Nutritional Assessment

Instructional Objectives

By the end of this lesson, the students would be able to:

•Define what NA is

•Identify and name the major types of NA methods,

•Identify the factors influencing the NS,

•Distinguish the nutritional indices used in children & adult,

•Expected to apply the basics of anthropometrics measurement,

•Discuss the pros and cons of the major NA methods,

•Learn the various clinical symptoms/ signs helpful in NA

Definitions• Refers to the interpretation of information

obtained from anthropometric, dietary, biochemical, clinical signs/symptoms and socio-demographic information.

What does good NS mean?

• Good status of health;

• Good supply of energy to perform daily activities;

• Good cognitive and analytic skills;

• Speedy healing process of injuries & recovery from illness.

Factors influencing NS

History• Nutritional Assessment….used in

– Schools: to identify those who need supplementary feeding

– Military: to identify those ‘fit’ from the ‘unfit’

– Insurance purposes

– Now used in community and clinical settings

Forms of Nutritional Assessment :

1. Surveys(a cross-sectional asst of nutritional status of a selected

population group)2. Surveillance(Continuous monitoring of the nutnal status of selected popun

groups)

3. Screening(Identification of malnourished individuals requiring intervention)

N.B: each of the above has been adopted in clinical medicine as well as preventive medicine

1. Nutrition Survey

Uses:• Establish baseline nutritional data • Ascertain overall nutritional status of the population• Identify population ‘at-risk’ to chronic nutritional• To make fair allocation of resources to those in need• To formulate nutrition-related policies

Limitations:• Less likely to identify acute malnutrition• Not suitable to study causes of malnutrition

2. Nutritional surveillance

Uses:– Identify possible causes of malnutrition– Help to formulate and initiate interventions at

population or sub-popn level– Formulate predictions based on current trends

Note: NS carried out on selected individuals is called ‘Monitoring’

3. Nutrition screening

• Identification of malnourished individuals requiring intervention

• Involves a comparison of individual’s measurements with predetermined risk levels or ‘cut-off’ points

• Can be done at individual or popn level

• Often less comprehensive than surveys or surveillance studies

Nutritional Assessment Methods

A. Anthropometric

B. Biochemical/Laboratory

C. Clinical

D. Dietary

E. Economic/other methods

N.B: The ABOVE methods can be used either alone or more effectively in combination

DIETARY METHODS(11 DIFFERENT METHODS)

1. Dietary methods

Identifies the first stage of nutritional deficiency;

The nutritional deficiency could be: • Primary (low levels in the diet) or

• Secondary (interference with absorption, transport, utilization, or excretion of nutrients because of some drugs, dietary components, or disease states)

Detailed dietary HistoryInterview method consisting of: •24hr recall of actual intake• information on overall usual eating pattern and,•food frequency questionnaire

Used to assess USUAL food &/ nutrient intakes over a relatively long time period (estimate prevalence of inadequate intakes)

Food Frequency Questionnaire

Uses comprehensive list of specific food items to record intakes over a given period (day, wk, mo, yr)

Designed to obtain qualitative data on USUAL intakes of foods over a long time period

Commonly used Dietary methods

Twenty-four-hour Recall

Recalls food intake in the last 24hr by the subjects in an interview (household/individual)

Useful for assessing usual intakes of a large population

Used for international comparison of relationship of nutrient intakes to health

Weighed or measured Food intakeAll foods & beverages consumed will be weighed (usually for a week)

Used to assess accurate intakes of individuals

Dietary methods ...

Limitations

Advantages

• Relatively cheaper & quick • Less respondent burden• Gives the dietary habits of

individual/group s over a longer periods of time

• Targets the dietary questions to specific dietary habits/intake of specific interest

• Less costly when self administered

Disadvantages

• Respondent memory lapse

• Social desirability bias Has less precision

• Accuracy depends on the respondent’s ability to estimate portion sizes

• Difficult to validate• Difficult where

different staple foods are consumed

Biochemical methods

2.Biochemical methods

• In primary and/or secondary deficiencies, the tissue stores become gradually depleted.

