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HelpTest Code 2425D 25-Hydroxyvitamin D:24,25-Dihydroxyvitamin D Ratio, Serum
Reporting Name
25HDN:24,25 Dihydroxy VitD Ratio, SPerforming Laboratory
Mayo Clinic Laboratories in Rochester
Useful For
As a screening test for inactivating CYP24A1 variants in patients with symptoms, signs, or biochemical findings of parathyroid hormone-independent hypercalcemia or hypercalciuria
Method Name
Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS)
Portions of this test are covered by patents held by Quest Diagnostics
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
Collection Instructions: Within 2 hours of collection, centrifuge and aliquot serum into a plastic vial.
Specimen Type
SerumSpecimen Minimum Volume
1.1 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Serum | Refrigerated (preferred) | 14 days | |
| Frozen | 30 days | ||
| Ambient | 7 days |
Reject Due To
| Gross hemolysis | OK |
| Gross lipemia | Reject |
| Gross icterus | OK |
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: Normal; also be observed in heterozygous carriers of CYP24A1 variants
25-80: Seen in patients with low vitamin D or heterozygous CYP24A1 variants
>80: Indicate probable biallelic CYP24A1 variant or deletion
Interpretation
Results should be interpreted in the context of other biochemical findings including serum calcium, parathyroid hormone (PTH), and 1,25 dihydroxyvitamin D (DHVD) concentrations. If 25-hydroxyvitamin D (25HDN) result is less than 20 ng/mL, the ratio of 25HDN to 24,25-dihydroxyvitamin D (24,25D) will be falsely elevated since there is no inactivation of 25HDN to 24,25D.
24,25-Dihydroxyvitamin D formation by CYP24A1 is dependent on CYP24A1 activity and the concentrations of its substrate, 25HDN. The ratio of 25HDN to 24,25D, therefore, allows the most reliable estimation of CYP24A1 activity.
Ratios of 25HDN to 24,25D less than 25 may be interpreted as normal, although ratios less than 25 may also be observed in heterozygous carriers of CYP24A1 variants.
Ratios of 25HDN to 24,25D between the 25 and 80 range may be seen in patients with low vitamin D or having heterozygous CYP24A1 variants. Confirmation with molecular testing is recommended.
Confirmation with molecular testing is also recommended for ratios of 25HDN to 24,25D greater than 80, as this may indicate a probable biallelic CYP24A1 variants or deletion.
Day(s) Performed
Tuesday
Report Available
2 to 8 daysTest 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
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| 2425D | 25HDN:24,25 Dihydroxy VitD Ratio, S | 94674-9 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 2897 | 25-Hydroxy D2 | 49054-0 |
| 63416 | 25HDN:24,25 Dihydroxy VitD Ratio, S | 94673-1 |
| 2898 | 25-Hydroxy D3 | 1989-3 |
| 83670 | 25-Hydroxy D Total | 62292-8 |
| 90601 | 24,25-Dihydroxy VitD Total | 94672-3 |
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 |