Comparing Vitamin D Results and Acceptability of Sampling Obtained From Dried Blood Spot, Tasso+ Capillary Sampling, and Venous Blood.

This study will evaluate the performance and acceptability of different sampling methods for measuring vitamin D, specifically 25-hydroxyvitamin D₂ and 25-hydroxyvitamin D₃.

Inclusion Criteria: * Adults aged 18 years or older. * Current healthcare staff or staff volunteers. * Already consented to use the routine dried blood spot (DBS) vitamin D service. * Able and willing to provide all three sample types- routine DBS finger-prick sample, a Tasso+ upper-arm self-collected capillary sample, and a venous blood sample taken by a trained Trust phlebotomist. * Able to give informed consent. * Able to complete a short questionnaire in English. Exclusion Criteria: * • Participants will not be able to take part if any of the following apply: * Under 18 years of age * Not a member of staff or staff volunteer * Known difficulty with blood sampling, such as a history of fainting, severe needle phobia, or conditions that make venepuncture unsafe. * Skin conditions or injuries on the upper arm that would prevent safe use of the Tasso+ device. * Bleeding disorders or current use of anticoagulant medication that would make capillary or venous sampling unsafe. * Inability to give informed consent, including difficulty understanding the study information. * Inability to complete the short questionnaire in English, as this is needed to assess user experience.