Establishment of reference intervals for bone turnover markers in healthy Chinese older adults

Figures & data

Figure 1. Flowchart of the subject selection. BMD: bone mineral density; BTMs: bone turnover markers; BMI: body mass index; T2DM: type 2 diabetes.

Table 1. Reference intervals of P1NP, β-CTX and P1NP/β-CTX for the older adults.

BTMs	Men (n = 946)		Women (n = 881)
	Median	Reference intervals	Median	Reference intervals
P1NP (ng/mL)	40.6	13.6–111.4	49.4	15.8–119.9
β-CTX (ng/mL)	0.184	0.038–0.627	0.243	0.041–0.675
P1NP/β-CTX	230.1	41.0–1269.1	207.7	49.9–1261.5

Reference intervals were defined as the 95% reference value range of all observations (percentile 2.5–97.5). BTMs: bone turnover markers; P1NP: procollagen type I N-terminal propeptide; β-CTX: β cross-linked C-terminal telopeptide of type I collagen.

Figure 2. Reference intervals of P1NP, β-CTX and P1NP/β-CTX in different age groups of the older adults. (a) Male P1NP; (b) Female P1NP; (c) Male β-CTX; (d) Female β-CTX; (e) Male P1NP/β-CTX; (f) Female P1NP/β-CTX.

Table 2. Establishment and comparison of reference values for BTMs between older men and postmenopausal women after stratification by 5 yr increments in the older adults.

Age groups(year)	Sex differences			Reference intervals
P1NP (ng/mL)	Men	Women	p	Men	Women
50–54	42.1(30.5,68.0)	50.1(38.9,70.1)	.031	42.1(13.6–109.7)	50.1(15.6–124.4)
	(n = 96)	(n = 174)		(n = 96)	(n = 174)
55–59	42.9(29.6,70.3)	52.1(31.8,75.9)	.133	42.9(14.2–119.4)	52.1(14.7–119.2)
	(n = 112)	(n = 149)		(n = 112)	(n = 149)
60–64	40.8(30.2,64.3)	49.6(34.4,71.9)	<.001	40.8(11.5–102.0)	49.6(14.7–119.8)
	(n = 206)	(n = 203)		(n = 206)	(n = 203)
65–69	42.1(29.7,61.3)	45.5(35.0,69.4)	.013	42.1(14.6–117.2)	45.5(17.8–121.9)
	(n = 279)	(n = 189)		(n = 279)	(n = 189)
70–74	37.6(28.0,58.9)	46.5(31.2,73.9)	.023	37.6(14.5–108.2)	46.5(15.6–123.8)
	(n = 126)	(n = 103)		(n = 126)	(n = 103)
75–79	39.6(26.9,63.3)	52.2(32.0,70.3)	.175	39.6(13.3–109.6)	52.2(10.3–130.4)
	(n = 91)	(n = 41)		(n = 91)	(n = 41)
β-CTX (ng/mL)
50–54	0.248(0.113,0.369)	0.280(0.177,0.433)	.040	0.248(0.034–0.700)	0.280(0.060–0.689)
	(n = 96)	(n = 174)		(n = 96)	(n = 174)
55–59	0.204(0.125,0.356)	0.234(0.160,0.362)	.176	0.204(0.043–0.680)	0.234(0.032–0.681)
	(n = 112)	(n = 149)		(n = 112)	(n = 149)
60–64	0.196(0.103,0.328)	0.252(0.162,0.374)	<.001	0.196(0.034–0.554)	0.252(0.041–0.696)
	(n = 206)	(n = 203)		(n = 206)	(n = 203)
65–69	0.176(0.117,0.283)	0.206(0.123,0.327)	.059	0.176(0.046–0.594)	0.206(0.035–0.664)
	(n = 279)	(n = 189)		(n = 279)	(n = 189)
70–74	0.174(0.091,0.316)	0.229(0.149,0.391)	.004	0.174(0.038–0.677)	0.229(0.055–0.649)
	(n = 126)	(n = 103)		(n = 126)	(n = 103)
75–79	0.196(0.106,0.300)	0.258(0.181,0.384)	.024	0.196(0.031–0.608)	0.258(0.033–0.683)
	(n = 91)	(n = 41)		(n = 91)	(n = 41)
P1NP/β-CTX
50–54	222.0(127.3,336.5)	179.1(115.0,307.0)	.318	222.0(34.2–929.6)	179.1(38.0–775.8)
	(n = 96)	(n = 174)		(n = 96)	(n = 174)
55–59	197.7(126.0,369.2)	212.6(120.6,349.9)	.956	197.7(36.8–1471.0)	212.6(47.9–1303.4)
	(n = 112)	(n = 149)		(n = 112)	(n = 149)
60–64	226.3(131.7,389.2)	190.8(118.5,365.8)	.170	226.3(42.0–1342.2)	190.8(46.6–1369.4)
	(n = 206)	(n = 203)		(n = 206)	(n = 203)
65–69	252.7(135.1,416.2)	240.2(143.2,443.5)	.939	252.7(40.5–1251.5)	240.2(55.4–1547.4)
	(n = 279)	(n = 189)		(n = 279)	(n = 189)
70–74	243.6(131.0,448.4)	206.3(118.8,335.6)	.137	243.6(36.7–1354.1)	206.3(51.8–1257.5)
	(n = 126)	(n = 103)		(n = 126)	(n = 103)
75–79	213.7(123.1,404.0)	172.3(135.8,356.6)	.600	213.7(41.3–1540.7)	172.3(30.7–1075.6)
	(n = 91)	(n = 41)		(n = 91)	(n = 41)

Reference intervals were defined as the 95% reference value range of all observations (percentile 2.5–97.5). The differences between the two sexes were analysed by Kruskal Wallis test and data are presented as Median (P₂₅, P₇₅).BTMs: bone turnover markers; P1NP: procollagen type I N-terminal propeptide; β-CTX: β cross-linked C-terminal telopeptide of type I collagen; yr: year.

