A 52-year-old man complains of impotence. On physical examination, he has an elevated jugular venous pressure, S3 gallop, and hepatomegaly. He also appears tanned, with pigmentation along skin folds. He has joint pain and bony overgrowth primarily affecting the second and third metacarpophalangeal joints bilaterally. The plasma glucose is 250 mg/dL, and liver enzymes are elevated. Which of the following studies will help establish the diagnosis?

**Core Concept**
The patient's symptoms suggest a metabolic disorder with associated endocrine, hepatic, and musculoskeletal manifestations. The clinical presentation is consistent with acromegaly, a disorder caused by excess growth hormone (GH) production, often due to a pituitary adenoma.

**Why the Correct Answer is Right**
The diagnosis of acromegaly can be confirmed by measuring insulin-like growth factor-1 (IGF-1) levels, which reflect the integrated effect of GH on target tissues. Elevated IGF-1 levels indicate excess GH production, leading to the characteristic clinical features of acromegaly. In this patient, the elevated glucose and liver enzymes also suggest insulin resistance, a common finding in acromegaly.

**Why Each Wrong Option is Incorrect**
* **Option A:** A fasting glucose level would not be diagnostic for acromegaly, as patients may have normal glucose levels despite insulin resistance.
* **Option B:** A thyroid-stimulating hormone (TSH) level would not help establish the diagnosis of acromegaly, as the condition is caused by excess GH production, not thyroid dysfunction.
* **Option D:** A serum creatinine level would not be relevant to the diagnosis of acromegaly, as the condition does not primarily affect kidney function.

**Clinical Pearl / High-Yield Fact**
Acromegaly is often associated with an increased risk of developing colon cancer, insulin-dependent diabetes mellitus, and sleep apnea. Regular screening for these complications is essential in patients with acromegaly.

**Correct Answer:** C.

✓ Correct Answer: B. Determination of iron saturation