Free 25OH Vitamin D instead of Total 25OH Vitamin D

the additional value of testing

Currently, Free T4 (thyroid hormone) measurements are well established in clinical diagnostics. Free T4 measurements, which reflect both total T4 levels and binding protein capacity, have become the recognized standard for determining thyroid status in conjunction with a TSH measurement.
Similarly, in several conditions such as pregnancy, renal disease or liver disease the level of Vitamin D binding proteins may be elevated or decreased. Recent literature suggests that particularly in these cases free 25OH Vitamin D might be a better indicator of Vitamin D status. It provides more relevant diagnostic information than measurement of Total 25OH Vitamin D.

Clinical Utility


The monitoring of Vitamin D deficiency during pregnancy is very important and has become a general practice in many countries.
Fetal needs for vitamin D increase during the latter half of pregnancy, when bone growth and ossification are most prominent. Vitamin D is transported to the fetus by passive transfer, and the fetus is entirely dependent on maternal stores. Therefore, maternal status is a direct reflection of fetal nutritional status.
Due to a fast and large increase in the concentration of the Vitamin D Binding Protein during pregnancy Total 25OH Vitamin D levels rise concomitantly. The concentration of Free 25OH Vitamin D remains the same or even decreases.
Recent research has shown that the measurement of free 25OH Vitamin D during pregnancy is a better marker of Vitamin D status than measurement of total vitamin D and should be implemented in the clinical laboratories.

Renal Disease

The monitoring of Vitamin D deficiency during Chronic Kidney Disease (CKD) and Dialysis or End Stage Renal Disease (ESRD) is very important. It has become a general practice in many countries. Total 25OH Vitamin D is typically measured annually in patients with CKD stage 3-4. Even more frequently if the supplementation strategy does not increase the 25OH Vitamin D concentrations as expected.
As kidney function worsens, low circulating Vitamin D levels can lead to secondary hyperparathyroidism (SHPT). In addition, Vitamin D may play a role in complications of CKD, including hypertension, left ventricular hypertrophy and diastolic dysfunction, albuminuria, vascular calcification and infection.
Due to a decrease in the concentration of the Vitamin D Binding Protein during nephrotic syndrome the measurement of total 25OH Vitamin D is no longer a good representation of the Vitamin D status.

Liver Disease

In patients with liver failure, the levels of 25OH Vitamin D can be low due to impaired synthesis. Examples of liver failure are cirrhosis, hepatitis, Epstein Barr virus (infectious mononucleosis), non-alcoholic fatty liver disease. Liver disease could also lead to impaired absorption of Vitamin D. This is possibly connected to impaired bile acid production or gut edema associated with portal hypertension. Levels of Vitamin D binding protein may be decreased.
Low vitamin D levels and bone disease are well-recognized complications of “cholestatic” liver disease. It decreases the production or flow of bile. More recently, studies have confirmed low Vitamin D levels in non-cholestatic liver disease.

Many post-transplant patients are also prone to accelerated bone loss, which could be worsened by Vitamin D deficiency. Dangerously low levels of Vitamin D may also increase some side effects of interferon therapy, such as muscle aches. There are some reports of hepatitis C patients with Vitamin D deficiency responding poorly to interferon therapy.
Therefore, it is recommended that all hepatologists should monitor Vitamin D levels and treat deficient patients.
Due to a decrease in the concentration of the Vitamin D Binding Protein during liver failure the measurement of total 25OH Vitamin D is no longer a good representation of the concentration of the vitamin D status.

Free Vitamin D on automated platforms

Missing free 25OH Vitamin D in the menu on your Automated Platform? Future Diagnostics Solutions can implement the assay on your platform. We developed Total Vitamin D assays on automated immunoassay platforms showing the highest level of specificity, sensitivity and precision found in the market for large multinational IVD companies.

Free 25OH Vitamin D ELISA

Future Diagnostics Solutions B.V. developed the free 25OH Vitamin D ELISA in collaboration with DIAsource ImmunoAssays S.A. This is a competitive ELISA two-step immunoassay. It allows a direct measurement of the concentration of free 25OH Vitamin D in serum. This ELISA assay is unique and exclusively available at DIAsource.

A free 25OH Vitamin D assay on your automated platform?