Correlation between serum trimethylamine oxide and vascular calcification in patients with chronic kidney disease

Objective  To evaluate the associations between serum level of trimethylamine oxide （TMAO） and vascular calcification and explore the risk factors of vascular calcification in patients with chronic kidney disease （CKD）.

Methods  A total of 118 CKD3-5 patients were assigned into two experimental groups of calcification and non-calcification according to whether or not there was calcification of abdominal aorta. And 60 healthy people with matching age and gender were selected as control group. Serum level of TMAO was determined by enzyme-linked immunosorbent assay （ELISA）. The clinical data of two groups were compared.

Results  TMAO（6.49 ± 0.76）μmol/L, serum phosphorus (1.73±0.62)μmol/L, calcium-phosphorus product(3.66±1.30), parathyroid hormone （PTH）232.90（96.90, 521.60）ng/L, alkaline phosphatase （ALP） 72.00（55.75, 113.50）U/L, serum creatinine （Scr）684.50（511.25, 921.00）μmol/L and C-reactive protein （CRP）5.00（1.28, 21.88）mg/L were higher in experimental group than those in control group （P＜0.05）. Serum calcium（Scr）(2.13±0.24)μmol/L, 25-hydroxyvitamin D23.67（16.84, 30.06）μg/L, albumin （Alb）(37.35±5.97)g/L and estimated glomerular filtration rate （eGFR）6.02（4.70, 8.50）mL·min^-1·（1.73m²）^-1 were lower in control group （P＜0.05）. TMAO(6.01±0.90)μmol/L, age(47.81±13.51)year, proportion of hemodialysis, serum calcium (2.07±0.21)μmol/L and CRP4.70（0.80, 19.44）mg/L were higher in calcification group than that in non-calcification group （P＜0.05）. No statistically significant inter-group difference existed in gender, basic diseases （hypertension & diabetes mellitus）, blood phosphorus, calcium-phosphorus product, PTH, ALP, Alb, total cholesterol （TC）, triglyceride （TG）, 25 hydroxyvitamin D, Scr and eGFR （P＞0.05）. Vascular calcification was correlated positively with age （r = 0.446, P＜0.001）, TMAO （r = 0.614, P＜0.001）, serum calcium （r = 0.192, P = 0.038）, CRP （r = 0.208, P = 0.024） and hemodialysis （r = 0.238, P = 0.009）. Logistic analysis revealed that age （OR = 1.069, 95%CI: 1.025-1.115, P = 0.002） and TMAO （OR = 19.295, 95%CI: 5.785-64.663, P＜0.001） were the independent risk factors for vascular calcification. ROC curve indicated that area under curve （AUC） of TMAO and serum calcium were 0.855 and 0.611 respectively for diagnosing vascular calcification. AUC of combination was 0.868 with a sensitivity of 85.2% and a specificity of 71.9%.

Conclusion  Serum level of TMAO is correlated with vascular calcification in CKD patients. And TMAO is expected to become an adjunct to diagnosing vascular calcification. Due to a low specificity, it should be combined with other risk factors for assessing vascular calcification. The common risk factors for vascular calcification include age, TMAO, serum calcium, CRP and hemodialysis. And age and serum level of TMAO are independent risk factors for vascular calcification in CKD patients.