Introduction

1. Defining and classifying height in children with cystic fibrosis: comparison of z-score height for age and z-score height for age adjusted for target height Woestenenk, J.W. 1,2; Hoekstra, T. 1; Ent van der, C.K. 2 1 Department of Dietetics and Nutritional Sciences, Julius Centre for Health Sciences and Primary Care, 2 Cystic Fibrosis Centre Utrecht, University Medical Centre Utrecht, The Netherlands Introduction Nutritional status (NS) has a significant effect on survival in patients with Cystic Fibrosis (CF). Height is part of the assessment of NS. In clinical practice, measured height is commonly compared to reference values of healthy children by converting it to z-score height-for-age (HFA). A limitation of this method is that the genetic potential is not taken into consideration. Therefore z-score HFA adjusted for target height (HFA-TH) might be more accurate. The purpose of this study was to compare classification of height expressed as HFA with HFA-TH in Dutch children with CF. Methods In a cohort of 169 Dutch children (90 boys) with CF (age 11.1 ± 3.7 years), height was measured with a stadiometer to the nearest 0.5 cm and expressed as z-score HFA. TH is derived from the average of the two parents' heights, with an adjustment added for boys and subtracted for girls and expressed as z-score. HFA-TH was calculated as HFA z-score TH by subtracting HFA-TH from HFA. A z-score < -2 was classified as malnutrition. Results The classification of height, expressed as z-score HFA and HFA-TH differ in the whole group as well as in the individual patient (figure 1). For the whole group, mean height expressed as z-score HFA and HFA-TH was respectively -0.5 ± 1.0 (2.2 – -2.8) and -1.0 ± -1.0 (1.7 – -3.4). Assessment of the NS according to HFA and HFA-TH showed that respectively 52 (31 %) and 25 (15 %) children had a z-score ≥ 0. According to HFA and HFA-TH respectively, 14 (8 %) and 26 (15%) children were malnourished (table 1). When compared classification of the NS according HFA with HFA-TH we found agreement in 60% (n = 102) of the patients. In 75% (n = 126) of the patients, height expressed as HFA-TH resulted in a more negative z-score, in comparison to HFA. Figure 1: Length of a 10 year old girl with CF. The line represents height expressed as height for age (HFA). The calculated target height is plotted at the right side According to the reference HFA, this girl has a delay in height but is not malnourished. According to height for age adjusted for target height, this child should be classified as malnourished. Table 1: Classification of nutritional status according to height expressed as z-score height for age (HFA) and z-score HFA adjusted for target height (HFA-TH) in 169 Dutch children with Cystic Fibrosis Conclusion Defining height according to HFA and HFA-TH results in a widespread outcome. Therefore, the use of z-score HFA-TH might be helpful to optimize the assessment of the NS in individual patients with CF. Discussion To be able to draw conclusions on which method is the preferred method in clinical practice, longitudinal research of growth needs to be done. Send correspondence to: J.W. Woestenenk University Medical Centre Utrecht Room KH 01.4190 PO Box 85090 3508 GA Utrecht The Netherlands E-mail: J.W. Woestenenk@umcutrecht.nl