Participants were predominantly white and highly educated and had a mean age of 73.9 ± 2.8 (). The majority of participants had 12 or more years of formal education, lived alone, and had never smoked. More than 80% of participants had a MMSE score of 27 or greater. The vast majority of participants had Hb in the normal range according to the WHO criterion, with only 8.6% (n = 30) with Hb less than 12.0 g/dL. Participants had good physical functioning, with more than half rating their health status as excellent or very good and less than 7% reporting difficulty performing IADLs.
Better TMT-B performance was positively associated with younger age, white race, more years of education, higher Hb, fewer depressive symptoms, better pulmonary function, better self-perceived health status, and faster 1-m usual walking speed (). No statistically significant associations (P > .05) were found in bivariate analysis between TMT-B performance and the following variables: smoking status, hypertension, stroke, diabetes mellitus, cancer, calculated creatinine clearance, BMI, total cholesterol, TSH, IL-6, and drinking habit. Approximately 10% of WHAS II subjects were not included in this analysis because of missing TMT-B or Hb. Those not included were more likely to be African American and have less education than those in the analytic sample but did not vary according to the other characteristics presented in .
displays the observed relationship between Hb and TMT-B, TMT-B – TMT-A, and TMT-A scores. The percentage of subjects in the best TMT-B performance tertile was lowest for levels of Hb within the range of 10.0 to 11.9 g/dL, intermediate for Hb within the range of 12.0 to 12.9 g/dL, and highest for the categories including Hb concentrations of 13 g/dL or greater (). Conversely, having Hb within the range of 13.0 to 13.9 g/dL was associated with the lowest percentage of participants in the worst TMT-B performance group. The number of participants with Hb of 15.0 g/dL or greater was small (n = 21). There was strong statistical evidence against the null hypothesis of TMT-B performance homogeneity across the different Hb categories (i.e., chi-square test of 24.6 with 8 degrees of freedom, P= .04. Consistent with what was observed between Hb and TMT-B, the percentage of those in the best tertile of the TMT-A and TMT-B – TMT-A measures was lowest within the Hb range of 10.0 to 11.9 g/dL ().
Figure 1 Distribution of study subjects according to hemoglobin categories and performance on tests of executive function. Indicated is the percentage of subjects in each performance group (based on distribution tertiles) as measured using the (A) Trail Making (more ...)
shows the results of polytomous logistic regression models estimating the likelihood of being in the worst (top) rather than the best (bottom) or intermediate tertile of TMT-B, TMT-B – TMT-A, and TMT-A performance “independently” associated with presence of WHO-defined anemia. For example, the likelihood of being in the worst, as opposed to being in the best, TMT-B tertile was more than five times as high (odds ratio (OR) = 5.2, 95% confidence interval (CI) = 1.3–20.5) for subjects with anemia as for those without anemia after controlling for major potential confounders such as age, education, CVD, renal function, and other major indices of disease, disease severity, and physiological impairment. Similar analysis conducted after excluding the 15 subjects for whom TMT-B performance data were imputed led to analogous results (data not shown). Consistent results were obtained for the relationship between anemia and decline in TMT-B – TMT-A and TMT-A performance.
Multivariate Polytomous Logistic Regression Estimates of the Likelihood of Being in the Worst or Intermediate (Rather than in the Best) Tertiles of Trail-Making Test (TMT)-B, TMT-A, and TMT-B–TMT-A Performance Linked to Prevalent Anemia)
Additional polytomous logistic regression analysis was done to further quantify the increase in the percentage of subjects in the worst tertile of TMT-B across the first three Hb categories observed in . In this analysis, given the similar distribution of TMT-B performance across Hb levels of 13.0 to 13.9 g/dL, 14.0 to 14.9 g/dL, and 15.0 g/dL or more, these Hb categories were grouped together. Using this approach, the fully adjusted odds of being in the worst as opposed to in the best TMT-B tertile were 4.9 (95% CI = 1.2–19.7) and 5.9 (95% CI = 1.3–26.4) times as great for subjects with Hb levels of 12.0 to 12.9 g/dL and less than 12 g/dL, respectively, as for those with Hb of 13.0 g/dL or greater (data not shown).