Vitamin D laboratory testing is crucial for bone and muscle health, preventing chronic diseases, and overall wellbeing. However, developing effective strategies to improve equity in testing requires a strong understanding of volumes, clinical appropriateness and disparities in requests for different population groups.
A new nationwide study by Awanui scientist Leigh Lauv analysed data from over 263,000 vitamin D test results carried out by Awanui Labs across seven regions, between January 2019 and November 2024, which is approximately one test for every twenty New Zealanders.
Leigh’s research examined patterns in vitamin D testing, clinician behaviour, demographics, and what disparities in both testing and deficiency across age, gender and ethnicity shows about the health of communities in Aotearoa New Zealand.
Community-based testing driving the numbers
In the six-year timeframe, vitamin D test volumes rose steadily over the six-year period, both nationally and across all regions. At the same time, while levels remained relatively stable on average, clear variation was seen across different population groups.
“The data shows general practitioners and community-based specialists requested 88 percent of vitamin D test requests, with the remaining 12 percent ordered by hospital clinicians,” says Leigh.
“Between 2019 and 2024, over 10,600 GPs submitted at least one test request, compared with 1,256 hospital clinicians, and 229 community specialists.
“In this time, the average number of tests ordered per GP rose from 6.1 per year to 11.6 in 2024. For community specialists, the average more than doubled from 5.9 to 14.3, while hospital clinicians showed only a slight increase from 5.0 to 5.7 tests per clinician.”
A disproportionate share of testing
Along with the differences in requesting, a critical finding in the study revealed a small number of clinicians were responsible for a disproportionately high number of tests.
“Among those who ordered more than 100 tests during the six years, the average number of requests per clinician was 296, however some individual GPs ordered over 3,000 tests. In contrast, this ranged between 100 and 300 or hospital clinicians and between 200 to 250 for community specialists,” says Leigh.
“One notable finding was just 372 GPs accounted for more than half of all 224,554 community vitamin D tests. This is compared to just 67 hospital clinicians responsible for almost 38 percent of hospital-based tests and nine specialists contributed to over half of all specialist requests.”
Leigh says most patients were tested only once per year though repeat testing became more common over time.
Patients who tested more than once a year typically had more stable vitamin D levels and lower deficiency rates, reflecting ongoing monitoring of known at-risk individuals. Those tested only once per year were more likely to be deficient.
An interesting look at ethnicity and age
“Testing was more common in women, and while men had slightly higher rates of moderate to severe deficiency, age emerged as the most influential factor. Although the 25 to 44 age group accounted for the largest number of vitamin D tests, deficiency was most concentrated in the younger portion of this group. Those aged 35 and over were tested less frequently, and generally had higher vitamin D levels, consistent with age-related improvements seen across the cohort,” says Leigh.
Testing rates increased across all ethnic groups between 2019 and 2024. However, Asian, Pacific, and Māori populations consistently showed higher deficiency rates while European populations had the lowest.
“Deficiency was especially high among young women,” says Leigh. “For example, 28.2 percent of Asian and 21.8 percent of Pacific females aged 15 to 24 were vitamin D deficient. Although levels improved with age, Māori men, and women, and particularly those over 75 continued to show persistently high rates.”
Why the research matters and the path forward
This study provides valuable insight into how vitamin D testing is being used and where improvements could be made.
“The findings confirm some populations at higher risk of deficiency than others, most testing is ordered by community-based clinicians, and a small number of GPs and specialists account for most test requests. This is important for improving test-ordering practices,” says Leigh.
“Supporting clinicians to target vitamin D testing to patients who are genuinely at risk could improve detection while reducing unnecessary testing. But to do this effectively, we need to understand who these patients are, where they live, and ensure clinicians are applying the right criteria at the right time.
“By reaching our most at-risk communities and aligning testing with clinical need, we can support more equitable and effective use of laboratory services and ultimately better health outcomes for patients and communities.”