Table 2.

Impact of centrifuging time and type of collection tube on 25-hydroxyvitamin D concentrations, according to type of assay

	CLIA/LIAISON®†			DiaSorin RIA†
	β Coefficient	(95% CI)	p-Value	β Coefficient	(95% CI)	p-Value‡
Centrifuging time
2 h	Referent		0.63	Reference		0.05
24 h	0.008	(−0.068, 0.083)		0.011	(−0.066, 0.088)
72 h	−0.041	(−0.106, 0.025)		0.052	(0.012, 0.092)
96 h	0.007	(−0.049, 0.056)		0.026	(−0.028, 0.080)
Collection tube
No additive—serum	Referent		0.05§	Reference		0.21
Heparin—plasma	0.054	(0.011, 0.096)		0.019	(−0.006, 0.043)
EDTA—plasma	−0.002	(−0.071, 0.066)		−0.034	(−0.096, 0.027)

β coefficient from generalized estimating equations (GEE) linear regression models; 25-hydroxyvitamin D concentrations were log-transformed

Abbreviations used CLIA Chemiluminescence immunoassay; RIA Radioimmunoassay

^†Model adjusted for centrifuging time and collection tube

^‡Two-sided p-value from the omnibus test

^§Pair-wise test: heparin versus serum, p = 0.01; heparin versus EDTA, p = 0.08