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. Author manuscript; available in PMC: 2010 Feb 1.
Published in final edited form as: Ann Epidemiol. 2008 Mar 10;19(2):73–78. doi: 10.1016/j.annepidem.2007.12.001

FIG. 4.

FIG. 4

Laboratory personnel basal serum 25(OH)D concentration. A, In these 10 individuals, the mean serum 25(OH)D varied widely [from 17.1 (4.6) to 35.6 (5.2) ng/ml; P < 0.005] between laboratories (error bars represent SEM). B, Similarly, marked within-individual variation was observed in 25(OH)D measurement in different laboratories. Whether an individual has hypovitaminosis D (arbitrary threshold, 32 ng/ml shown as dashed line) depends on which laboratory was used. Note that laboratory H used HPLC and was considered to be the “gold standard” against which others were compared. Reproduced with permission.33