T50 is a novel serum-based marker that assesses the propensity for calcification in serum. A shorter T50 indicates a greater propensity to calcify and has been associated with cardiovascular disease and mortality among patients with chronic kidney disease. The factors associated with T50 and the correlation between T50 and bone mineral density (BMD) are unknown in hemodialysis (HD) patients.
This cross-sectional study included 184 patients undergoing HD. Individuals were grouped into tertiles of T50 to compare the demographic and disease indicators of the tertiles. Linear regression was used to evaluate the association between T50 and hip and spinal BMD in a multivariate model.
Mineral and inflammatory parameters, including serum phosphate (r = –0.156, p = 0.04), albumin (r = 0.289, p < 0.001), and high-sensitivity C-reactive protein (r = –0.224, p = 0.003) levels, were associated with T50. We found a weak association between T50 and BMD in the total hip area in the unadjusted model (β = 0.030, p = 0.04) but did not find a statistically significant association with the total hip (β = 0.017, p = 0.12), femoral neck (β = –0.001, p = 0.96), or spinal BMD (β = 0.019, p = 0.33) in multivariable-adjusted models.
T50 was moderately associated with mineral and inflammatory parameters but did not conclusively establish an association with BMD in HD patients. Broad-scale future studies should determine whether T50 can provide insights into BMD beyond traditional risk factors in this population.
Chronic kidney disease (CKD)-mineral bone disease (MBD) is a common complication of CKD that is associated with morbidity and mortality. Several studies have suggested an interconnection between vascular calcification, impaired bone and mineral metabolism, and increased mortality [
T50 has been proposed as a potential novel serum-based marker for assessing calcification propensity [
Although vascular calcification and bone health are intercorrelated and are known risk factors for predicting cardiovascular events (CVE) in dialysis patients, the association between T50 and BMD in dialysis patients with a high CVE risk is not well understood. As renal function decreases in CKD patients, mineral parameters are perturbed and related to bone and vascular health, which is an important pathophysiology of CKD-MBD [
In the past, routine BMD evaluation was not recommended in CKD patients [
Therefore, in this study, we aimed to provide the first analysis of the clinical and biochemical parameters of T50 in patients undergoing HD. We also examined the relationships between T50, BMD from the various sites, and mineral and inflammatory parameters, to evaluate the potential of T50 as a predictor of the CKD-MBD association in HD patients.
This study was based on maintenance HD patients from a single center in Korea. We investigated the associations between T50, BMD, and biochemical parameters using a cross-sectional design.
A total of 184 patients who visited our HD unit at the Gachon University Gil Medical Center between March 2020 and February 2021 were analyzed. Patients were enrolled in the study if they 1) had been on HD for at least 3 months, 2) agreed to participate in the study with written informed consent, and 3) were free of any complications that could affect serum T50 and other biochemical parameters such as an indwelling catheter, any underlying malignancy, active liver disease, current infection, or previous parathyroidectomy.
This study adheres to the Declaration of Helsinki and was approved by the Institutional Review Board at the Gachon University Gil Medical Center (No. GBIRB2020-342). Written informed consent was obtained from all participants.
All demographic and clinical data, comorbidities, laboratory values, and medications were collected at the time of enrollment from participants’ medical records by a well-trained study coordinator. The following baseline demographic and clinical characteristics were collected: age, sex, body mass index, smoking, and HD duration. Data on comorbidities, including hypertension (HTN), diabetes mellitus (DM), CVD such as angina pectoris, myocardial infarction, heart failure (HF), transient ischemic attack (TIA), stroke, and peripheral arterial disease, were also collected. Angina pectoris and myocardial infarction were defined as the presence of coronary artery disease as documented by angiography, an acute coronary syndrome, angina requiring percutaneous coronary intervention, or coronary artery bypass grafting surgery. Stroke and TIA were defined as cases where magnetic resonance imaging was performed on patients with suspected symptoms that were diagnosed by a neurologist. Systolic HF was defined as left ventricular ejection fraction of <40%, and diastolic HF was defined as E/é of >15. All blood samples were obtained prior to a mid-week HD session after overnight fasting and microcentrifugation for measurements. Serum was separated from blood samples within 1 hour of collection and stored at −70°C until analysis. Laboratory data included the single-pool Kt/V (spKtV), hemoglobin, albumin, protein, calcium, phosphorus, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, parathyroid hormone, alkaline phosphatase (ALP), total cholesterol, triglyceride (TG), and high-sensitivity C-reactive protein (hsCRP). Medication data included the use of renin-angiotensin-aldosterone system blockers, calcium channel blockers, β-blockers, phosphate binders, statin, vitamin D analogues, and cinacalcet.
