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.