Categories of renal failure. Once the presence of renal failure is ascertained by elevated blood urea nitrogen (BUN) or serum creati-nine value, the clinician must decide whether it is acute or chronic. When previous values are available for review, this judgment is made relatively easily. In the absence of such values, the factors depicted here may be helpful. Hemoglobin potentially undergoes nonenzymatic carbamylation of its terminal valine . Thus, similar to the hemoglobin A1C value as an index of blood sugar control, the level of carbamylated hemoglobin is an indicator of the degree and duration of elevated BUN, but, this test is not yet widely available. The presence of small kidneys strongly suggests that renal failure is at least in part chronic. From a practical standpoint, because even chronic renal failure often is partially reversible, the clinician should assume and evaluate for the presence of acute reversible factors in all cases of acute renal failure.
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