T50 was determined using a nephelometer (Nephelostar; BMG Labtech, Offenburg, Germany), which measures the time-point transformation from primary to secondary CPP, as described in a previous study [
The BMD was estimated using a dual-energy X-ray absorptiometry system (Hologic, Marlborough, MA, USA). The BMD of the total hip, femoral neck, and lumbar spine (L1–L4) were measured at baseline, and the results were expressed as density (g/cm2) and T-scores (standard deviation [SD] from the average BMD value in a healthy young population).
Plain X-ray images of the lateral lumbar spine from all subjects were studied to calculate semiquantitative abdominal aortic calcification (AAC) scores, as described by Kauppila et al. [
Continuous variables were tested for normality using the Shapiro-Wilk test before further statistical analysis. Variables without a normal distribution were either transformed into a logarithmic scale and then subjected to parametric tests or analyzed using a non-parametric test. Values with a normal distribution are expressed as mean ± SD, while those without a normal distribution are presented as median and interquartile range. Comparisons between the groups were performed using the chi-square test, Student t test, or analysis of variance with Tukey multiple comparison test as appropriate. Correlation between two continuous variables was analyzed using Pearson correlation test. Variables that do not show a normal distribution were analyzed by converting them to logarithmic values. Independent variables associated with T50 were identified using multiple stepwise linear regression analysis. All statistical analyses were conducted using R software, version 3.5.3 with packages (The Comprehensive R Archive Network;
Participant demographics and clinical characteristics stratified by tertiles of T50 concentration are shown in
T50 showed a significant correlation with the total hip T-score (r = 0.158, p = 0.038) (
We compared the mean T-score of BMD according to the sites at which it was assessed (
BMD showed an inverse correlation with age and the spKtV (lumbar: r = –0.310, p < 0.001; femoral neck: r = –0.403, p < 0.001; total hip: r = –0.440, p < 0.001) and a positive correlation with albumin (lumbar: r = 0.094, p = 0.218; femoral neck: r = 0.201, p = 0.008; total hip: r = 0.219, p = 0.004). Only the L spine BMD showed an inverse correlation with ALP (r = –0.225, p = 0.003). Femoral neck (r = –0.267, p < 0.001) and total hip BMD (r = –0.176, p = 0.021) also showed an inverse relationship with AAC scores (
We used linear regression to evaluate the cross-sectional association between T50 and femoral neck, hip, and spinal BMD. We found no statistically significant associations between T50 and femoral neck or lumbar spine BMD in either the unadjusted models (femoral neck: β = 0.005, p = 0.708; lumbar spine: β = 0.032, p = 0.101) or in the adjusted models (femoral neck: β = –0.001, p = 0.956; lumbar spine: β = 0.019, p = 0.331) (
We found a weak association between T50 and BMD in the total hip area in the unadjusted model (β = 0.030, p = 0.043) but did not find a statistically significant association in the multivariate-adjusted models (β = 0.017, p = 0.188) (
In this cross-sectional study of HD patients, T50 was associated with mineral and inflammatory parameters but not with AAC score or BMD.
CKD-MBD is a common complication of CKD and is associated with morbidity and mortality. The interconnection between vascular calcification and bone health has been reported as a significant inverse relationship between vascular calcification and bone fragility (low BMD) [
Reduced serum T50 is associated with a lack of inhibitors and abundant promoters of vascular calcification [
The main determinants of T50 in this study were inflammatory (serum albumin and hsCRP), mineral (serum phosphate), and the bone turnover marker (ALP). Only the values measured in the BMD total hip joint area showed a weak correlation in the unadjusted model, but there was no association with BMD measured in all regions in the multivariable-adjusted models. This finding is consistent with epidemiological data in advanced CKD-ND cohorts, where reduced T50 has been correlated with increased phosphate, decreased albumin, and CPP-associated fetuin-A concentration [
Recently, an association between T50 and BMD was reported in 150 non-CKD participants from an elderly male cohort [
A lower T50 was significantly associated with the severity and progression of coronary artery calcification in patients with CKD-ND; however, T50 was not associated with the incidence of coronary artery calcification [
The propensity for serum calcification reflects the degree of activity of numerous humoral and cellular factors that affect the formation and growth of calcified crystals in blood vessels [
The T-score of BMD showed slightly different results depending on the measurement location, with the lowest values at the femur neck, the highest values at the lumbar spine, and a moderate level at the total hip. When studying the relationship between BMD and vascular calcification, there is currently no consensus as to which specific bone location should be the representative for BMD measurement [
Osteoporosis causes both cortical and trabecular bone loss, whereas CKD-MBD results in primarily cortical bone loss [
This study has some limitations. First, a causal relationship could not be confirmed by conducting a cross-sectional study. However, we performed correlation analyses with various mineral parameters; in particular, we evaluated BMD in a relatively large number of HD patients, described its distribution, and analyzed its association with T50. Second, we were unable to control the dialysis protocol and medications that affected T50 measurements. However, considering that the characteristics of dialysis patients are always affected by medication as well as dialysis itself, we need to carefully consider the evaluation value of T50 in future.
