PhilSPEN Online Journal of Parenteral and Enteral Nutrition

(Article 10 | POJ_0004.html) Issue January 2010 - January 2012: 75-81

Original Clinical Investigation

The Comparison between percentile and z-score in the BMI based nutrition screening of pediatric patients in the out-patient department of the Institute of Pediatrics in St.Lukes Medical Center, Quezon City, Metro-Manila, Philippines

Abstract | Introduction | Methodology | Results | Discussion | Conclusion | References | Back to Total Names Codes

Submitted: September 10, 2010 | Posted January 21, 2011

Authors:

Edna P. Llido MD, FPPS (1), Cynthia Aquino MD, FPPS (1), Mary Anne B. Santos MD, DPBCN (1,2), Luisito O. Llido MD, DPBCN (1,2)

Institution where research was conducted:

  1. Pediatric Out Patient Department Group, Institute of Pediatrics, St. Luke’s Medical Center, Quezon City, Metro Manila, Philippines
  2. Clinical Nutrition Service, St. Luke’s Medical Center, Quezon City, Metro Manila, Philippines

 

ABSTRACT: | Back

Background: BMI based nutrition screening is easy to use for pediatric patients, but it has two reference standards: the percentile and the z-score. There are calls to decide which of these should be used in the pediatric Out-Patient and Hospitalized patients.

Objective: To determine which reference to use in the BMI based nutrition screening of pediatric patients: percentile versus z-score.

Methodology: All pediatric patients in the OPD were nutritionally screened using the WHO 2006 to 2007 BMI standards from February to June 2011. Anthropometric data taken were heights in kg and weights in meter using calibrated instruments supervised by a clinical dietitian. A software was designed to determine the percentiles and z-score and the data was saved in the computer database. Differences were compared using T-Test or Wilcoxon signed rank test.

Results: A total of 1,766 patients were included in the study with a male to female ratio of 1.04 to 1. There was no difference between percentile and z-score in the following categories: normal BMI (83%), overweight BMI (7.6%), and obese BMI (2.7%). A difference was seen in the underweight BMI category (percentile = 7.4% vs. z-score = 6.7%, p < 0.05, T-Test) and this was noted to be due to an additional classification of severe underweight in the z-score standard.

Conclusion: There is no difference in the results of BMI based nutrition screening using either z-score or percentile for normal, overweight, and obese nutritional status in pediatric patients except for the underweight due to an additional classification of severe underweight in the z-score category.
 
KEYWORDS: BMI, percentile, Z score, pediatric, nutrition screening, Philippines

INTRODUCTION | Back

Nutrition screening of pediatric patients is part of the over-all care of pediatric patients both in the out-patient and in-patient setting. Since it was established that nutritional status and growth patterns differ between ages and sex from the normal to the extremes of body composition like underweight or obese, standards of growth and development were developed to serve as guides for declaring a pediatric patient as “normal” or “abnormal” in either growth or stature. The normal curves developed by National Center for Health Statistics and Center for Disease Control (CDC) [1] from the United States and from the World Health Organization (WHO) [2] were adapted for use in the Philippines and nutrition agencies of the Philippines like the Food and Nutrition Research Institute (FNRI) together with the Philippine Pediatric Society which made initiatives to develop curves and reference values from the local pediatric population [3]. The FNRI standards were then born and after a few more years the International Reference Standards (IRS) [4] were developed to serve as updates from the FNRI standards. The use of all four were found to be confusing so the Pediatric Department of St. Luke’s Medical Center made a study to determine which of these four reference standards could be used. [5] It was seen that the WHO-MGRS [6] and CDC growth standards came closest to depicting the normal growth curve distribution pattern, therefore, the current WHO 2006-7 [7] is now used by the institution for its nutrition screening and nutritional assessment functions. The WHO standards were chosen over the CDC since it covered the normal population and the age range covered was from 0 to 18 years old.

One more issue raised by the pediatricians was: most of them are using the BMI percentile values and there are calls from some sectors to adopt the BMI z-score as the standard to follow. In order to resolve this issue another study was designed to compare the difference(s), if there was any, between the BMI percentiles and the z-score of the WHO 2006-7 growth standards. The objectives of the study are: a) To validate the nutritional status values based on the World Health Organization (WHO) Body Mass Index (BMI) nutritional status charts on pediatric patients of the SLMC Institute of Pediatrics; b) To compare the z-score and percentile cut off results for nutritional status from the pediatric patients of the SLMC Institute of Pediatrics; and c )To decide which criteria to use for the nutrition screening of pediatric patients.

