Many Emergency Department patients with acute rhabdomyolysis are admitted to hospital to observe for development of renal failure. We examined factors associated with a normal admission serum creatinine, and a normal post-hydration creatinine, to determine which patients had low risk of development of renal failure.

Methods

This is a retrospective study of 144 consecutive patients with a diagnosis of rhabdomyolysis seen in our Emergency Department over 44 months. A 'normal serum creatinine' was defined as less than 1.5 mg/dl (133 μum/l). Laboratory data included the initial and peak creatine kinase (CK), the anion gap, calcium, phosphate, potassium, blood urea nitroben (BUN), white blood cell count (WBC), urine toxicology screen, and hematocrit. A second hematocrit collected following hydration was compared with the first to approximate the percentage of initial volume depletion. A second creatinine was also taken following hydration (median 10 hours after admission). Patients with obvious renal insufficiency defined as a creatinine > 4 mg/dl (354 μm/l) and patients with peak CK < 1000 were excluded. Multivariate logistic regression analysis was performed using small STATA 7.0. For continuous variables, data were dichotomized based on an upper limit of normal values (phosphate, potassium, BUN) or low limit (calcium); and median values of the anion gap, hematocrit, percentage decrease in hematocrit, WBC, and CK.

Results

Significant independent predictors of a normal first creatinine are presented in Table 1. The most powerful independent predictor of a normal post-hydration creatinine was a normal admission creatinine (odds ratio [OR] = 31, confidence interval [CI] = 6.6-145, P = 0.0001). An elevated BUN and a CK greater than 10,000 were negative predictors of a normal second creatinine (OR = 0.20, CI = 0.06-0.65, P = 0.008, and OR = 0.21, CI = 0.07-0.61, P = 0.004).

Table 1
Full size table

Conclusion

A normal admission creatinine was associated with WBC < 11.0, the absence of cocaine or amphetamine, less than 18% volume depletion, a normal BUN and a normal calcium. A normal first creatinine was a very strong predictor of a normal second creatinine after hydration. This suggests that otherwise healthy patients with uncomplicated rhabdomyolysis and a normal first creatinine who can hydrate themselves orally may be safely discharged from acute emergency care after correction of volume deficits.