The pre-analytical stability of 25-hydroxyvitamin D: Storage and mixing effects.

ABSTRACT

BACKGROUND: There is an increasing demand for serum 25-OH VitD testing globally, and this has led to the greater use of automated immunoassays. These may be more prone to non-specific interference, that is thought to be related to pre-analytical stability of biological samples. We have investigated the changes in serum 25-OH VitD concentrations that are caused by storage and mixing conditions, and if such changes are statistical, or clinically important. METHODS: Blood samples were collected into plain tubes from 31 healthy donors. After separation, serum samples were stored at -20°C and analysis was carried out with and without mixing (vortexing) at different time intervals of days (0, 1, 2, 3, 4, 5, 15, and 30). All samples were analyzed using a chemiluminescent immunoassay. RESULTS: Mean serum 25-OH VitD concentrations for subsequent days of storage compared with day 0 showed a significant time effect (P < .05) except for the samples on day 1 (P = .654) in non-vortexed samples and day 2 (P = .087), 5 (P = .118) and 30 (P = .118) in vortexed samples. Comparing values for vortexed and non-vortexed samples on the same day, serum 25-OH VitD showed a significant difference on days 1 (P = .003), 4 (P = .037), 5 (P = .002), and 30 (P = .025). However, the maximum change value was 8.85% which was less than the known total allowable error (TEa) and reference change value (RCV) for serum 25-OH VitD. CONCLUSION: 25-OH VitD is pre-analytically stable after long-term sample storage at -20°C and can be analyzed without vortexing. This may be beneficial for both research and diagnostic laboratories.