Understanding Vitamin D Measurement Units
Laboratory results for 25-hydroxy Vitamin D [25(OH)D] are typically reported in either nanograms per milliliter (ng/mL) or nanomoles per liter (nmol/L). Depending on where you live or which lab you use, the units may vary, making it difficult to interpret your results against clinical guidelines.
The Conversion Factor for Vitamin D
Unlike other substances where the molecular weight must be manually entered, 25-hydroxy Vitamin D has a specific molecular weight that leads to a fixed conversion factor of 2.5.
- To convert ng/mL to nmol/L: Multiply by 2.5.
- To convert nmol/L to ng/mL: Divide by 2.5.
Clinical Interpretation of Levels
While reference ranges can vary by laboratory, general clinical guidelines often categorize Vitamin D status as follows:
| Status | ng/mL | nmol/L |
|---|---|---|
| Deficiency | < 20 | < 50 |
| Insufficiency | 20 - 29 | 50 - 74 |
| Sufficiency | 30 - 100 | 75 - 250 |
| Toxicity | > 100 | > 250 |
Formula:
Formula: ng/mL × 2.5 = nmol/L