Assessment of Folate Status in Obese Patients: Should We Measure Folate in Serum or in Red Blood Cells?

Background Recent studies revealed that obesity is associated with decreased serum but at the same time increased red blood cell (RBC) folate concentrations compared with lean subjects, thus casting doubt upon the agreement between serum and RBC folate measurements for assessing folate status. This work aimed to determine whether these two metrics lead to the same classification of folate status in obese patients. Methods RBC and serum folate concentrations were measured with a chemiluminescent immunoassay in 263 adults with body mass index >= 30 kg/m(2) and without previous bariatric surgery. Among them, 68.1 % were eligible for bariatric surgery. Each serum and RBC folate result was classified as deficient or not according to thresholds recommended by the kit manufacturer (model A) or by the World Health Organization (model B). The agreement between serum and RBC folate results was evaluated using the proportion of overall agreement and the prevalence-adjusted bias-adjusted kappa (PABAK) statistics. Results The overall percentage agreements between serum and RBC measurements were 91.6 % (95 % CI 87.6-94.7 %) and 92.4 % (95 % CI 88.5-95.3 %) with PABAK coefficients of 0.87 (95 % CI 0.82-0.93) and 0.88 (95 % CI 0.83-0.94) in the models A and B, respectively, corresponding to almost perfect agreement. The same was true in the subgroup of patients eligible for bariatric surgery. Gender, age, and BMI did not influence the quality of agreement between the two parameters. Conclusions The present study showed that folate measurements in serum and in RBC display similar performances to assess folate status in obese patients.