BUN Creatinine Ratio Test in California

What this test measures

Blood urea nitrogen, or BUN, is a waste product formed when the liver breaks down protein, and it is cleared by the kidneys. Creatinine is a waste product from normal muscle activity that is also filtered by the kidneys. Comparing the two gives a ratio that adds context beyond either value alone, because they can change at different rates when kidney function, hydration, or protein intake shifts.

The test uses a standard blood sample drawn from a vein. Results are reported as a calculated ratio, typically alongside the individual BUN and creatinine concentrations. Because the ratio depends on both numbers, laboratories and clinicians review the underlying values rather than the ratio in isolation. Conditions such as dehydration, a high-protein diet, gastrointestinal bleeding, or liver disease can influence the balance.

Clinicians may order this ratio when a routine metabolic panel shows an unexpected BUN or creatinine level, or when they are evaluating kidney function, hydration, or a suspected gastrointestinal bleed. It is not a diagnosis on its own, and a qualified healthcare provider should interpret it in the context of symptoms, medications, and other tests.