Association between serum bicarbonate and low mid-upper arm circumference in patients with non-dialysis-dependent...

Although previous experimental studies showed that metabolic acidosis promoted muscle catabolism and impaired protein synthesis, few epidemiological studies reported an independent association between serum bicarbonate levels and muscle atrophy in patients with chronic kidney disease (CKD). We examined the association between serum bicarbonate levels and low mid-upper arm circumference (MUAC), a surrogate marker of low muscle mass, in older adults with non-dialysis-dependent CKD.

A total of 174 patients aged ≥65 years with an estimated glomerular filtration rate <60 ml/min/1.73 m² (33.9% women) were eligible. We cross-sectionally examined the association between serum bicarbonate levels and MUAC using multiple linear regression, adjusting for potential confounders selected by a directed acyclic graph of our causal model. The association between serum bicarbonate and low MUAC was examined by multiple Poisson regression with robust variance. We used two cutoffs to define low serum bicarbonate: serum bicarbonate levels <24 and <22 mmol/L.

Serum bicarbonate levels were positively associated with MUAC (coefficient = 0.158, 95% CI = 0.026-0.289; P = 0.019). Serum bicarbonate levels <24 mmol/L were associated with a higher prevalence of low MUAC (prevalence ratio = 3.50, 95% CI = 1.61-7.61; P = 0.002), whereas the association was attenuated for serum bicarbonate levels <22 mmol/L. Restricted cubic spline analyses suggested a nonlinear association between serum bicarbonate levels and low MUAC.

We found an independent association between serum bicarbonate levels <24 mmol/L and low MUAC, calling for further prospective studies to elucidate the target serum bicarbonate level that would help retard muscle atrophy.