In summary, for the first time in Korea, we have provided a stable measurement method for T50 and applied it to clinical research. T50 was correlated with mineral and inflammatory parameters but not with AAC. BMD was correlated with T50 in the case of total hip but was not correlated with BMD measured at other sites (femoral neck and lumbar spine). To evaluate the value of T50 as a predictor of CKD-MBD diagnosis and treatment in ESKD patients, a study on its association with hard outcomes, including fracture, CVE, and mortality, should be prioritized. In addition, to confirm the association between T50 and dynamic changes such as vascular calcification or BMD changes, a large-scale study that includes a larger number of patients and a longer observation period is needed.
All authors have no conflicts of interest to declare.
This work was supported by Gachon University Gil Medical Center (grant No. FRD2020-12 to JYJ) and by a National Research Foundation of Korea grant funded by the Korean government (No. 2019R1F1A1057630 to JYJ).
The data presented in this study are available on request from the corresponding author.
Conceptualization: JYJ
Data curation, Formal analysis: HK, JYJ
Investigation: AJK, HR, JHC, HHL, WC
Methodology, Funding acquisition, Supervision: JYJ
Writing–original draft: HK, JYJ
Writing–review & editing: all authors
All authors read and approved the final manuscript.
Bivariate correlation analysis of serum T50 with (A) albumin, (B) phosphate, (C) calcium, (D) hsCRP, (E) AAC, and (F) BMD total hip. Serum T50 was positively correlated with serum albumin concentration (r = 0.289, p < 0.001) and inversely correlated with serum hsCRP (r = –0.224, p = 0.003) and phosphate (r = –0.156) concentrations.
AAC, abdominal aortic calcification; BMD, bone mineral density; hsCRP, high-sensitivity C-reactive protein.
The mean T-score for BMD measured at the femur neck was relatively lower than that for the BMD assessed at the total hip or lumbar spine (–1.9 ± 1.2, –1.6 ± 1.3, and –1.1 ± 1.8, respectively; p < 0.001). In the multiple comparison test by Tukey method, there were also significant differences between femur neck and lumbar spine (p < 0.001) and between total hip and lumbar spine (p = 0.001), but the difference between femur neck and total hip was not significant (p = 0.27). The thick line within the box represents the median, the upper and lower boundaries of the box represent the interquartile range, the solid square inside the box represents the mean, the upper and lower whiskers represent the maximum and minimum values, respectively, and the gray dots in each group represent individual data.
BMD, bone mineral density.
