How should vitamin D deficiency be diagnosed and managed in a healthy adult?

Testing for Vitamin D Deficiency in Healthy Adults

The USPSTF does not recommend routine screening for vitamin D deficiency in asymptomatic, healthy adults without risk factors. 1, 2

When to Test

Do NOT routinely screen:

• Asymptomatic, healthy adults should not undergo population-wide screening as there is insufficient evidence that screening and treating vitamin D deficiency in this population improves mortality, falls, fractures, cancer, diabetes, or physical functioning 1
• The lack of benefit applies specifically to community-dwelling adults without signs or symptoms of deficiency 1

DO consider testing in:

• Patients with symptoms of deficiency: symmetric low back pain, proximal muscle weakness, muscle aches, or throbbing bone pain with pressure over sternum or tibia 3
• Patients being evaluated for osteoporosis management or fall prevention 1
• Patients with specific risk factors (though population screening remains not recommended): obesity (BMI ≥30), very low sun exposure, dark skin, latitude ≥48°N, winter/late winter season 4
• Patients with sarcoidosis before considering vitamin D replacement (requires both 25(OH)D and 1,25(OH)₂D testing due to risk of hypercalcemia) 2

Which Test to Order

Order serum 25-hydroxyvitamin D [25(OH)D] - this is the correct biomarker for assessing vitamin D status 2, 5

Critical testing considerations:

• Do NOT order 1,25-dihydroxyvitamin D [1,25(OH)₂D] for routine vitamin D status assessment - it provides no information about vitamin D stores and is often normal or elevated in deficiency due to secondary hyperparathyroidism 5
• Be aware that significant variability exists between assay methods (4-32% variation in classification of deficiency depending on which assay is used), though standardization efforts are ongoing 1, 6
• Inflammation can falsely lower plasma vitamin D levels, complicating interpretation 7

Interpreting Results

Deficiency thresholds:

• Deficiency: <20 ng/mL (<50 nmol/L) 7, 3, 5
• Insufficiency: 20-30 ng/mL (50-75 nmol/L) 3, 5
• Severe deficiency: <10-12 ng/mL (<25-30 nmol/L) - significantly increases risk for osteomalacia and rickets 7
• Target level after treatment: ≥30 ng/mL (≥75 nmol/L) 7, 5

Treatment When Deficiency is Found

For documented deficiency, prescribe ergocalciferol (vitamin D2) 50,000 IU once weekly for 8 weeks 7, 3

Treatment protocol:

• This loading dose is necessary because standard daily doses take many weeks to normalize levels 7
• After 8-week loading phase, transition to maintenance therapy of 1,500-2,000 IU daily (or 800-1,000 IU daily per some sources) 7, 3
• Recheck 25(OH)D level after 3-6 months to ensure adequate response 7
• Adjust dose if levels remain insufficient 7

Safety considerations:

• Vitamin D toxicity is rare at recommended doses and typically only occurs at levels >200 ng/mL 7
• Avoid calcium co-supplementation if kidney stone risk is a concern 7

Key Pitfalls to Avoid

• Do not screen asymptomatic healthy adults - this wastes resources without proven benefit to mortality or quality of life 1
• Do not order 1,25(OH)₂D for routine assessment - wrong test for vitamin D status 2, 5
• Do not use single large bolus doses (300,000-500,000 IU) - these should be avoided 8
• Do not assume all assays are equivalent - significant inter-laboratory variability exists 1, 6