Screening test for vitamin D deficiency is
**Core Concept**
Vitamin D deficiency is a common nutritional disorder affecting bone health, with symptoms ranging from rickets in children to osteomalacia in adults. The diagnosis of vitamin D deficiency involves measuring the levels of 25-hydroxyvitamin D [25(OH)D] in the blood, which is the primary indicator of vitamin D status.
**Why the Correct Answer is Right**
The correct answer is the 25-hydroxyvitamin D (25(OH)D) test, also known as the 25-hydroxyvitamin D assay or 25(OH)D level. This test measures the concentration of 25(OH)D in the blood, which is the major circulating form of vitamin D. The 25(OH)D level is used to diagnose vitamin D deficiency, insufficiency, and sufficiency. The test is a reliable indicator of vitamin D status because it reflects the body's vitamin D stores, which are determined by dietary intake, sun exposure, and skin synthesis.
**Why Each Wrong Option is Incorrect**
**Option A:** Parathyroid hormone (PTH) levels are often elevated in vitamin D deficiency, but measuring PTH is not a primary screening test for vitamin D deficiency.
**Option B:** Serum calcium levels may be low in severe vitamin D deficiency, but measuring serum calcium is not a specific or sensitive test for vitamin D deficiency.
**Option C:** Serum phosphorus levels may be low in vitamin D deficiency, but measuring serum phosphorus is not a primary screening test for vitamin D deficiency.
**Clinical Pearl / High-Yield Fact**
The 25(OH)D level is a useful indicator of vitamin D status, but it is essential to consider the season, sun exposure, and skin pigmentation when interpreting the results. In general, a 25(OH)D level below 20 ng/mL is considered deficient, while a level between 20-30 ng/mL is considered insufficient.
**Correct Answer: 1. 25-hydroxyvitamin D (25(OH)D) test**