Baseline characteristics of the study group according to tertiles of serum T50
Characteristic | Total | T50 |
p-value | ||
---|---|---|---|---|---|
T1 | T2 | T3 | |||
No. of patients | 184 | 61 | 62 | 61 | |
T50 (min) | 296.3 ± 85.3 | 204.1 ± 39.0 | 290.9 ± 25.3 | 394.1 ± 40.3 | |
Age (yr) | 61.1 ± 12.3 | 61.8 ± 12.5 | 58.7 ± 13.1 | 62.8 ± 10.9 | 0.65 |
Male sex | 96 (52.2) | 33 (54.1) | 32 (51.6) | 31 (50.8) | 0.93 |
HD duration (mo) | 107 (64–139) | 120 (71–147) | 92 (69–139) | 104 (52–127) | 0.10 |
BMI (kg/cm2) | 23.5 ± 3.8 | 23.1 ± 3.9 | 23.8 ± 3.8 | 23.5 ± 3.8 | 0.56 |
Smoking | 28 (15.2) | 10 (16.4) | 9 (14.5) | 9 (14.8) | 0.95 |
Diabetes mellitus | 87 (47.3) | 25 (41.0) | 29 (46.8) | 33 (54.1) | 0.35 |
Hypertension | 108 (58.7) | 36 (59.0) | 37 (59.7) | 35 (57.4) | 0.97 |
CVD | 75 (40.8) | 27 (44.3) | 21 (33.9) | 27 (44.3) | 0.40 |
spKtV | 1.6 (1.4–1.8) | 1.6 (1.4–1.9) | 1.6 (1.4–1.8) | 1.6 (1.4–1.8) | 0.96 |
RAS blockade | 79 (42.9) | 26 (42.6) | 28 (45.2) | 25 (41.0) | 0.90 |
CCB | 81 (44.0) | 29 (47.5) | 28 (45.2) | 24 (39.3) | 0.64 |
β-blocker | 80 (43.5) | 29 (47.5) | 28 (45.2) | 23 (37.7) | 0.52 |
Phosphate binder | 131 (71.2) | 44 (72.1) | 42 (67.7) | 45 (73.8) | 0.75 |
Statin | 71 (38.6) | 24 (39.3) | 22 (35.5) | 25 (41.0) | 0.81 |
Vitamin D analogues | 123 (66.8) | 41 (67.2) | 37 (59.7) | 45 (73.8) | 0.25 |
Cinacalcet | 17 (9.2) | 8 (13.1) | 5 (8.1) | 4 (6.6) | 0.42 |
Hemoglobin (g/dL) | 10.8 ± 1.3 | 10.7 ± 1.3 | 10.7 ± 1.2 | 11.1 ± 1.2 | 0.07 |
Albumin (g/dL) | 4.0 ± 0.3 | 3.9 ± 0.4 | 4.0 ± 0.3 | 4.1 ± 0.3 | <0.001 |
Cholesterol (mg/dL) | 137.0 ± 34.5 | 128.7 ± 28.6 | 141.9 ± 37.6 | 140.2 ± 35.6 | 0.07 |
Triglyceride (mg/dL) | 101.9 ± 72.7 | 85.4 ± 68.8 | 106.2 ± 74.6 | 113.6 ± 72.8 | 0.03 |
hsCRP (mg/dL) | 0.1 (0.0–0.4) | 0.2 (0.1–0.5) | 0.2 (0.0–0.3) | 0.1 (0.0–0.3) | 0.03 |
Calcium (mg/dL) | 8.2 ± 0.9 | 8.3 ± 0.9 | 8.2 ± 1.0 | 8.2 ± 0.9 | 0.70 |
Phosphate (mg/dL) | 5.3 ± 1.4 | 5.6 ± 1.8 | 5.3 ± 1.3 | 5.0 ± 1.0 | 0.02 |
VD25 (ng/mL) | 17.2 ± 9.8 | 17.4 ± 10.4 | 17.9 ± 10.1 | 16.4 ± 8.9 | 0.61 |
VD1,25 (pg/mL) | 5.9 ± 7.1 | 5.7 ± 7.4 | 5.7 ± 7.0 | 6.4 ± 7.1 | 0.61 |
PTH (pg/mL) | 564.2 ± 380.9 | 649.1 ± 501.2 | 504.2 ± 293.5 | 541.7 ± 306.9 | 0.12 |
ALP (U/L) | 108.5 ± 64.6 | 125.4 ± 95.7 | 98.3 ± 41.2 | 102.0 ± 37.5 | 0.045 |
BMD (g/cm2) | |||||
Lumbar spine | 1.034 ± 0.214 | 0.998 ± 0.218 | 1.045 ± 0.205 | 1.059 ± 0.217 | 0.13 |
Femoral neck | 0.713 ± 0.145 | 0.693 ± 0.159 | 0.729 ± 0.147 | 0.715 ± 0.129 | 0.42 |
Total hip | 0.749 ± 0.164 | 0.717 ± 0.165 | 0.753 ± 0.185 | 0.775 ± 0.135 | 0.06 |
AAC | 4.0 (0.0–12.0) | 4.0 (0.0–10.5) | 3.5 (0.0–8.0) | 5.0 (0.0–11.0) | 0.54 |
Data are expressed as number only, mean ± standard deviation, number (%), or median (interquartile range).
