Effect of blood collection tubes on vitamin D immunoassay results.We examined the effect of blood collection tubes on 25-hydroxyvitamin D (25(OH)D) as part of an end-user verification, with approval from the institutional review board (IRB) of Seoul St. Marys Hospital (IRB Number KC23DSSF0058).The following four tubes were examined for potential assay interference: Greiner Bio-One Vacuette 8-mL serum-separator tube (SST) (Greiner Vacuette; Cat. #455071KR, lot #A2309376; Greiner Bio-One, Kremsmunster, Austria), Becton Dickinson (BD) Vacutainer 8.5-mL SST (BD Vacutainer; Cat. #367528, lot #2237485; BD, Franklin Lakes, NJ, USA), AB Medical V-Tube 8-mL tube with clot activator and gel (V-tube; Cat. #301802, lot #8337002; AB Medical, Seoul, Korea), and AB Medical VQ-Tube 8-mL with clot activator with thrombin and gel (VQ-tube; Cat. #B0180B, lot #8B41002; AB Medical).Serum samples from our apparently healthy volunteers (two men and two women; age range, 26-49 yrs) were collected in each of the abovementioned tubes and analyzed for 25(OH)D using the Atellica IM Vitamin D Total assay.Our apparently healthy volunteers (two men and two women; age range, 26-49 yrs) were collected in each of the abovementioned tubes and analyzed for 25(OH)D using the Atellica IM Vitamin D Total assay.Addnl., serum samples of three other apparently healthy individuals were collected in both Greiner Vacuette and VQ tubes for anal.Samples collected in Greiner Vacuette tubes exhibited higher 25(OH)D values (mean bias, 6.22 ng/mL) than those collected in VQ tubes when analyzed with the Siemens Atellica IM system.Our study is limited by its small sample size.Nevertheless, examining various tubes with specimens obtained from healthy individuals is not readily accessible in routine practice, and our findings clearly show the impact of additives in blood collection tubes on vitamin D immunoassay results.