Test: 1,25-dihydroxvitamin D (1,25-D)

Also known as 1,25-dihydroxyvitamin DPrimary biologically active vitamin D hormone. Activates the vitamin D nuclear receptor. Produced by hydroxylation of 25-D. Also known as 1,25-dihydroxycholecalciferol, 1,25-hydroxyvitamin D and calcitirol., 1,25-D is the active form of vitamin D, binding to and activating the Vitamin D Nuclear ReceptorA nuclear receptor located throughout the body that plays a key role in the innate immune response. (VDR). 1,25-D is classified as a secosteroid and is tightly regulated by the body as are all the other hormones.1) For example, one study showed that patients given 800 IU/day of vitamin D for six weeks did not show any increase in blood levels of 1,25-D.2)

When activated, the VDR transcribes hundreds of genes including those necessary for innate immune function, the body's first line of defense against pathogens.

Growing evidence suggests that:

Note that when researchers or journalists talk about vitamin D deficiency, they are invariably talking about low levels of 25-D as opposed to 1,25-D.

When to test 1,25-D

A cohort of 100 patients was shown to have significantly (p<0.0001) higher serum levels of 1,25-D compared to the standard range. This data was described in Dr. Greg's Blaney's 2008 presentation at the International Congress on Autoimmunity in Portugal

In the context of the Marshall Protocol (MP), a 1,25-D test is largely useful at a single point in time: prior to beginning the therapy and as a general measure of overall inflammationThe complex biological response of vascular tissues to harmful stimuli such as pathogens or damaged cells. It is a protective attempt by the organism to remove the injurious stimuli as well as initiate the healing process for the tissue.. After starting the MP, regular dosing of olmesartan (Benicar) cuts levels of 1,25-D by as much as 50% in a week's time.

Of special note for women

By their nature, levels of 1,25-D naturally fluctuate. Women who are interested in knowing their highest level of 1,25-D should have their blood drawn mid-cycle around Day 15 or so. This is at least according to one very small 1982 study, which demonstrated that the serum concentration of 1,25-D fluctuated with the menstrual cycle.3) Levels of 1,25-D were shown to be dramatically higher near ovulation in women not on the pill.

The higher the level, the more persuasive the evidence of Th1 inflammationThe complex biological response of vascular tissues to harmful stimuli such as pathogens or damaged cells. It is a protective attempt by the organism to remove the injurious stimuli as well as initiate the healing process for the tissue. will be for a doctor.

How to test 1,25-D

MP patients getting their 1,25-D levels tested should ensure the relevant instructions are closely followed including the freezing of blood samples. Over the course of at least 72 hours, 1,25-D does not appear to be degraded to any significant degree when stored at 24°C.4)

Interpreting a 1,25-D test

Contextual interpretation of a patient's 1,25-D result is available through the vitamin D calculator.

Units of measurement

On the Marshall Protocol study site, 1,25-D levels are typically discussed using pg/ml units rather than pmol/L. The ratio between the two units is: 1 pg/ml = 2.4 pmol/L. To convert pmol/L into pg/ml, multiply by 0.42, as you see in this example:

72 pmol/L * 0.42 = 30 pg/ml

This is also done automatically with the vitamin D metabolite calculator.

Reference range for 1,25-D

Some laboratories establish a “normal” range for the D metabolites results based on the average of all the “healthy” persons who are tested. Since Th1 inflammation is under-diagnosed, the lab ranges are skewed high because it is assumed that it is normal for some people (who are actually sick) to have a level as high as 60 pg/ml. Therefore, many labs provide “normal” ranges for 1,25-D that are strongly skewed above a more accurate normal level.

Larger more reliable studies have found that healthy people have lower levels of 1,25-D than standard reference ranges might otherwise suggest.

  • The largest and most reliable published study identifying a valid 1,25-D reference range is a Danish population study.5) For non-smokers, the average 1,25-D level was 29.0 pg/ml ± 9.5 pg/ml.
  • A small study confirms these lower values when reporting a mean of 23.6 ± 1.3 pg/ml for 1,25-D in controls.6)

These ranges are consistent with levels measured from 1,700 patients at the University of Toronto and the Merck's Physicians' Handbook.

In healthy persons, levels are 25 to 40 ng/ml (62.4 to 99.8 nmol/L) for 25(OH)D3 and 20 to 45 pg/ml (48 to 108 pmol/L) for 1,25(OH)2D3. In nutritional rickets and osteomalacia, 25(OH)D3 levels are very low, and 1,25(OH)2D3 is undetectable. A low serum phosphorus (normal: 3.0 to 4.5 mg/dL [0.97 to 1.45 mmol/L]) and a high serum alkaline phosphatase are characteristic. Serum calcium is low or normal, depending on the effectiveness of secondary hyperparathyroidism in restoring serum calcium to normal. Serum PTH is elevated, and urinary calcium is low in all forms of the disease except those associated with acidosis. In hereditary vitamin D-dependent rickets, laboratory findings vary.

Merck Manual of Diagnosis and Therapy, 15 Oct 2006 7)

Validity of the 1,25-D test and alternatives

Variability in levels of 1,25-D somewhat compromises the validity of a serum 1,25-D test as an absolute measure for disease state. For this reason, candidates for the MP are advised that the ultimate measure for suitability for the MP is the therapeutic probe.

In addition, since the introduction of the Marshall Protocol, the actual 1,25D test performed by laboratories has been modified and may not be picking up the same factors as were being detected in patients with Th1 illness by the prior testing method.

Read more

Notes and comments


Seasonal variation of 1,25-dihydroxyvitamin D and its association with body mass index and age.
Moan J, Lagunova Z, Lindberg FA, Porojnicu AC
J Steroid Biochem Mol Biol113p217-21(2009 Feb)
Fluctuation of serum concentration of 1,25-dihydroxyvitamin D3 during the menstrual cycle.
Gray TK, McAdoo T, Hatley L, Lester GE, Thierry M
Am J Obstet Gynecol144p880-4(1982 Dec 15)
Stability of vitamin D metabolites in human blood serum and plasma.
Lissner D, Mason RS, Posen S
Clin Chem27p773-4(1981 May)
The influence of smoking on vitamin D status and calcium metabolism.
Brot C, Jorgensen NR, Sorensen OH
Eur J Clin Nutr53p920-6(1999 Dec)
The Merck Manual of Diagnosis and Therapy no longer provides this information regarding 1,25-D online.
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