as more than 5 red blood cells seen per high-power field. This is generally ascertainable by urine dipstick, although differing brands may have variable specificity and sensitivity, with a false-negative rate up to 10% reported.4,62 Differentiating between gross and microscopic hematuria is important, with most experts putting the break point between the two at 30 to 50 red cells per high-power field.62
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