Which thresholds define 25-hydroxyvitamin D deficiency, insufficiency, and sufficiency?

• A. Deficiency <20 ng/mL; insufficiency 20–29 ng/mL; sufficiency ≥30 ng/mL.
• B. Deficiency <30 ng/mL; insufficiency 20–29 ng/mL; sufficiency ≥40 ng/mL.
• C. Deficiency <10 ng/mL; insufficiency 10–19 ng/mL; sufficiency ≥20 ng/mL.
• D. Deficiency <15 ng/mL; insufficiency 15–24 ng/mL; sufficiency ≥25 ng/mL.

Answer: (A)

The main idea is how circulating 25-hydroxyvitamin D levels categorize vitamin D status to reflect bone health risk. This classification uses a threshold of less than 20 ng/mL for deficiency, 20–29 ng/mL for insufficiency, and 30 ng/mL or higher for sufficiency. These cutoffs are chosen because 25(OH)D is the best overall indicator of vitamin D stores from sun exposure and diet, and bone health improves as levels rise toward 30 ng/mL and above. Deficiency below 20 ng/mL is linked with impaired mineralization and risk of rickets or osteomalacia, while 20–29 ng/mL represents insufficient stores that may still affect bone turnover. Levels at or above 30 ng/mL are considered adequate for most individuals. Other proposed thresholds differ by whether they raise the deficiency or sufficiency cutpoints, which can misclassify people relative to bone-health outcomes.