 BUN-to-creatinine ratio (the ratio of blood urea nitrogen to creatinine) can indicate other problems besides those intrinsic to the kidney; for example, a urea concentration raised out of proportion to the creatinine may indicate a prerenal problem such as volume depletion.Each day, 1% to 2% of muscle creatine is converted to creatinine.The conversion is nonenzymatic and irreversible.