Development of Urinalysis Screening Criteria for Rhabdomyolysis in Acute Kidney Injury

Background: Rhabdomyolysis (RM) is the etiology in 7-10% of cases of AKI and benefits from early, aggressive volume repletion. RM as an etiology of AKI is often missed in clinical setting as it requires specific diagnostic testing (CK testing). We evaluated various criteria that could be applied to urinalysis (UA) to identify individuals at elevated likelihood of RM. Methods: A retrospective electronic chart review of adult inpatients hospitalized at the Yale New Haven Hospital was performed between January 2020-December 2022. A total of 16 screening criteria were formulated using combinations of heme (≥1+, ≥ 2+, ≥ 3+, and ≥ 4+) and RBCs (≤5, ≤10, ≤20, and ≤30) per high power field (HPF) thresholds from the closest UA prior to AKI. The accuracy was assessed using post-AKI CK>1000 U/L as the definition of rhabdomyolysis diagnosis. Results: A total of 12,273 patients were included of which 20.5% patients had serum CK levels checked after AKI. Of those, 222 (8.8%) met the diagnostic criteria for rhabdomyolysis. The median time from laboratory AKI diagnosis to CK measurement was 2.7 (0.9-6.5) days. UA criterion 1.4 (≥1 heme and ≤30 RBCs) met by 35.1% demonstrated the highest sensitivity for rhabdomyolysis. UA criterion 3.1 (≥ 3+ heme and ≤5 RBCs) met by 2.0% demonstrated a specificity of 96.7% and sensitivity of 16.7% included the highest proportion of patients with CK measurement (45.3%), and more than a quarter of those tested had levels consistent with rhabdomyolysis. Conclusions: Rhabdo-suspected patients with greater heme/RBC discrepancy on UA were more likely to be tested for serum CK levels and diagnosed with rhabdo. CK testing was uncommon under all definitions, suggesting missed rhabdomyolysis cases. Automated electronic screening of UA parameters with clinical decision support to order CK may be a viable mechanism to increase the diagnosis of rhabdo among AKI patients.