Vitamin D levels are measured in Cystic Fibrosis (CF) to ensure we give optimal supplementation for bone health. Increasingly vitamin D is being implicated not just in bone health but in immunity, muscle function, malignancy and lung function. Children with CF have random vitamin D levels checked during their annual review – do levels vary depending on month of measurement? Is there variation between centres for “normal range” values?
Aim To ensure that all patients have a vitamin D level measured during their annual review and to compare the average level to the average hours of sunlight in the month.
Method Patients were selected from the local CF database and the local pathology system was checked for vitamin D levels. These were then compared to average hours of sunlight in the month. We also surveyed the local biochemistry laboratories to compare reference values for vitamin D.
Results We identified 25 paediatric and 24 adult patients eligible for our audit. All the paediatric patients had a vitamin D level measured as part of their annual review, one adult patient did not. Average vitamin D levels showed a relationship to the average hours on sunlight in the month (figure 1). 66% vitamin D levels were suboptimal, although they were adequate between April and October. As a measure of compliance Vitamin A and E levels were also measured which remained relatively constant throughout the year.
Conclusion Of the 49 patients identified only one did not have a vitamin D measured. Vitamin D levels varied in relationship to the average hours of sunlight in that month. A literature search found several papers relating to the vitamin D and season, however none suggested optimal time of year for measurement. Of the 5 local laboratories surveyed all had different reference ranges for vitamin D and only one had an upper limit (table 1). In view of our findings we suggest that we should be prepared to supplement patients with a low normal level in the summer months more than those with a low normal level in the winter months.