Establishing national reference values: Blood pressure in Spain

The recently published Consensus for the Control of Hypertension in Spain includes in its final report age-sex specific standards of blood pressure (BP) for Spanish children and adolescents one to eighteen years of age. These BP reference values were obtained by pooling data from fifteen independent cross-sectional studies in children conducted in Spain between 1981-84. The report presents the pooled mean and 90th percentile values of BP for each year of age and sex groups. The process for developing BP standards in Spain was: literature review, selection and reanalysis of qualified studies, pooling of data of independent studies and obtaining national reference values of BP for children and adolescents, and these are all described in this report. The age- and sex-patterns of systolic blood pressure (SBP), and fifth phase diastolic blood pressure (DBP5) in the individual studies and the National Pool are also discussed in detail. Briefly, SBP increased with age in all the individual studies as well as in the National Pool. SBP increased on the average 2.6 mmHg/year in preschool children (1-5 years) and 2 mmHg in boys and girls 6-13 years. Among adolescents (14-18 years) males showed an increase of 1.8 mmHg/year whereas their female counterparts on average reached a plateau by the age of fifteen. The slopes of the SBP curves were similar for boys and girls until the age of fourteen, when separation appeared between the curves for boys and for girls. An increase of DBP5 by age was also observed in all individual studies. Changes in the slope of DBP5 curve by age were also observed in the pool. However, DBP5 increased less sharply than SBP and no separation between boys and girls was observed. The average annual increase for DBP5 both in boys and girls was 1.2 mmHg in all age-groups. Finally, we discuss the appropriateness of pooling data from different studies, their methodologic problems and the limitations in the applicability of specific standards for different populations. Approaches to collecting adequate data for developing reference values for blood pressure and for other cardiovascular risk factors in childhood and the experience of a cooperative group established in Spain for the study of these issues are also discussed in the article.