Vitamin D (25 Hydroxy)

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General Information

Lab Name
Vitamin D (25 Hydroxy)
Lab Code
VITDG2
Epic Ordering
Vitamin D 25-OH COMMON Deficiency Level
Description

The concentration of 25-hydroxyvitamin D2 and D3 in serum/plasma are determined by heptane liquid-liquid extraction and liquid chromatography-tandem mass spectrometry. The reportable range is 1 - 200 ng/mL with imprecision between 7.7 and 11.5 %CV.

This is the preferred initial test for assessing vitamin D status in patients without renal disease. See Vitamin D Testing Recommendations for an overview of Vitamin D testing.

There is considerable debate over the range of total 25-hydroxy vitamin D concentrations in serum or plasma that is consistent with optimal health. Currently, there are no consensus guidelines for targeting plasma 25-hydroxy vitamin D concentrations and no studies addressing the outcomes of long-term vitamin D supplementation in general populations. Therefore, we have reviewed the available literature and performed population studies here in Seattle to arrive at our interpretive ranges (see Reference Range section below).

References
  • Holick MF. Vitamin D deficiency. N Engl J Med 2007, 357:266-81. 17634462
  • Cauley JA, Lacroix AZ, Wu L, Horwitz M, Danielson ME, Bauer DC, Lee JS, Jackson RD, Robbins JA, Wu C, Stanczyk FZ, LeBoff MS, Wactawski-Wende J, Sarto G, Ockene J, and Cummings SR. Serum 25-hydroxyvitamin D concentrations and risk for hip fractures. Ann Intern Med 2008, 149:242-50. 18711154
  • Jackson RD, LaCroix AZ, Gass M, Wallace RB, Robbins J, Lewis CE, Bassford T, Beresford SA, Black HR, Blanchette P, Bonds DE, Brunner RL, Brzyski RG, Caan B, Cauley JA, Chlebowski RT, Cummings SR, Granek I, Hays J, Heiss G, Hendrix SL, Howard BV, Hsia J, Hubbell FA, Johnson KC, Judd H, Kotchen JM, Kuller LH, Langer RD, Lasser NL, Limacher MC, Ludlam S, Manson JE, Margolis KL, McGowan J, Ockene JK, O'Sullivan MJ, Phillips L, Prentice RL, Sarto GE, Stefanick ML, Van Horn L, Wactawski-Wende J, Whitlock E, Anderson GL, Assaf AR, Barad D, and Women's Health Initiative Investigators.. Calcium plus vitamin D supplementation and the risk of fractures. N Engl J Med 2006, 354:669-83. 16481635
  • Looker AC and Mussolino ME. Serum 25-hydroxyvitamin D and hip fracture risk in older U.S. white adults. J Bone Miner Res 2008, 23:143-50. 17907920
  • Saenger AK, Laha TJ, Bremner DE, and Sadrzadeh SM. Quantification of serum 25-hydroxyvitamin D(2) and D(3) using HPLC-tandem mass spectrometry and examination of reference intervals for diagnosis of vitamin D deficiency. Am J Clin Pathol 2006, 125:914-20. 16690491
  • Vieth R. Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety. Am J Clin Nutr 1999, 69:842-56. 10232622
Synonyms
25-Hydroxycholecalciferol, VITDG
Components

Interpretation

Method

Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Reference Range
See individual components
Ref. Range Notes

Reference ranges for Total 25-Hydroxy Vitamin D

Concentration range (ng/mL) Interpretation
less than 8 severe deficiency
8 - 20 deficiency
20.1 - 50 normal
50.1 - 80 high indicates supplementation
greater than 80 possible toxicity

Studies addressing a recommended lower limit for optimal 25-hydroxy vitamin D concentration have largely relied on surrogate markers such as stabilization of parathyroid hormone concentrations or excretion of calcium in urine. These have determined that 30-32 ng/mL of 25-hydroxy vitamin D is sufficient to prevent calcium wasting and inhibit compensatory mechanisms [reviewed in Holick, 2007]. However, other studies have demonstrated that there is actually a higher rate of hip fracture in populations with 25-hydroxy vitamin D concentrations above 28-32 ng/mL (Looker, 2008 and Cauley, 2008). From the bulk of the available literature it appears that 25-hydroxy vitamin D levels above 20 ng/mL are important for good bone health, but there is insufficient evidence to supplement the diet of all patients with plasma or serum 25-hydroxy vitamin D concentrations between 20 and 30 ng/mL.

Now let us turn to the upper limit of the recommended range. In a population of laboratory personnel in Seattle not taking supplements, the highest concentration of 25-hydroxy vitamin D measured was 43.9 ng/mL (N=40) (Saenger, 2006). From the literature, the highest concentration of 25-hydroxy vitamin D in a person not taking supplements was 64 ng/mL, which was detected in a lifeguard at 30° latitude in the summer months (Vieth, 1999). From this information, it appears that people living in the Pacific Northwest are quite unlikely to have concentrations exceeding 50 ng/mL unless they are taking supplemental vitamin D. In addition to these data, the literature reports the lowest serum concentration of 25-hydroxy vitamin D associated with what appeared to be hypervitaminosis was 88.4 ng/mL (Vieth, 1999). We have decided to be conservative and use >80 ng/mL as our level of possible toxicity. It should be noted that there have been no long-term studies showing the safety and efficacy of vitamin D supplementation to levels above 30 ng/mL in the general population. In fact, the best study so far demonstrated that vitamin D supplementation in patients at higher risk for hip fractures had more kidney stones and no improvement in the rate of hip fracture (Jackson, 2006). Therefore, we include two upper limits in our interpretive comments, one suggestive of supplementation in the Pacific Northwest population (>50 ng/mL) and one that is consistent with possible toxicity (>80 ng/mL).

Guidelines

Ordering & Collection

Specimen Type
Blood
Collection
  • Preferred: 4 mL blood in Gold SST tube
  • Also Acceptable: 4 mL blood in one of
    • Orange RST
    • Lavender (EDTA)
    • Lime Green PST
    • Red Top
  • Pediatric Draw: 1 full Lime Green Microtainer

Note for Pediatric Draw: If ordered at the same time as an Infant Nutrition Panel (INUTP2), 2 microtainers as indicated in the Infant panel are sufficient. No additional microtainers need to be collected.

Handling Instructions
Quantity
requested: 1 mL plasma/serum
minimum: 0.5 mL plasma/serum

Processing

Processing

PST or GOLD SST: centrifuge and refrigerate plasma/serum in original container

LAVENDER or RED top: centrifuge, remove plasma/serum from red cells and refrigerate.

Stability: refrigerated, 7 days.

If samples can’t be analyzed within 7 days: aliquot serum/plasma from spun tube and store at -20C.

NOTE: VITA, VITD and VITE can be run on same aliquot

HMC VITAG and/or VITEG shared sample: place specimen in VITAG/VITEG refrigerated rack.

Performance

LIS Dept Code
Chemistry, Harborview (CHH)
Performing Location(s)
HMC Chemistry, Special
206-520-4600

325 9th Ave, Rm # GWH-47, Seattle, WA 98104-2420

Frequency
Monday - Friday, results available the next day.
Available STAT?
No

Billing & Coding

CPT codes
82306
LOINC
35365-6
Interfaced Order Code
UOW1860