METHODOLOGY | Back

The nutrition screening tool for evaluation is the WHO BMI based nutritional status form modified for use for the Institute of Pediatrics of St. Luke’s Medical Center (Figures 1 and 2). The Inclusion criteria are: all pediatric patients seen at the Out Patient Department of St. Luke’s Medical Center. In order to facilitate the data gathering process, a computer program was developed for both database and computation purposes. These are the data gathered: patient identification (Last Name, First Name, Middle Name), age, sex, height in meters, and weight in kilograms, and Body Mass Index (BMI). The anthropometric measurements and other data were taken by pediatric residents and consultants with rotating assignments at the Out-Patient Department of the Institute of Pediatrics. The weight was taken from DETECTO (Webb City, Missouri) stand weighing scale with height measuring bar and infant weighing scale and length measuring mat by SECA (Hangzhou, China).

ped_bmi tbl10

Table 1: Comparison between z-score and percentile

bmi nutisrn

Figure 1: Pediatric BMI based Nutrition Screening Form for Boys; Note the integrated curves of both BMI percentiles and Z-score

bmi nutrsrc girls

Figure 2: Pediatric BMI based Nutrition Screening Form for Girls

The standard procedures followed were: a) Height in meter(s) and weight in kilogram(s) were taken from the patients based on correct methods of taking height and weight of pediatric patients as adopted by the nursing department on correct nursing procedures; b) Height in meters and weight in kilograms from which the BMI and z-score are automatically computed by the computer program are taken and encoded; c) the number of patients within all categories are summed up and the difference between all groups are determined.

These are the outcomes assessed: a) Percentage of normal, underweight, severe underweight, overweight and obese in the Filipino pediatric population seen in the OPD of SLMC based on the WHO BMI classification, b) Presence or absence of differences in the number of patients included in the different cut-offs of either z-score or percentiles, classified as severe underweight, underweight, normal, overweight, and obese are determined using paired T-Test or Wilcoxon Signed Rank Test. [8]between all groups are determined.

These are the outcomes assessed: a) Percentage of normal, underweight, severe underweight, overweight and obese in the Filipino pediatric population seen in the OPD of SLMC based on the WHO BMI classification, b) Presence or absence of differences in the number of patients included in the different cut-offs of either z-score or percentiles, classified as severe underweight, underweight, normal, overweight, and obese are determined using paired T-Test or Wilcoxon Signed Rank Test. [8]

RESULTS | Back

Patient profile: There was a total of 1,766 out-patient pediatric patients included in the study with the male to female ratio at 1.04 to 1. Most of these patients were either well-baby follow ups or regular check-ups at the outpatient clinic.
Nutritional status based on the BMI percentile standards compared to the BMI z-score standards show the following (Table 1):

  1. Normal: a total of 1,453 patients or 82.3% were found to have normal BMI percentiles or z-scores and no difference was found between these two standards.
  2. Underweight: there was a significant difference between underweight standards (BMI percentile = 131 or 7.4%; BMI z-score = 119 or 6.7%). However when the underweight and severe underweight in the BMI z-score were combined, there was no difference in both groups (percentile versus z-score).
  3. Overweight: a total of 135 or 7.6% patients were found to have overweight BMI percentiles or z-scores and no difference was found between these two standards.
  4. Obese: a total of 48 patients or 2.7% were found to have obese BMI percentiles or z-scores and no difference was found between these two standards.

DISCUSSION: | Back

It is shown in this study that using the BMI percentile or BMI z-score would yield similar results thus either of these two standards can be used for the nutrition screening of pediatric patients. The significant result for the underweight classification (a difference between BMI percentile [131 or 7.4%] and BMI z-score [119 or 6.7%], p<0.05, Wilcoxon Signed Rank Test, table 2) was due to the additional classification of severe underweight in the BMI z-score standards (below -3) which was not present in the BMI percentile classification. However when the underweight and severe underweight in the BMI z-score were combined only as “underweight”, no difference was noted between both groups.

