Validation of a composite scoring scheme in the diagnosis of folate deficiency in a pediatric and adolescent dialysis cohort.

Background: Laboratory indices are often poorly diagnostic of folate deficiency (FD). Compared with iron depletion in hemodialysis (HD) populations, the impact of FD is less appreciated. The composite scoring of hematologic indices of FD may facilitate a prompt and accurate diagnosis, and enhance operational research on folic acid therapy.

Objective: Our objectives were to (1) validate composite scores of folate diagnostic indices, and (2) determine the reliability index of the diagnostic tool.

Methods: A cohort of 30 subjects, with a mean age of 16 (SD +/- 3.2 years), on HD and erythropoietin (EPO) for a minimum of 3 months was studied. After a baseline hematologic assessment, routine folates were administered for 6 months. Composite FD scores (FDS) of baseline mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), random distribution width (RDW), and hemoglobin were determined. Validation and reliability statistics were then analyzed, using the quantitative change in red blood cell folate/plasma homocysteine, or EPO requirement after 6 months of folate use, as diagnostic criteria.

Results: The mean FDS for FD and non-FD subsets were 3.0 +/- 1.3 and 1.4 +/- 0.9, respectively (analysis of variance; P = .0001). The correlation coefficient, r(2), between FD total and FDS was 0.61 (P = .001), and the coefficient between 2 (weekly) values of RDW, MCV, MCH, and MCHC was >0.84 (P = .0001). Scoring tools derived from the first (P = .002) and second (P = .01) halves of the laboratory indices remained discriminatory for the FD and non-FD groups. Baseline serum folate is poorly specific for FD, whereas FD score >or=3 had sensitivity, specificity, and positive and negative predictive values close to 90%.

Conclusions: Composite scoring of erythrocyte indices was predictive of the FD diagnosis, as defined by the quantitative response of red blood cell folate, homocysteine, and EPO dose to folate therapeutic intervention. The diagnostic items yielded a high reliability coefficient. The FDS scheme is a potential tool for the diagnosis and surveillance of FD, particularly in at-risk populations (e.g., dialysis subjects).