AAC, abdominal aortic calcification; ALP, alkaline phosphatase; BMD, bone mineral density; BMI, body mass index; CCB, calcium channel blocker; CVD, cardiovascular disease; HD, hemodialysis; hsCRP, highly selective C-reactive protein; PTH, parathyroid hormone; RAS, renin-angiotensin-aldosterone; spKtV, single-pool Kt/V; T1, 1st tertile; T2, 2nd tertile; T3, 3rd tertile; VD1,25, 1,25-dihydroxyvitamin D.
Cross-sectional correlation analyses between serum T50 and BMD and other variables
Variable | Age | spKtV | Albumin | hsCRP |
Calcium | Phosphate | PTH | ALP | BMD_LS | BMD_FN | BMD_TH | AAC |
T50 |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Age | 1.000 | ||||||||||||
spKtV | 0.226 |
1.000 | |||||||||||
Albumin | –0.245 |
–0.015 | 1.000 | ||||||||||
hsCRP |
0.025 | –0.120 | –0.205 |
1.000 | |||||||||
Calcium | 0.020 | 0.037 | 0.242 |
–0.107 | 1.000 | ||||||||
Phosphate | –0.350 |
–0.213 |
0.191 |
0.097 | 0.063 | 1.000 | |||||||
PTH | –0.193 |
–0.215 |
0.113 | 0.010 | 0.193 |
0.342 |
1.000 | ||||||
ALP | 0.089 | –0.029 | 0.058 | 0.011 | 0.085 | –0.032 | 0.339 |
1.000 | |||||
BMD_LS | –0.180 |
–0.310 |
0.094 | 0.056 | –0.026 | 0.105 | –0.069 | –0.225 |
1.000 | ||||
BMD_FN | –0.513 |
–0.403 |
0.201* | –0.003 | 0.028 | 0.132 | 0.011 | –0.019 | 0.599 |
1.000 | |||
BMD_TH | –0.353 |
–0.440 |
0.219* | 0.053 | 0.044 | 0.061 | –0.005 | –0.103 | 0.599 |
0.800 |
1.000 | ||
AAC |
0.443 |
–0.009 | –0.126 | 0.089 | 0.063 | –0.051 | –0.072 | 0.126 | 0.024 | –0.267 |
–0.176 |
1.000 | |
T50 | 0.042 | –0.006 | 0.289 |
–0.224 |
–0.005 | –0.156 |
–0.081 | –0.156 |
0.123 | 0.034 | 0.158 |
0.064 | 1.000 |
AAC, abdominal aortic calcification; ALP, alkaline phosphatase; BMD, bone mineral density; FN, femoral neck; hsCRP, highly selective C-reactive protein; LS, lumbar spine; PTH, parathyroid hormone; spKtV, single-pool Kt/V; TH, total hip.
Data for hsCRP and AAC were log-transformed.
p < 0.05.
Linear regression of the association between T50 (every 100 minutes increase) and BMD (g/cm2)
BMD | β (95% confidence interval) | p-value |
---|---|---|
Spine L1–L4 | ||
Crude | 0.03 (–0.01 to 0.07) | 0.10 |
Model 1 | 0.03 (–0.002 to 0.07) | 0.07 |
Model 2 | 0.02 (–0.02 to 0.06) | 0.32 |
Model 3 | 0.02 (–0.02 to 0.06) | 0.33 |
Femur neck | ||
Crude | 0.01 (–0.02 to 0.03) | 0.71 |
Model 1 | 0.01 (–0.01 to 0.03) | 0.42 |
Model 2 | –0.001 (–0.02 to 0.02) | 0.94 |
Model 3 | –0.001 (–0.02 to 0.02) | 0.96 |
Total hip | ||
Crude | 0.03 (0.001 to 0.06) | 0.04 |
Model 1 | 0.03 (0.01 to 0.06) | 0.01 |
Model 2 | 0.02 (–0.01 to 0.04) | 0.19 |
Model 3 | 0.02 (–0.01 to 0.04) | 0.19 |
Model 1: adjusted for age, sex, and smoking. Model 2: model 1 + adjustment for hemodialysis duration (mo), single-pool Kt/V, albumin, and alkaline phosphatase. Model 3: model 2 + adjustment for phosphate binders, vitamin D receptor activators, and cinacalcet.
BMD, bone mineral density.