Average Lifetime Hemoglobin Concentration Improves Prediction of Cognitive Outcomes in Pediatric Patients with Sickle Cell Anemia

Background:Sickle cell anemia (SCA) is associated with cognitive challenges that often worsen as children age. Previous work has established relationships between hematological markers of disease severity (i.e., hemoglobin concentration) and various neurological outcomes, including cognitive impairment. However, most studies have related static, often isolated hemoglobin concentration (Hb) values obtained from a single time-point closest to data collection. Studies of pediatric patients with phenylketonuria and Type I diabetes have demonstrated that longitudinal change and variability in phenylalanine and glucose, respectively, are better indicators of neurological and cognitive outcomes than a single value alone. Our study aimed to be the first study of pediatric patients with SCA to examine the extent to which indices of Hb control (e.g., lifetime average and variability), collected routinely in this patient group, may provide additional prognostic information.

Methods:Data were collected from pediatric patients (aged 4-18 years at enrolment) with and without SCA enrolled on the Sleep Asthma Cohort-III (SAC-III) follow-up study. SAC is a mixed retrospective-prospective study assessing the impact of nocturnal oxygen desaturation on SCA complications. The present investigation assessed participants (see Figure 1 for complete participant demographics) who underwent cognitive evaluation using Wechsler scales measuring domains of IQ, processing speed (i.e., processing speed index [PSI] and Cancellation subtest), and executive function (working memory index [WMI]). Participant demographics and appropriate medical data and history (i.e., hydroxyurea therapy, silent infarction) were obtained via questionnaires and analysis of medical records. Hb (d/L) measures assessed included average lifetime values (i.e., mean and median), variability over the lifetime (i.e., standard deviation), and the single value obtained closest to data collection.

Results:Correlation analyses indicated a strong positive relationship between the mean and median Hb values along with large positive associations between the average and contemporaneous values. Small non-significant correlations were demonstrated between variability and average Hb values (see Figure 1). Initial hierarchical linear regression analyses demonstrated that neither hydroxyurea use nor silent infarct (SCI) status were predictors of any cognitive outcomes or Hb values, so they were not included in any further analyses. Separate regression analyses for each cognitive outcome found that mean lifetime Hb values was the only significant predictor of IQ (p = .04, η ² = .13) and the Cancellation subtest (p = .005, η ² = .22). Mean lifetime Hb values approached significance for PSI (p = .09, η ² = .08), but was not a predictor for WMI (p = .33, η ² = .03).

Conclusion:Our study demonstrated that despite strong correlations between Hb obtained closest to testing and average lifetime values (i.e., rs = .64 and .69), only lifetime Hb predicted cognitive outcomes, particularly processing speed scores from the Cancellation subtest. Variability was not strongly related to other indices of Hb control and did not predict any cognitive outcomes. These results mirror those obtained from other pediatric populations indicating that static, one time values may not best represent clinical manifestations of chronic illness, and the choice of Hb value can differentially influence research study results and clinical prognosis. Future longitudinal work in larger samples is needed, but Hb obtained over the lifetime appears to provide a more precise picture of patients' cognitive developmental trajectory than a single contemporaneous Hb value alone.

Figure 1

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Figure 1

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