Purpose: 1) To determine if there are significant differences in laboratory parameters and patient characteristics between patients with low erythrocyte (RBC) folate levels and those with normal RBC folate levels; 2) to determine the correlation between serum and RBC folate levels; 3) to determine if the RBC folate level changed the diagnosis, treatment, and outcome of these patients if the serum folate level was available.
Patients and methods: The study is a retrospective review of all inpatients and outpatients at a public teaching hospital who had an RBC folate level less than or equal to 175 ng/ml (N = 57) over the study period (69 months) and a blindly selected group of patients with RBC folate levels greater than 175 ng/ml (N = 53) during the same period.
Results: Patients with low RBC folate levels had higher mean corpuscular volume (MCV) and red cell distribution width (RDW) values and lower serum folate and B12 values than patients with normal RBC folate levels, but there was no difference in degree of anemia, presence of oval macrocytes and/or hypersegmented neutrophils on the peripheral blood smear, LDH, alcohol use, diet, or any other measured clinical parameter. Serum and RBC folate levels were highly correlated and a low RBC folate affected the clinical outcome of three patients (5% of the low RBC folate group).
Conclusions: Based upon these retrospective data and a review of the literature, we cannot define significant differences between patients with low RBC folate and randomly selected patients with normal RBC folate that could not have been equally well defined using serum folate values. The sensitivity and specificity of a low RBC folate level in the diagnosis of ill or healthy individuals are undefined, and until prospective studies utilizing some of the newer, more specific biochemical indicators of tissue folate are completed, the interpretation of low RBC folate levels will remain problematic.