Question

You are performing an insulin clearance test on a patient in order to determine their GFR. Insulin is being infused such that blood plasma concentration is 0.5 mg/mL. The patient produces urine that has an insulin concentration of 40 mg/mL at a rate of 1.5 mL/min. What is this patient's GFR in mL/min?

Answer 1

The glomerular filtration rate (GFR) for the patient, calculated using the insulin clearance test, is 120 mL/min. This value is derived by applying the formula using the urine and plasma concentrations of insulin and the urine flow rate.

Step-by-step explanation:

To calculate the glomerular filtration rate (GFR) using the insulin clearance test, apply the formula GFR = (Urine Concentration * Urine Flow Rate) / Plasma Concentration. Here, Insulin replaces Inulin in the test, but the principle remains the same because neither is significantly reabsorbed or secreted by the kidneys. Thus, the rate at which a substance appears in the urine reflects its rate of filtration.

In this scenario:

• Urine Insulin Concentration (U) = 40 mg/mL
• Urine Flow Rate (V) = 1.5 mL/min
• Plasma Insulin Concentration (P) = 0.5 mg/mL

GFR = (U * V) / P = (40 mg/mL * 1.5 mL/min) / 0.5 mg/mL

GFR = 60 / 0.5 = 120 mL/min

The patient's GFR is 120 mL/min, which is within the normal range for healthy adults. This indicates a typical functioning of the kidneys in terms of filtration capacity.

Using the insulin clearance test values provided and following the respective formula for the calculation of GFR, the patient's glomerular filtration rate is determined to be 120 mL/min. This is an important measure of kidney function and indicates good renal health in the context of this test.