Blood urea nitrogen and serum creatinine: Physiology and interpretations

Any elevations in levels of blood urea nitrogen and/or serum creatinine do not necessarily indicate structural renal disease. Conversely, blood urea nitrogen or serum creatinine values, which appear to be within the range of normal, do not by themselves rule out significant reduction in glomerular filtration rate. Any interpretation of the blood levels of these two substances must be done with the awareness that a variety of extrarenal factors can affect them. The blood urea nitrogen to serum creatinine ratio can be a valuable tool in the determination of renal functional and structural integrity.