An advantage of using the BMI z-score would be in the determination of severely underweight patients, which classification was not included in the BMI percentile cut-off values. Another advantage was earlier cited by some pediatricians who pointed out that most of the reported BMI values presented in the literature were in the form of z-score. In the overall scheme of things if the goal is merely to determine the nutritional status of a pediatric patient as normal, underweight, overweight, or obese then either the BMI percentile or the BMI z-score can be used. The forms for nutrition screening used in this study (Figures 1 and 2) are thus acceptable for use either in the hospital or community set-up. The results of this study is in full accord with reports from other countries on the use of the WHO 2006-7 BMI based child growth standards (Canada [9], United States [10], United Kingdom [11], Eastern Mediterranean [12], and Middle East [13]).

CONCLUSION: | Back

There is no difference in the results of nutrition screening using either z-score or percentile for normal, overweight, and obese. There is a difference in the underweight class due to an additional classification (severe underweight) in the z-score group, however, if these were combined no difference in number between percentile and z-score is noted.
Therefore either of these criteria (percentile or z-score) can be used in the nutrition screening of pediatric patients.

REFERENCES: | Back

  1. National Center for Health Statistics in collaboration with the National Center for Chronic Disease Prevention and Health Promotion (2000). http://www.cdc.gov/growthcharts.
  2. World Health Organization. Physical status: The use and interpretation of anthropometry. Geneva, Switzerland: World Health Organization 1995. WHO Technical Report Series.
  3. Florentino RF, Santos-Ocampo P, et al. FNRI-PPS Anthropometric tables and charts for Filipino children. Manila: Food and Nutrition Research Institute, DOST and Philippine Pediatric Society, 1999.
  4. Mendoza TS and Barba C. A Handbook on International References Standards (IRS) growth tables and charts adopted for use in the Philippines. Food and Nutrition Research Institute, DOST and UNICEF, 2003.
  5. Llido EP, Macalintal MM, Reyes MCS, Gundao ND, Santos MB, Navarrete DI. Comparison of standard values of nutrition screening and assessment using BMI percentiles from FNRI-PPS, IRS, CDC 2000, and WHO-MGRS child growth standards in the pediatric population of a tertiary care hospital in the Philippines admitted between years 2000 and 2003; available at: http://www.philspenonline.com.ph/Phil_PedStds_compare_slmc.pdf. Accessed August 15, 2011.
  6. De Onis M, Garza C, Victora CG, Bhan MK, and Norum KR. The WHO Multicentre Growth Reference Study (MGRS): Rationale, planning, and implementation. Food and Nutrition Bulletin 2004; 25 (supplement 1): S3-S84.
  7. The WHO Child Growth Standards. 2006; available from: http://www.who.int/childgrowth/standards/en/index.html. Accessed August 16, 2011.
  8. Dawson B and Trapp RG, Basic and clinical biostatistics. 3rd ed. Lange Medical Books/ McGraw-Hill, 2001.
  9. Dietitians of Canada; Canadian Paediatric Society; College of Family Physicians of Canada; Community Health Nurses Association of Canada. The use of growth charts for assessing and monitoring growth in Canadian infants and children. Can J Diet Pract Res 2004; 65(1): 22-32.
  10. Grummer-Strawn LM, Reinold C, Krebs NF. Use of World Health Organization and CDC Growth Charts for Children Aged 0–59 Months in the United States. MMWR Sept 2010; 59(RR9). Available at http://www.cdc.gov/mmwr/pdf/rr/rr5909.pdf.  Accessed August 12, 2011.
  11. Wright CM, Booth IW, Buckler JMH, Cameron N, Cole TJ, Healy MJR, et al. Growth reference charts for use in the United Kingdom. Arch Dis Child 2002; 86: 11-14.
  12. Abul-Fadl A, Bagchi K, Cheikh Ismail L. Practices in child growth monitoring in the countries of the Eastern Mediterranean Region. East Mediterr Health J. 2010;16(2): 194-201.
  13. Bener A, Kamal AA. Growth patterns of Qatari school children and adolescents aged 6-18 years. J Health Popul Nutr. 2005; 23(3): 250-8.

Abstract | Introduction | Methodology | Results | Discussion | References | Back to Total Names Codes