25-Hydroxyvitamin D:24,25-Dihydroxyvitamin D Ratio, Serum
Use
This test is useful for screening for inactivating CYP24A1 variants in patients with symptoms, signs, or biochemical findings of parathyroid hormone-independent hypercalcemia or hypercalciuria. The ratio of 25-hydroxyvitamin D (25HDN) to 24,25-dihydroxyvitamin D (24,25D), measured in serum, can indicate the activity of CYP24A1 and help diagnose disorders such as CYP24A1 deficiency or vitamin D intoxication. Low ratio values might be normal or indicate heterozygous CYP24A1 variants, while high ratios suggest likely CYP24A1 biallelic mutations or deletions.
Special Instructions
The test should be performed using the same methodology for both analytes to maintain consistent ratio measurements. Measurement consistency is critical, given the substrate dependence of the 25HDN to 24,25D ratio. Specimen should be centrifuged and aliquoted within 2 hours of collection.
Limitations
The test may yield false low ratios due to separate measurements of the components. Additionally, it may lead to delayed diagnosis if misinterpreted. The accuracy of the ratio is dependent on the precise measurement of both vitamin D metabolites using the same blood sample and technique. False-high ratios could prompt unnecessary genetic testing.
New York Approved
Methodology
Mass Spectrometry (LC-MS/MS)
Biomarkers
LOINC Codes
- 94674-9
- 49054-0
- 1989-3
- 62292-8
- 94672-3
- 94673-1
Result Turnaround Time
2-15 days
Related Documents
For more information, please review the documents below
Specimen
Serum
Volume
1.7 mL
Minimum Volume
1.1 mL
Container
Plastic vial
Collection Instructions
Within 2 hours of collection, centrifuge and aliquot serum into a plastic vial.
Causes for Rejection
Gross lipemia
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 7 days |
| Refrigerated | 14 days |
| Frozen | 30 days |