Table 3.

Threshold Effect Analysis of Serum Folate on Mortality Using Piece-Wise Linear Regression Model

Model	HR (95% CI), p
Linear analysis model	1.01 (1.00, 1.02) 0.0195
Two-piece-wise regression model
Inflection point of serum folate (ng/mL)	14.8
< Inflection point	0.94 (0.89, 0.99) 0.0236
> Inflection point	1.01 (1.01, 1.02) 0.0004
Likelihood ratio test	0.009

Notes: To assess threshold effect and estimate the risk of death associated with folate concentration, we dichotomized serum folate using the cutoff of 14.8ng/mL. The adjusted variances included in the Cox model were as following: age, sex, race, hypertension, physical activity, body mass index, eGFR, serum vitamin B12, albumin, serum glucose, phosphorus, uric acid, total iron binding capacity, folate as dietary folate equivalents, food folate.

Abbreviations: ACRs, urinary albumin-creatinine ratios; BMI, body mass index; CI, confidence interval; CKD, chronic kidney disease; eGFR, estimated glomerular filtration rate; HR, hazard ratio; IRB, Institutional Review Board; MDRD, Modification of Diet in Renal Disease Study equation; NCHS, National Center for Health Statistics; NDI, National Death Index; NHANES, National Health and Nutrition Examination Survey; TIBC, total iron binding capacity.