Urine flow rate is 10 ml/min, plasma inulin is 2 mg/ ml and urine inulin is 25 mg/ml. Which of the following statement is true ?
**Core Concept**
Inulin clearance is used as a measure of glomerular filtration rate (GFR), which is the rate at which the kidneys filter the blood to produce urine. Inulin is a polysaccharide that is neither reabsorbed nor secreted by the renal tubules, making it an ideal substance for measuring GFR.
**Why the Correct Answer is Right**
Inulin clearance is directly proportional to GFR because inulin is freely filtered at the glomerulus and neither reabsorbed nor secreted by the renal tubules. As a result, the amount of inulin excreted in the urine (urine inulin) is directly proportional to the amount of inulin filtered by the glomeruli (GFR). The given data can be used to calculate inulin clearance using the formula: Inulin clearance = (Urine inulin x Urine flow rate) / Plasma inulin. Substituting the given values, we get Inulin clearance = (25 mg/ml x 10 ml/min) / 2 mg/ml = 125 ml/min, which is equal to GFR.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is actually the correct answer, and we've already explained why it's correct. However, we'll reiterate the explanation to ensure clarity.
**Option B:** This option is incorrect because inulin clearance is not greater than GFR. Inulin clearance is a direct measure of GFR, and the two values should be equal if inulin is neither reabsorbed nor secreted by the renal tubules.
**Option C:** This option is a repetition of Option B and is therefore incorrect for the same reason.
**Option D:** This option is incorrect because GFR can indeed be calculated using the given data. By using the inulin clearance formula, we can calculate GFR as equal to inulin clearance.
**Clinical Pearl / High-Yield Fact**
Inulin clearance is a reliable measure of GFR because inulin is neither reabsorbed nor secreted by the renal tubules, making it an ideal substance for measuring GFR. This fact can be remembered using the mnemonic "INULIN IS IDEAL" to represent the key characteristics of inulin.
**✓ Correct Answer: A. Inulin clearance = GFR**