Urinalysis is an important part of the evaluation of any renal disorder.It is very simple, easy to perform and gives quick and valuable information. Out of the whole array of information, lets concentrate on the test that need to be done and are useful for diagnosing and managing rhabdomyolysis
Urine volume - ask about this in the history as it may give an idea about the renal involvement while you wait for the Creatinine. Of course it is helpful in monitoring response to fluids and recovery of function.
Color of urine - the myoglobin released from the muscles, turns the urine brown or red due to the heme content.
Ph of urine - Its useful to check Ph as myoglobin has shown to precipitate when Ph drops below 5.5. So check this initially and start with aggressive fluid resuscitation. recheck the Ph after 2-4 L boluses ,and if its still less than 7 , infusing bicarbonate will help increase the urine Ph and prevent precipitation of myoglobin in the tubules.
Blood & RBC count - it is well known to everyone that the urine is positive for blood and negative for RBCs( or has less than 5 cells/hpf) . The dipstix we use is sensitive for picking heme protein and myoglobin breaks down into heme, so is the positive finding of blood ,with no RBC s under the microscope. So in this scenario we assume its due to myoglobin.
Casts - finding of casts are useful diagnostically, as they are in any other case of AKI. In case of rhabdomyolysis, the casts are formed as a result of reaction between Tamm Horsfall protein and myoglobin.The casts are usually pigmented.
Urine electrolytes - In rhabdomyolysis you can calculate the Fractionl excretion of Sodium, and this will give an idea about the likely mechanism of AKI. Both pre renal and ATN can contribute to AKI in rhabdomyolysis.
Hope you all have fun with spinning the urine next time!