The end of winter is the ideal time to test patients for vitamin D deficiency
By Dr Wessel Jenner
Published June 2021
Vitamin D levels fluctuate significantly depending on the season. At the end of winter, approximately 36% of Australians are vitamin D deficient, in comparison to 14% at the end of summer. This makes the end of winter the best time to test patients for vitamin D deficiency.
Target vitamin D levels
The international recommendations for adequate vitamin D levels vary. However, based on a review of current literature and recently published recommendations1, 2, Clinical Labs suggests that an adequate vitamin D status is a serum level equal to or greater than 50 nmol/L at the end of winter. This level should be 10-20 nmol/L higher at the end of summer to allow for seasonal decrease.This figure is based on the level below which parathyroid hormone (PTH) concentrations begin to rise and the risk of fractures increases.As for all tests, Australian Clinical Labs’ pathologists and scientists will continue to evaluate current literature, and our target range may change as new evidence emerges.
Who to test
Vitamin D testing should be ordered for patients at risk of vitamin D deficiency, including:
- Housebound people - including the sick and disabled
- Elderly in high care
- People with darker skin
- People who cover their skin due to religious or cultural reasons
- People who regularly avoid the sun
- People who work indoors
- Vegetarians
Also patients with:
- Signs, symptoms, and/or planned treatment of osteoporosis or osteomalacia
- Proximal muscle weakness
- Increased alkaline phosphatase (ALP) with otherwise normal LFTs
- Hyperparathyroidism, hypo- or hypercalcaemia, or hypophosphataemia
- Malabsorption (i.e., CF, IBD, coeliac, etc.)
- Medications known to decrease vitamin D levels (e.g., anticonvulsants)
- CRF and transplant recipients
Further testing
When ordering a vitamin D test for a patient, also ordering a serum calcium assessment and parathyroid hormone test, will assist in placing the vitamin D level within the context of overall calcium homeostasis. If osteoporosis is present, fasting blood crosslaps (CTX) will provide a way of monitoring bone turnover in response to therapy.
Treatment
If patients are unable, for a variety of reasons, to gain the required amount of sun exposure for vitamin D production, supplementation may be required.
A maintenance dose of up to 1000 IU/day may be adequate, however some individuals will require higher doses. Severe vitamin D deficiency (serum level <20 nmol/L) may require 3,000-5,000 IU/day for 6 to 12 weeks.
Serum 25-OHD should be retested no earlier than 3 months following commencement of supplementation with vitamin D or a change in dose. Once a desirable target has been achieved, especially at the end of winter, no further testing is required unless risk factors change2.1.
References
- Vitamin D and health in adults in Australia and New Zealand: a position statement. MJA 196(11), 18 June 2012.
- RCPA Position Statement: Use and Interpretation of Vitamin D testing. The Royal College of Pathologists of Australasia, May 2013
About the Author
Dr Wessel Jenner
BSc MBChB FRCPA- Chemical Pathology
- Vitamin D Testing
- Diabetes Management
- Thyroid Function
- Hormone Testing
Dr Jenner began training in Chemical Pathology in 2001 and obtained Fellowship from the Colleges of Medicine of South Africa in 2004, as well as a Master’s degree in Chemical Pathology from the University of Pretoria in 2005. He has worked as a senior registrar in Clinical Biochemistry at the Royal Infirmary of Edinburgh, as a consultant clinical biochemist at the NHS Borders Hospital (Scotland), and as a consultant chemical pathologist in private practice in South Africa. In 2012, Dr Jenner relocated to Australia and worked as a senior registrar at the Royal Brisbane and Women’s Hospital. He obtained his Fellowship from the Royal College of Pathologists of Australasia in 2013 and joined Australian Clinical Labs in early 2014.