NaF is used in which color cap vacutainer?
**Core Concept**
The question tests knowledge of **phlebotomy** and **vacutainer tube** colors, specifically the use of **sodium fluoride (NaF)** in blood collection. Sodium fluoride is used as a **glycolytic inhibitor** to prevent glucose metabolism in blood samples.
**Why the Correct Answer is Right**
NaF is used in **gray cap vacutainers** because it inhibits **enolase**, an enzyme involved in glycolysis, thereby preserving glucose levels in the sample. This is crucial for accurate measurement of **glucose** in clinical settings.
**Why Each Wrong Option is Incorrect**
**Option A:** Wrong because NaF is not typically used in this color vacutainer.
**Option B:** Incorrect as this color is associated with a different additive.
**Option D:** Incorrect because this color corresponds to a different type of blood collection tube.
**Clinical Pearl / High-Yield Fact**
Remember, **gray top tubes** contain NaF and **potassium oxalate**, making them ideal for **glucose** testing.
**Correct Answer:** D. Gray