Professionals

Blood pressure centiles come from the quantile spline regression of Rosner and colleagues (Am J Epidemiol 2008;167:653–66), the model that generated the reference tables in the 2017 American Academy of Pediatrics guideline (Flynn et al, Pediatrics 2017;140:e20171904). The model takes exact age and height in centimetres directly, so no interpolation between whole years is needed and no height centile is used as an input. Output agrees with the printed AAP tables to within about 1 mmHg; the printed tables appear to be truncated rather than rounded, which accounts for most of the difference.

The height centile shown is UK-WHO — the WHO 2006 standard to age 4 and UK90 thereafter, as published by the RCPCH. It is reported for context and is not used to compute the blood pressure centiles.

Where a child's height is more than 3.09 SD from the mean for age on the reference population the model was fitted to, no result is returned. This reproduces the behaviour of the original published algorithm, which stops rather than extrapolate.

From age 13 the AAP applies fixed adult thresholds (120, 130/80 and 140/90 mmHg) instead of centiles. Both are shown at every age so the two can be compared.

This tool supports clinical judgement; it does not replace it. Diagnose hypertension on repeated measurements across separate occasions, not a single reading.