Table 3.

The difference in the serum concentration of free 25(OH)D and the free fractions between participants with vitamin D deficiency vs vitamin D sufficiency.

	Vitamin D deficiency (total serum 25(OH)D <25 nmol/L)	Vitamin D Sufficiency (total serum 25(OH)D ≥75 nmol/L)	SignificanceP-value
	N = 25	N = 152
	Mean ± s.d.	Mean ± s.d.
Directly measured free 25(OH)D in serum (pmol/L)	5.6 ± 0.82	16.4 ± 4.1	<0.001
Calculated free 25(OH)D in serum (pmol/L)	7.4 ± 3.1	28.3 ± 11.4	<0.001
The percentage of free 25(OH)D (%) (using directly measured free 25OHD)	0.031 ± 0.007	0.017 ± 0.003	<0.001
The percentage of free 25(OH)D (%) (using calculated free 25(OH)D)	0.039 ± 0.015	0.030 ± 0.010	0.005
Serum DBP (mg/L)	203.4 ± 70.6	272.0 ± 86.0	<0.001
Serum albumin (g/L)	41.9 ± 3.2	41.5 ± 4.3	0.646
Serum 1,25 (OH)2D (pmol/L)	80.5 ± 25.5	129.2 ± 47.4	<0.001
Serum iPTH (ng/L)	62.0 ± 32.4	38.7 ± 17.0	0.002

1,25(OH)₂D, 1,25-dihydroxy vitamin D; 25(OH)D, 25-hydroxy vitamin D; DBP, vitamin D binding protein; iPTH, intact parathyroid hormone.