Table 2.

Mineral metabolism by CKD stage

	Overall	Stage 2 (GFR≥60 ml/min per 1.73 m2)	Stage 3a (GFR=45–59 ml/min per 1.73 m2)	Stage 3b (GFR=30–44 ml/min per 1.73 m2)	Stage 4 (GFR=15–29 ml/min per 1.73 m2)
Number	464	103	127	145	89
GFR, ml/min per 1.73 m2	45 [33, 57]	71 [64, 80]	51 [48, 55]	38 [34, 42]	26 [24, 28]
Serum calcium, mg/dl	9.4±0.4	9.4±0.4	9.4±0.4	9.3±0.4	9.3±0.4
Serum phosphorus, mg/dl	4.6±0.8	4.4±0.7	4.4±0.7	4.6±0.8a	4.9±0.9b,c,d
Serum phosphorus z score, SD	0.1±1.5	−0.4±1.2	−0.2±1.3	0.2±1.5b	0.9±1.8b,c,e
Serum iPTH, pg/ml	51 [30, 84]	37 [26, 54]	48 [26, 70]	55 [33, 95]b	74 [47, 181]b,c,d
Plasma FGF23, RU/ml	138 [91, 210]	93 [73, 140]	122 [90, 171]a	153 [102, 221]b	223 [148, 460]b,c,f
Serum 25OHD, ng/mlg	27±12	27±10	27±11	29±12	25±12
Serum 1,25(OH)2D, pg/mlg	30±11	33±11	32±10	30±12	25±10b,c,e
Urine FEPi, %	16.4 [11.6, 23.2]	10.0 [7.7, 13.6]	14.7 [11.0, 19.2]a	17.8 [13.5, 24.0]a,c	25.2 [20.6, 30.6]a,c,f

Data are means±SD or medians [25th, 75th percentiles]. Differences between CKD stages were tested using one-way ANOVA. P value represents pairwise tests of significance using the Sidak procedure. Analyses of FGF23 and PTH were performed using log-transformed values. iPTH, immunoreactive parathyroid hormone; FGF23, fibroblast growth factor 23; 25OHD, 25-hydroxyvitamin D; 1,25(OH)₂D, 1,25-dihyroxyvitamin D; FEPi, fractional urinary excretion of phosphate calculated as (urine phosphorus×serum creatinine/urine creatinine×serum phosphorus)×100.

^aP<0.05 versus stage 2.

^bP<0.01 versus stage 2.

^cP<0.001 versus stage 3a.

^dP<0.05 versus stage 3b.

^eP<0.01 versus stage 3b.

^fP<0.001 versus stage 3b.

^g25OHD and 1,25(OH)₂D were measured in 376 participants.