Which laboratory test is primarily used to assess kidney function?

The primary laboratory test used to assess kidney function is the serum creatinine level. This test measures the amount of creatinine in the blood, which is a waste product formed from muscle metabolism. The kidneys are responsible for filtering creatinine out of the blood and excreting it in urine. Therefore, elevated levels of serum creatinine can indicate decreased kidney function or kidney damage, making it a crucial marker for assessing renal health.

In contrast, a complete blood count is a test that evaluates overall health and detects various disorders like anemia or infection, but it does not specifically provide information about kidney function. Liver function tests assess the health of the liver, measuring enzymes and substances that reflect liver performance and damage. Blood glucose levels are important for evaluating conditions like diabetes but do not relate to kidney function assessment. Thus, the serum creatinine level is distinctive for gauging how well the kidneys are working.