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HelpTest Code 2425D 25-Hydroxyvitamin D:24,25-Dihydroxyvitamin D Ratio, Serum
Ordering Guidance
The preferred initial test for assessing vitamin D status and most accurately reflects the body's vitamin D stores is the 25-hydroxyvitamin D test; order 25HDN / 25-Hydroxyvitamin D2 and D3, Serum.
In the presence of kidney disease or hypercalcemia, testing of 1,25-dihydroxy vitamin D may be needed to adequately assess vitamin D status; order DHVD / 1,25-Dihydroxyvitamin D, Serum.
Specimen Required
Supplies: Sarstedt Aliquot Tube, 5 mL (T914)
Collection Container/Tube: Red top
Submission Container/Tube: Plastic vial
Specimen Volume: 1.7 mL Serum
Collection Instructions: Within 2 hours of collection, centrifuge and aliquot serum into a plastic vial.
Useful For
Screening for CYP24A1 deficiency
Evaluation of parathyroid hormone-independent hypercalcemia
Evaluation of recurrent nephrolithiasis or nephrocalcinosis associated with suspected vitamin D-mediated disease
Selection of patients for confirmatory molecular testing
Profile Information
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| 2425R | 24,25 Dihydroxy Vitamin D | No | Yes |
| 25HDN | 25-Hydroxyvitamin D2 and D3, S | Yes | Yes |
Method Name
Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS)
Portions of this test are covered by patents held by Quest Diagnostics
Reporting Name
25HDN:24,25 Dihydroxy VitD Ratio, SSpecimen Type
SerumSpecimen Minimum Volume
Serum: 1.1 mL
Specimen Stability Information
| Specimen Type | Temperature | Time |
|---|---|---|
| Serum | Refrigerated (preferred) | 14 days |
| Frozen | 30 days | |
| Ambient | 7 days |
Reject Due To
| Gross hemolysis | OK |
| Gross lipemia | Reject |
| Gross icterus | OK |
Clinical Information
The ratio of 25-hydroxyvitamin D (25HDN) to 24,25-dihydroxyvitamin D (24,25D) provides an estimate of CYP24A1 enzymatic activity. CYP24A1 is responsible for inactivation of both 25HDN and 1,25-dihydroxyvitamin D (DHVD). Loss of function variants in the CYP24A1 gene impair vitamin D catabolism, resulting in a phenotype characterized by suppressed serum parathyroid hormone (PTH), increased serum DHVD concentrations, hypercalcemia, and hypercalciuria that may lead to nephrolithiasis. Because 24,25D production depends on substrate availability (25HDN concentration) and CYP24A1 activity, interpretation of the ratio requires simultaneous measurement of both analytes in the same specimen. The ratio is most useful in patients with suspected CYP24A1 deficiency and should be interpreted in conjunction with serum calcium, PTH, 25HDN, DHVD test results and clinical presentation.
Reference Values
Interpretative commentary provided based on 25-hydroxyvitamin D (25HDN) to 24,25-dihydroxyvitamin D (24,25D) ratio result.
25HDN to 24,25D Ratio
<25: Consistent with normal CYP24A1 activity, although overlap with heterozygous carriers has been reported.
25-80: May be observed in vitamin D deficiency or heterozygous CYP24A1 variants. Correlation with clinical findings is recommended. Molecular testing may be appropriate when clinical suspicion is high.
>80: Strongly suggests markedly reduced CYP24A1 activity. Confirmatory molecular testing is recommended.
Day(s) Performed
Wednesday
Report Available
2 to 15 daysPerforming Laboratory
Mayo Clinic Laboratories in Rochester
Test Classification
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.CPT Code Information
82306
82542