A 40-year old alcoholic male is being treated for TB, but he has not been regular with his medications. He complains of increasing weakness and fatigue. He appears to have lost weight and his BP is 80/50. There is increased pigmentation over the elbows. Cardiac exam is normal. The next step in evaluation should be

**Core Concept**
The patient's presentation suggests adrenal insufficiency, likely due to **tuberculosis** affecting the adrenal glands, given the context of TB treatment and symptoms such as weakness, fatigue, weight loss, hypotension, and increased pigmentation.

**Why the Correct Answer is Right**
The correct approach involves investigating the cause of suspected adrenal insufficiency, particularly in a patient with a history of TB, which can cause **adrenal gland destruction** leading to **Addison's disease**. The increased pigmentation is a classic sign of **ACTH** (adrenocorticotropic hormone) stimulation due to lack of cortisol feedback.

**Why Each Wrong Option is Incorrect**
**Option A:** Would be incorrect as it doesn't directly relate to the diagnosis of adrenal insufficiency.
**Option B:** Might be considered in some cases of hypotension but doesn't address the underlying issue of suspected adrenal insufficiency.
**Option C:** Could be relevant in broader assessments but is not the next best step given the specific clinical presentation.
**Option D:** Is the correct choice as it involves assessing the adrenal function directly.

**Clinical Pearl / High-Yield Fact**
In patients with suspected adrenal insufficiency, particularly those with a history of TB, an **ACTH stimulation test** or **cosyntropin test** is crucial for diagnosis.

**Correct Answer:** D. Cosyntropin test

✓ Correct Answer: C. Early morning serum coisol