Blood Spot Vitamin D (25-OH) by LC-MS Test
The blood spot vitamin D test measures total 25-hydroxyvitamin D by LC-MS from a capillary dried blood spot collected by finger-stick, enabling vitamin D status assessment without a venous draw. It reports a single total value calibrated to the dried-blood-spot matrix, suited to remote and serial monitoring, and is not numerically interchangeable with venous serum assays.
1
Biomarkers
Dried blood spot
Sample
5–7 business days
Turnaround
No
Fasting
What is the Blood Spot Vitamin D test?
The Blood Spot Vitamin D (25-OH) by LC-MS Test measures total 25-hydroxyvitamin D from a capillary dried blood spot collected by finger-stick, offering vitamin D status assessment without attendance for a venous draw. It reports a single total 25-OH-D by liquid chromatography–mass spectrometry, calibrated by the laboratory to the dried-blood-spot matrix. Its role is defined by the specimen rather than the analyte: the clinical question is the same as any 25-OH-D — is the patient replete — but the dried-blood-spot format makes it suited to remote consultations, serial home monitoring of a repletion programme, paediatric or needle-averse patients, and settings where phlebotomy access is a barrier. Where the vitamer source must be distinguished (prescription D2 versus D3), a fractionated venous assay is the more appropriate choice; where convenient serial total-status monitoring is the goal, the dried blood spot is well matched.
What does the Blood Spot Vitamin D test measure?
25-Hydroxyvitamin D is the major circulating vitamin D metabolite and the accepted index of vitamin D stores, with a half-life of roughly two to three weeks. In a dried-blood-spot specimen it is measured from capillary whole blood dried onto a filter card, so the result reflects a whole-blood matrix rather than separated serum; laboratories apply method-specific calibration to report a value aligned to circulating 25-OH-D. The measurement here is total 25-OH-D by LC-MS and is not reported as separate D2 and D3 fractions.
A capillary dried-blood-spot total 25-OH-D supports status assessment and longitudinal monitoring without a venous draw, which suits remote, serial, or patient-collected workflows common in functional and preventive practice. Because the specimen matrix and calibration differ from venous serum, results are best trended against the same method rather than cross-compared with a serum assay from another laboratory.
Why is the Blood Spot Vitamin D test ordered?
- Remote or telehealth practice where a patient-collected finger-stick card removes the need to attend a phlebotomy site
- Serial monitoring of a vitamin D repletion programme where trending on a single consistent method matters more than cross-lab comparison
- Needle-averse patients, and paediatric or geriatric patients in whom venous collection is difficult
- Preventive and functional-medicine reviews that bundle dried-blood-spot vitamin D with other blood-spot analytes from one collection
- Patients in locations with limited access to a draw site, where a mailed collection kit is the practical option
- Longitudinal wellness monitoring where the practitioner wants a low-burden, repeatable total 25-OH-D
Sample collection and turnaround
Sample type
Dried blood spot
Fasting required
No
Collection method
Finger prick
Turnaround
5–7 business days
Collection notes
Self-collected capillary dried blood spot using the ZRT Laboratory kit: finger-stick lancet onto the supplied filter card, fully air-dried, then returned to the laboratory per kit instructions. Fill the required spots completely without milking the finger. Record supplementation dose and timing.
Specimen requirements
Adequately filled, fully dried blood-spot card per ZRT specification. Return promptly; avoid heat and humidity in transit.
What can affect Blood Spot Vitamin D results?
Insufficient blood volume, incompletely filled or layered spots, or squeezing (milking) the finger can bias dried-blood-spot results; adherence to the kit instructions is essential to a valid specimen.
The volume of analyte in a fixed-area blood spot depends on haematocrit, which can influence dried-blood-spot quantitation at the extremes and is a recognised matrix consideration.
Although 25-OH-D is relatively stable on dried cards, excess humidity, heat, or prolonged transit can degrade specimen quality; cards should be dried fully and returned promptly per kit instructions.
A large recent oral dose raises measured 25-OH-D; record the dose and timing for correct serial interpretation.
Adipose sequestration lowers circulating 25-OH-D for a given intake, so higher or more sustained dosing may be needed to reach target.
Dried-blood-spot values are calibrated to a whole-blood matrix and are not numerically interchangeable with venous serum assays, so a result should not be compared directly with a serum 25-OH-D from another laboratory.
What do Blood Spot Vitamin D results mean?
Elevated
A high total 25-OH-D reflects substantial sun exposure or supplementation; markedly elevated values warrant review of dosing and, where clinically indicated, assessment for hypercalcaemia. Confirm an unexpectedly high dried-blood-spot result before major clinical action.
Normal
A total 25-OH-D within the laboratory's dried-blood-spot target indicates adequate status for that method. Interpret serial results against the same dried-blood-spot assay rather than switching matrices mid-monitoring.
Reduced
A low total 25-OH-D indicates deficiency from inadequate cutaneous synthesis or intake, often compounded by malabsorption or obesity. A collection-quality issue should be excluded before attributing a very low result solely to deficiency.
Note: This is a total 25-OH-D on a capillary dried-blood-spot matrix — it does not fractionate D2 and D3 and is not interchangeable with venous serum assays. Collection quality is a material determinant of validity. 1,25-dihydroxyvitamin D is not a status marker and is not substituted here.
Frequently asked questions
Both measure 25-hydroxyvitamin D, but the dried blood spot uses capillary whole blood on a filter card with method-specific calibration, while a serum test uses separated venous serum. Results are not numerically interchangeable and should be trended within the same method.
How to access the Blood Spot Vitamin D test
The Blood Spot Vitamin D reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.
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Published: October 7, 2026
Last reviewed: October 7, 2026
- Holick MF, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. (2011)
- Sempos CT, et al. Vitamin D assays and the definition of hypovitaminosis D: controversies in vitamin D. Br J Clin Pharmacol. (2018)
- Larkin EK, et al. Dried blood spot measurement of 25-hydroxyvitamin D: validation against serum. (verify). (2017)
- Ross AC, et al. Dietary reference intakes for calcium and vitamin D. J Clin Endocrinol Metab. (2011)
This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.
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The blood spot vitamin D test measures total 25-hydroxyvitamin D by LC-MS from a capillary dried blood spot collected by finger-stick, enabling vitamin D status assessment without a venous draw. It reports a single total value calibrated to the dried-blood-spot matrix, suited to remote and serial monitoring, and is not numerically interchangeable with venous serum assays.