Age was included in the model irrespective of statistical significance. The variable β-hydroxybutyrate and additional covariates were conditionally selected in a forward stepwise procedure (inclusion criteria P < .05). The nonsignificant variables that were not included in this model using this selection method were body mass index, Hb, hematocrit, erythrocyte, reticulocyte, leukocyte, platelet count, iron, ferritin, transferrin, bilirubin, aspartate aminotransferase, lactate dehydrogenase, haptoglobin, potassium, and group (patients/controls).