Vitamin D, 25-OH (D2 + D3, LC/MS/MS)
What This Test Measures
Mass spectrometry method separating D2 (ergocalciferol) and D3 (cholecalciferol); most accurate method.
Preparation
TIMING: Stop vitamin D supplements for 24–48 hours before the draw. After starting a loading dose, wait 2–3 months before retesting. The functional medicine community targets 50–80 ng/mL, significantly above the standard 30 ng/mL floor. LC/MS/MS is the gold standard methodology — more accurate than immunoassay, especially for D2 vs D3 breakdown. For Hashimoto's or chronic illness, practitioners target the higher end. Note: for hyperparathyroidism or kidney disease, discuss targets with your provider.
Reflects common practices in thyroid, BHRT, and functional medicine communities. This may differ from standard clinical guidelines. Not medical advice — always discuss with your provider.
General guidelines only. Requirements vary by lab and individual. Confirm with your provider before adjusting any medications.
Turnaround Time
Varies by lab
Clinical Notes
Gold standard; distinguishes supplemental D2 from endogenous/supplemental D3
ICD-10 Codes
Common diagnosis codes associated with this test. Codes are assigned by your provider.
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Lab Codes
Proprietary codes used by each lab for this test.
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For informational purposes only
This page is for educational and research purposes only and does not constitute medical advice, diagnosis, or treatment recommendations. ICD-10 and CPT codes are assigned by your healthcare provider. Always consult a qualified healthcare provider before ordering any lab test or making decisions about your health.