Okay, let's tackle this question. The user is asking about the anticoagulant used in a PHC (Primary Health Center) for blood glucose estimation. First, I need to recall the common anticoagulants used in blood collection. The main ones are EDTA, heparin, citrate, and others like sodium fluoride.

Blood glucose testing requires that the sample doesn't clot. So the anticoagulant must prevent clotting without interfering with the glucose measurement. EDTA is a common anticoagulant, but it can interfere with some glucose tests. Heparin is another option, but I remember sodium fluoride is often used because it inhibits glycolysis, preserving glucose levels. Wait, sodium fluoride actually acts as a preservative by inhibiting the glycolytic enzymes in the blood, which prevents the breakdown of glucose by red blood cells. That makes it suitable for preserving glucose levels over time.

So the correct answer should be sodium fluoride. Let me check the options again. The options aren't listed, but the user mentioned the correct answer is one of them. The key here is that sodium fluoride is the right anticoagulant for glucose testing. Other anticoagulants like EDTA or heparin might not preserve glucose as effectively because they don't inhibit glycolysis.

Wait, sodium citrate is used for coagulation tests, not glucose. So options like EDTA or citrate would be incorrect. Heparin is an anticoagulant but doesn't prevent glycolysis. So sodium fluoride is the correct choice. The clinical pearl here is that sodium fluoride is specifically used to prevent glycolysis, ensuring accurate glucose readings. Students often mix up anticoagulants for different tests, so remembering that sodium fluoride is paired with glucose testing is key.

**Core Concept**
The question tests knowledge of anticoagulants used in blood collection for glucose estimation. Sodium fluoride is the key preservative for this test, as it inhibits glycolysis and prevents glucose degradation in blood samples.

**Why the Correct Answer is Right**
Sodium fluoride inhibits glycolytic enzymes (e.g., enolase) in blood, preventing glucose metabolism by erythrocytes. This preserves glucose levels until analysis. It is typically combined with an anticoagulant like EDTA or citrate in blood collection tubes to ensure both anticoagulation and glucose stabilization.

**Why Each Wrong Option is Incorrect**
**Option A:** EDTA alone prevents clotting but does not inhibit glycolysis, leading to falsely low glucose results.
**Option B:** Heparin is an anticoagulant but does not preserve glucose; glycolysis continues, causing rapid glucose depletion.
**Option C:** Sodium citrate is used for coagulation tests (e.g., PT, aPTT) and not for glucose estimation.

**Clinical Pearl / High-Yield Fact**
Never use plain heparin or EDTA for glucose testing. Always use sodium fluoride-containing tubes to avoid glycolysis. Remember: **Fluoride = Glucose preservation** (mnemonic: "Fluoride stops glucose from 'flying away'").

**Correct Answer: D. Sodium fluoride**

✓ Correct Answer: D. Potassium oxalate + sodium fluoride