WHO height charts can be safely substituted when calculating BP Z-scores in a North American clinic setting

Abstract

Objectives: The Public Health Agency of Canada has officially adopted growth charts from the World Health Organization (WHO); nevertheless, North American blood pressure (BP) Z-scores and percentiles still depend on height Z-scores based on growth charts from the US Centers for Disease Control (CDC), which may differ significantly, particularly in toddlers. Since many practitioners simply replace CDC height scores with WHO equivalents for diagnosing hypertension, we explore the impact of this substitution on BP Z-scores in real-world BPs measured on more than 22,000 children aged 2 to 18 years. Methods: We report agreement between two different measures of the same quantity as Bland-Altman limits of agreement (LOA). Results: In toddlers aged 2 to 5 years, WHO height Z-scores are systematically lower with a bias (mean error) of -0.30 SD, and the 95% LOA range from -0.51 to -0.10 SD. Despite this difference, systolic BP Z-scores were nearly identical (bias = 0.06, LOA = 0.02 to 0.10). For older children and diastolic BP Z-scores, the errors were smaller still, and agreement was equally good for hypotensive, normotensive and hypertensive measurements. Conclusions: Clinicians may safely use WHO height charts when calculating BP Z-scores or percentiles against the National Institute of Health's National Heart, Lung, and Blood Institute reference data.