Data analysis
REGRESSION
The computer package IBM SPSS Statistics 25 (IBM Corporation, Armonk, NY, USA) was used for statistical analysis. Data are presented as percentages, mean ± SD, geometric mean (SD range), or, in the case of variables which did not conform to a normal or log-normal distribution, median and [inter-quartile range]. For independent samples, two-way comparisons for proportions were by Fisher’s exact test, for normally distributed variables by Student’s To understand the relationship between a low serum bicarbonate and all-cause mortality, (1) unadjusted Cox regression was first performed with low serum bicarbonate as the exposure and all-cause mortality as the outcome (model 1); (2) adjustment was then made for age and sex (model 2); (3) further adjustment was made for those variables independently associated with all-cause mortality but not low serum bicarbonate (model 3); (4) non-significant variables in model 3 were removed using backward conditional modelling (