This study evaluates the stability of 25-hydroxyvitamin D [25(OH)D] measurements in human serum and plasma using the ALPCO 25(OH) Vitamin D CLIA Kit. The study compares results obtained from fresh specimens with those obtained after storage under various temperature and time conditions, including long-term frozen storage and short-term handling scenarios. The objective is to demonstrate that specimen storage conditions do not result in clinically meaningful differences in measured 25(OH)D concentrations, supporting the use of fresh and previously stored samples in laboratory testing.

This clinical study is designed to assess the analytical stability of 25-hydroxyvitamin D [25(OH)D] in human serum and plasma specimens under defined storage conditions using the ALPCO 25(OH) Vitamin D CLIA Kit, a competitive chemiluminescent immunoassay performed on the KleeYa automated platform.

The study consists of two cohorts. Cohort 1 evaluates long-term stability of 25(OH)D in human serum specimens following storage at ultra-low temperatures (-80°C). Approximately 30 donor-derived serum samples representing clinically relevant vitamin D levels (deficient, insufficient, and sufficient) will be tested at baseline and after storage for predefined time points up to six months. The objective of this cohort is to demonstrate equivalence between fresh and frozen specimens following a single freeze-thaw cycle.

Cohort 2 evaluates short-term stability of 25(OH)D in both serum and plasma specimens under multiple temperature conditions (2-8°C, 22°C, 37°C, and -80°C) over a defined period of up to 31 days. Approximately 10 donor-derived specimens will be tested at baseline and at predefined intervals to assess the impact of sample handling and storage conditions relevant to routine laboratory workflows.

Adult participants (≥22 years of age) will provide a single blood sample collected via standard venipuncture. Specimens will be processed, aliquoted, and tested according to protocol-defined procedures. The primary endpoint is the equivalence of 25(OH)D measurements between fresh and stored specimens. Data analysis will include descriptive and comparative statistical methods, including percent difference and mean bias, to evaluate stability across conditions.

This is a minimal-risk study involving no therapeutic intervention. Results are intended to support analytical performance claims, including specimen handling and storage conditions described in the assay Instructions for Use. No clinical benefit to participants is expected, and study results will not be used for medical decision-making.

Inclusion Criteria:

• Male or female adults 22 years of age or older
• Able and willing to provide a blood sample in accordance with the protocol
• Able to understand the study requirements and provide written informed consent

Exclusion Criteria:

• Unable or unwilling to provide a blood sample
• Current participation in another investigational study that may interfere with study results
• Any condition that, in the opinion of the investigator, would preclude safe participation or compromise the integrity of the study

The study population will consist of adult volunteers from the general population, aged 22 years and older, who are able and willing to provide a blood sample. Participants are expected to represent a range of 25-hydroxyvitamin D [25(OH)D] levels, including deficient, insufficient, and sufficient concentrations. Subjects will be enrolled at clinical collection sites in the United States and will undergo a single blood draw for specimen collection.