ASSESSMENT OF NUTRITIONAL STATUS

Learning objectives Value the use of nutritional diagnosis in clinic and at the level of population. Understand the implications for using nutritional indices. Define anthropometry. List 10 nutritional indices. List the requirements for measuring anthropometric data. List two references used for anthropometric indices. Understand the implications of international references for assessment of local people.

Learning objectives Compare the interpretation of single Vs multiple serial measurements of indices. List the data needed for calculation of nutritional indices. Identify a computer program used for calculating nutritional indices. Learn the formula for calculating z score. Identify the cut-off values for percentiles and z- score used for defining malnutrition and obesity. Differentiate between acute and chronic malnutrition.

INTRODUCTION The nutritional status is influenced by food intake, quantity & quality, & physical health. Malnutrition Obesity

Nutritional Assessment Why? The purpose of nutritional assessment is to: Identify individuals or population groups at risk of becoming malnourished. Identify individuals or population groups who are malnourished

Nutritional Assessment Implications? To develop health care programs that meet the community needs which are defined by the assessment To measure the effectiveness of the nutritional programs & intervention once initiated

Anthropometric Methods (Definition) Anthropometry is the measurement of body height, weight & proportions. It is an essential component of clinical examination of infants, children & pregnant women.

Nutritional indices Weight for age Height for age Weight for height BMI BMI for age Mid-arm circumference for age Mid-arm circumference for height Skin fold thickness Head circumference Waist / hip ratio

Anthropometry for children Growth assessment is an essential component of pediatric medicine. The most powerful tool in growth assessment in children is the growth chart. It requires: Accurate scale A measuring board (stadiometer). For infants, the measure of linear growth is length, taken by two examiners (one to position the child) with the child supine on a measuring board. For older children, the measure is stature, taken with a child standing on a stadiometer A tape measure. Growth assessment is an essential component of pediatric health surveillance because almost any problem within the physiologic, interpersonal, and social domains can adversely affect growth. The most powerful tool in growth assessment is the growth chart.

Reference values The old version of standard growth charts were based on data collected by the National Center for Health Statistics, 1977 (NCHS). These normalized growth curves are recommended by the World Health Organization (WHO) for international use. Newer standards are being used, based on a nationally representative sample collected from 1988 to 1994 as part of the US National Health Examination (NHES) and National Health and Nutrition Examination Surveys (NHANES-III) data. Published by CDC in year 2000. Although this population is dissimilar to much of the rest of the world, the NCHS charts have been accepted by the World Health Organization as the international standard of growth for the first 5 yr of life.

Why to accept the international standards as reference in Iraq Disparities in growth between developed and developing countries reflect nutritional rather than genetic differences. Remember: The NCHS curves are less appropriate for adolescents. Growth during adolescence is linked temporally to the onset of puberty, which varies widely across populations.

How many measurements do we need? Ideally, individuals should have several anthropometric measurements over time.  A decline in an individual's anthropometric index from one point in time to another could be an indication of illness and/or nutritional deficiency that may result in serious health outcomes. A single set of measurements may be used for screening populations or individuals to identify abnormal nutritional status and priority for treatment. Anthropometry can be used to assess nutritional status at both the individual and the population level. Growth is a process rather than a static quality. An infant at the 3rd percentile of weight for age may be growing normally, may be failing to grow, or may be recovering from growth failure, depending on the trajectory of the growth curve. Typically, infants and children stay within one or two growth channels. This canalization attests to the robust control that genes exert over body size. The analysis of growth patterns provides critical information for the diagnosis of failure to thrive (FTT). There is no universally agreed-on criterion for FTT or growth failure; most consider the diagnosis if a child's weight is below the 3rd percentile or drops down more than two major percentile lines.

Data needed for calculation? Information is needed on each individual's: Sex age (in months for under 5 years of age) Weight (Kg) Height (cm) head circumference (cm) arm circumference (cm) From these data it is possible to form different  indices, including those that relate to height-for-age (HA), weight-for-age (WA), weight-for-height (WH), head circumference -for-age (HCA), body mass index-for-age (BMIA), mid upper arm circumference-for-age (MUACA) and mid upper arm circumference-for-height (MUACH).  

Calculation? Separate charts are provided for boys and girls. These indices can be expressed in terms of Z- scores or percentiles. 𝑍= 𝑉𝑎𝑙𝑢𝑒 −𝑀𝑒𝑎𝑛 𝑜𝑓 𝑟𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒 𝑆𝐷 𝑜𝑓 𝑟𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒 The reference group is defined by gender and age group. Epi-info is a CDC published computer software that can calculate nutritional indices From these data it is possible to form different  indices, including those that relate to height-for-age (HA), weight-for-age (WA), weight-for-height (WH), head circumference -for-age (HCA), body mass index-for-age (BMIA), mid upper arm circumference-for-age (MUACA) and mid upper arm circumference-for-height (MUACH). Remember from your biostatistics course that 95% confidence interval which contain what we refer to as normal values is equal to (mean + / - 1,96 SD), this translates in percentiles to 3rd and 97th centile (it should be 2.5th and 97.5th centile, but it is easier to remember the 3rd and 97th centile). The proportion of the population that falls below a Z-score of -2 is generally compared with the reference population in which 2.3% fall below this cutoff. Z-scores are useful because they have the statistical property of being normally distributed, thus allowing a meaningful average and standard deviation for a population to be calculated.  It is frequently used in research and recommended by WHO. Percentiles are useful because they are easy to interpret (e.g., in the reference population 3% of the population falls below the 3rd percentile). Percentiles are more easily understand by doctors, therefore they are used in growth charts, while z-scores are more useful in research, because of their statistical properties

BMI for age percentiles curve (Boys)

Interpretation of indices Weight-for-height (or BMI for age) below the fifth (or third) percentile is the single best growth chart indicator of acute malnutrition. While between 85th and 95th centile is labeled as overweight. Above the 95th or 97th centile is obese. Low weight-for-height or BMI-for-age is considered an indicator of acute under-nutrition (thinness or wasting) and is generally associated with failure to gain weight or a loss of weight. Low height-for-age is considered an indicator of chronic under-nutrition (shortness or stunting), BMI-for-age is also used to assess overweight and at risk for overweight.   Weight-for-age is primarily a composite of weight-for-height and height-for-age, and fails to distinguish tall, thin children from short, well-proportioned children.

Interpretation of indices After several months of caloric deprivation, the height- for-age curve drops (stunting or chronic malnutrition). The weight-for-age is a composite indicator, which can not differentiate acute from chronic malnutrition. It is the best screening tool. Weight for age below 2 SD from median or mean (-2 Z) is regarded as Malnutrition. It is used for mass screening of children to detect under nutrition. While a Z score of +2 and above is an indication of obesity. The cutoff for very low anthropometric index (severe malnutrition) is usually Z ≤ -3 Z-scores, also referred to as standard deviation (SD) units, are frequently used.  The Z- score in the reference population has a normal distribution with a mean of zero and standard deviation of 1.  For example, if a study population has a mean WHZ of 0, this would indicate that it has the same median WH as the reference population.

Nutritional Indices in Adults The international standard for assessing body size in adults is the body mass index (BMI). BMI = Weight (kg) / Height (m²) Evidence shows that high BMI (obesity level) is associated with type 2 diabetes & high risk of cardiovascular morbidity & mortality

BMI (WHO - Classification) BMI < 18.5 = Under Weight BMI 18.5-24.5 = Healthy weight range BMI 25-30 = Overweight (grade-1 obesity) BMI > 30-40 = Obese (grade 2 obesity) BMI > 40 = Very obese (morbid obesity)

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