Vascular Calcification and Bone Mineral Density in Recurrent Kidney Stone Formers

Linda Shavit; Daniela Girfoglio; Vivek Vijay; David Goldsmith; Pietro Manuel Ferraro; Shabbir H. Moochhala; Robert Unwin

doi:10.2215/CJN.06030614

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Figure 1.
Distribution of AAC score in KSFs and healthy controls. The plot shows the distribution of AAC score in participants with and without stones. In the multivariate model adjusted for age, sex, high BP, diabetes, smoking status, and eGFR, the relationship between AAC severity score and kidney stone disease remained significant (P<0.001). The bottom and top of the box represent the first and third quartiles, the line represents the second quartile (median), the whiskers represent 1.5 times the interquartile range of the first and third quartiles, and the circles represent any values lying outside the whiskers. AAC, aortic calcification; KSF, kidney stone former.
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Figure 2.
Distribution of CT BMD in KSFs and healthy controls. The plot shows the distribution of CT BMD in participants with and without stones. In the multivariate model adjusted for age, sex, high BP, diabetes, smoking status and eGFR, the relationship between osteoporosis and kidney stone disease remained significant (P<0.001). The bottom and the top of the box represent the first and third quartiles, the line represents the second quartile (median), the whiskers represent 1.5 times the interquartile range of the first and third quartiles, and the circles represent any values lying outside the whiskers. BMD, bone mineral density; CT, computed tomography.
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Figure 3.
Distribution of urinary excretion of calcium among KSFs with and without vascular calcification. Urinary excretion of calcium was roughly similar among patients with and without an AAC score >0 (median 280 mg/d [120, 400] versus 288 mg/d [140, 360], P=0.86).The bottom and the top of the box represent the first and third quartiles, the line represents the second quartile (median), and the whiskers represent 1.5 times the interquartile range of the first and third quartiles.

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Table 1.

Baseline clinical characteristics of the patients in the two study groups

Clinical Characteristic	KSFs (n=57)	Non-KSFs (n=54)	P Value
Age, yr	47±14	47±13	0.82
Men	32 (56)	31 (57)	0.89
Comorbidities^{^a}
Systemic hypertension	17 (35)	5 (9)	0.002
Diabetes mellitus	5 (10)	1 (2)	0.07
Smoking^b	4 (12)^{^b}	16 (30)	0.06
Laboratory results
Sodium, mEq/L	141±2	143±2	0.02
Potassium, mEq/L	4.3±0.3	4.4±0.3	0.20
Calcium, mg/dl	9.4±0.4	9.6±0.4	0.26
Phosphorus, mg/dl	3.1±0.6	3.4±0.6	0.04
Magnesium, mg/dl	0.84±0.12
Uric acid, mg/dl	5.5±1.3
Urea nitrogen, mg/dl	16±5.9	14.8±2.8	0.58
Creatinine, mg/dl	1±0.4	0.9±0.1	0.45
eGFR, ml/min^–1 per 1.73 m^–2	91±22	91±15	0.31
Bicarbonate, mEq/L	26±2	25±2	0.02
Glucose, mg/dl	88±18	93±18	0.08
Albumin, g/L	46±3	47±3	0.66
Parathyroid hormone (range, 1.6–6.9 pmol/L)	4.3 (3.1, 6.9)
25(OH)vitamin D, nmol/L	43 (28, 64)
24-h urine collection (n=36)
Volume, liters	2.0±0.9
Sodium mEq/d	156±46
Potassium, mEq/d	69±20
Calcium, mg/d	280 (124, 400)
Phosphorus, mg/d	806±270
Oxalate, mg/d	30±7.2
Uric acid, mg/d	584±150
Citrate, mg/d	420 (360, 670)
Creatinine, mg/d	1144±352

Data are presented as the mean ± SD, n (%), or median (25th percentile, 75th percentile). KSF, kidney stone former.
↵a Comorbidity data were available in 50 KFSs.
↵b Smoking history was available in 24 KFSs.

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Table 2.

Incidence of vascular calcification and osteoporosis in KSFs and healthy non-stone formers as detected by the unadjusted analyses

Group	KSFs (n=57)	Non-KSFs (n=54)	P Value
Patients with AAC	22/57 (38)	19/54 (35)	0.69
Men	9/31 (28)	9/31(29)
Women	12/23 (52)	10/23 (43)
Median AAC score^a	0 (0, 43)	0 (0, 10)	<0.001
Patients with osteoporosis^{^b}	16/51 (31)	9/54 (17)	0.11
Men	5 (9.8)	4 (14)
Women	7 (14)	5 (9)
Average CT BMD, HU	159±53	194±48	<0.001

Data are presented as n (%) unless otherwise indicated. AAC, abdominal aortic calcification; CT, computed tomography; BMD, bone mineral density; HU, Hounsfield unit.
↵a AAC score, which was not normally distributed, is shown as the median (25th percentile, 75th percentile).
↵b Osteoporosis is defined as CT attenuation <135 HU at the L1 level. In the KSFs, data were available in 51 patients.

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Table 3.

Results of regression models for the estimated difference in AAC or CT BMD between KSFs and non-stone formers

Analysis	Difference (95% Confidence Interval)	Akaike Information Criterion	P Value
AAC
Univariate	3.56 units (3.39 to 3.78)	631.03	0.01
Multivariate	3.78 units (3.53 to 4.06)	445.88	<0.001
CT BMD
Univariate	−34.58 HU (−53.85 to −15.32)	1110.70	<0.001
Multivariate	−35.88 HU (−55.95 to −15.82)	870.63	<0.001

Multivariate models are adjusted for age, sex, high BP, diabetes, smoking status, and eGFR. The r² statistics are not presented because the model for AAC is a zero-inflated negative binomial and does not allow r² computation. The Akaike information criterion is presented as a similar measure of fit.