What laboratory finding would suggest renal failure in a patient with hyperkalemia?

In a patient presenting with hyperkalemia, the laboratory finding that would strongly suggest renal failure is elevated creatinine levels. This is due to the crucial role the kidneys play in filtering waste products from the blood, including creatinine, which is a byproduct of muscle metabolism. When renal function declines, the kidneys are less able to clear creatinine effectively, leading to its accumulation in the bloodstream.

Hyperkalemia itself is often a direct consequence of renal failure since the kidneys also regulate potassium balance. When they fail to excrete potassium adequately, elevated levels can occur. Therefore, the presence of elevated creatinine, in conjunction with hyperkalemia, indicates compromised renal function and supports the diagnosis of renal failure.

Other laboratory values, such as low bicarbonate, high glucose, or low calcium, may provide additional clinical information but are not direct indicators of renal failure. Low bicarbonate may indicate metabolic acidosis, which can occur with or without renal failure; high glucose can suggest diabetes or stress response; low calcium might indicate various conditions but does not directly reflect renal function as elevated creatinine does. Thus, elevated creatinine is the most relevant laboratory finding in this context.