Figure 3. Scatter plots and LOWESS curves of age-dependent BTM levels in older men and postmenopausal women. (a) Male P1NP; (b) Female P1NP; (c) Male β-CTX; d) Female β-CTX; (e) Male P1NP/β-CTX; (f) Female P1NP/β-CTX. The single values (black dots) and the trend lines (blue lines) with 95% confidence intervals (shaded in light blue) shown in the figure were obtained by the LOWESS regression model. BTM-bone turnover markers; LOWESS curve-local weighted regression curves.

Figure 4. Scattered diagram and centile curves of BTM levels against age in older men and postmenopausal women. (a) Female P1NP; (b) Male P1NP; (c) Female β-CTX; (d) Male β-CTX. The 1rd, 5th, 25th, 50th, 75th, 95th and 99th centile curves are shown respectively. BTM-bone turnover markers.

Table 3. Correlations between BTMs and BMD at different skeletal sites.

		P1NP (ng/mL)	β-CTX (ng/mL)	LS BMD (g/cm^2)	FN BMD (g/cm^2)	TH BMD (g/cm^2)
Men
P1NP (ng/mL)	r	–	0.142	−0.099	−0.079	−0.086
	p	–	<.001	.003	.018	.010
β-CTX (ng/mL)	r	0.142	–	−0.157	−0.132	−0.142
	p	<.001	–	<.001	<.001	<.001
P1NP/β-CTX	r	–	–	0.083	0.075	0.081
	p	–	–	.012	.023	.015
Women
P1NP (ng/mL)	r	–	0.174	−0.033	0.018	−0.009
	p	–	<.001	.334	.593	.788
β-CTX (ng/mL)	r	0.174	–	−0.106	−0.070	−0.082
	p	<.001	–	.002	.039	.016
P1NP/β-CTX	r	–	–	0.071	0.060	0.060
	p	–	–	.037	.077	.080

BTMs: bone turnover markers; P1NP: procollagen type I N-terminal propeptide; β-CTX: β cross-linked C-terminal telopeptide of type I collagen; BMD: bone mineral density; LS: lumbar spine; FN: femoral neck; TH: total hip.

Table 4. Multiple linear regression analyses between BMD and other covariates.

Models	Non-standardised coefficient		Standardised partial regression coefficients	P	R^2
	Partial regression coefficient	Standard error
Male LS BMD(g/cm^2)					0.115
Constant	0.673	0.050		<.001
BMI (kg/m^2)	0.020	0.002	0.309	<.001
β-CTX (ng/mL)	−0.159	0.034	−0.147	<.001
Male FN BMD(g/cm^2)					0.129
Constant	0.891	0.050		<.001
BMI (kg/m^2)	0.011	0.001	0.241	<.001
Age (year)	−0.004	0.001	−0.225	<.001
β-CTX (ng/mL)	−0.127	0.024	−0.163	<.001
Male TH BMD(g/cm^2)					0.145
Constant	0.780	0.051		<.001
BMI (kg/m^2)	0.015	0.001	0.319	<.001
β-CTX (ng/mL)	−0.128	0.025	−0.161	<.001
Age (year)	−0.003	0.001	−0.147	<.001
Female LS BMD(g/cm^2)					0.107
Constant	1.088	0.052		<.001
BMI (kg/m^2)	0.010	0.002	0.201	<.001
β-CTX (ng/mL)	−0.075	0.025	−0.095	.004
Age (year)	−0.005	0.001	−0.278	<.001
Female FN BMD(g/cm^2)					0.160
Constant	1.000	0.043		<.001
BMI (kg/m^2)	0.008	0.001	0.183	<.001
Age (year)	−0.006	<0.001	−0.380	<001
β-CTX (ng/mL)	−0.051	0.021	−0.078	.013
Female TH BMD(g/cm^2)					0.209
Constant	1.002	0.041		<.001
BMI (kg/m^2)	0.011	0.001	0.262	<.001
β-CTX (ng/mL)	−0.059	0.020	−0.090	.003
Age (year)	−0.006	<0.001	−0.410	<.001

The BMD in different parts of men and women were used as dependent variables, P1NP, β-CTX and P1NP/β-CTX were used as independent variables, and age and BMI were regarded as covariates, and then multiple linear regression analysis was performed. Only the statistically significant variables in each model were presented in the table (p < .05). β-CTX: β cross-linked C-terminal telopeptide of type I collagen; BMD: bone mineral density; BMI: body mass index; LS: lumbar spine; FN: femoral neck; TH: total hip.