Urinalysis is an inadequate screen for rhabdomyolysis

Hematuria by urine dipstick with absent red blood cells (RBCs) on microscopy is indicative of rhabdomyolysis. We determined the sensitivity of this classic urinalysis (UA) finding in the diagnosis of rhabdomyolysis.

We conducted a retrospective electronic medical record review of patients with a primary or secondary diagnosis of rhabdomyolysis with a creatine phosphokinase (CPK) greater than 1000 IU/L and a UA within the first 24 hours. Data were collected using a standardized data form, and a blinded panel of 3 emergency medicine physicians reviewed selected cases. Sensitivity and 95% confidence intervals (CIs) were calculated for detection of rhabdomyolysis by UA.

During the study period, 1796 patients were diagnosed with rhabdomyolysis, of whom 228 met inclusion criteria. The mean peak CPK was 27509 IU/L. One hundred ninety-five (86%) had a urine dip-positive for blood. However, only 94 patients (41%) had a positive urine dip and negative microscopic hematuria, resulting in a sensitivity of 41% (95% CI, 35%-47%). In a subset of 66 patients (29%) with more severe rhabdomyolysis (initial CPK, ≥10000 IU/L; mean CPK, 53365 IU/L), UA had a sensitivity of 55% (95% CI, 43%-67%). Broadening the definition of negative microscopy from 0 to 3 RBCs to less than 10 RBCs only increased the sensitivity to 79% (95% CI, 73%-83%).

The combination of a positive urine dip for blood and negative microscopy is an insensitive test for rhabdomyolysis, and the absence of this finding should not be used to exclude the diagnosis.