• This may result in reductions in the levels of nutrients or their metabolic products in certain body fluids and tissues, and/or in the activity of some nutrient-dependent enzymes.

• Biochemical and/or physiological/behavioural function tests could detect these states

(a)static: detected by body fluids (invasive) Examples: Hb, UIE, Serum retinol, Albumin etc(b) functional: detected by abnormal test results

Examples of functional test:– Dark adaptation test (VAD)– Taste acuity (Zinc)– Capillary fragility (Vit C)– Cognitive function (iron)

Functional tests provide a measure of the biological importance of a given nutrient b/c they assess the functional consequences of the nutritional deficiency

Types of Biochemical Methods

Advantages and disadvantages of Biochemical methods

Advantage

• It is more objective• Detects deficiency• Provides gradable

Information

Disadvantages

• Ideal biological material may not be accessible for routine use

• May not reflect presence of pathological lesions

• Expensive & Invasive procedures

• Needs skilled staff, equipment &  Has quality control problems during sample collection & analysis

Clinical methods

3. Clinical methods• A medical history and physical examination are

used to detect symptoms and signs;

• These Sx and Sn are often non-specific and only develop during the advanced stages of nutritional depletion;

• Table 1 summarizes the major clinical findings of clinical importance.

Table 1: Summary of clinical methods

Sign/symptoms

• Night blindness, Bitot’s spots• Easy bruising of skin, Spongy

bleeding gums• Edema , short stature• Pallor, easy fatigability ,

anorexia, shortness of breath

• Dental carries , dental cavities

 • Fluoride excess

Nutritional abnormality

• Xerophthalmia• Scurvy • Protein deficiency• Deficiency of Iron,

Vitamin B12,Folic acid, copper

• Fluoride deficiency or increased consumption of CHO

• Dental staining, fragility of bone, teeth

Anthropometric methods

4. Anthropometric methods

• Measurements of the physical dimensions and gross composition of the body – vary with age and degree of nutrition

• Particularly useful when chronic imbalances of protein and energy are likely

• Provides information about past nutritional history

Anthropometry - Advantages• Simple, safe, non-invasive

• Equipment is inexpensive, portable, & durable

• Needs less skill

• Precise and accurate

• Info is obtained on past nutnal history which cannot be obtained with equal confidence using other techniques

• Can be used to evaluate changes in nutritional status overtime (secular trend)

• Can serve as a screening test

Anthropometry-Limitations

• Relatively insensitive and can’t detect changes in nutritional status over short periods of time

• Can’t identify specific nutrient deficiencies (e.g. stunting from Zn deficiency Vs PEM)

5. Other MethodsNutritional assessment may also involve collection of other variables known to affect nutritional status of a population

• Socio-demographic data (birth order, marriage breakdown, death of either parent…)

• Cultural practices, food habits• Economic and agricultural (Food prices, info on

marketing, distribution, & storage of food)• Health and vital statistics (Coverage of safe water,

Immunization coverage, Low birth weight rate, Exclusive breast feeding rate, Age and cause-specific mortality rates, etc)

Anthropometric Assessment

Two types:

• Growth• Height/length• Body weight• Head circumference

• Body composition• Body fat• Fat-free mass

– Skeletal & non-skeletal muscle– Soft lean tissues– Skeleton

Body Composition

Fat Mass– Skin-fold thickness

• Triceps, biceps, subscapular, suprailiac, & midaxillary skin folds

Body composition (fat mass)• Waist-hip ratio

Female Male

Body composition cont…

Fat-free mass• Mid-upper-arm-circumference• Mid-upper-arm muscle circumference• Mid-upper-arm muscle area

Evaluation of Nutritional Assessment Indices

• Indicator

• Indices

• Cut-offs

• Trigger level

Evaluation of Nutritional Indices• NI can be evaluated by comparison with a distribution

of reference values, or with reference limits drawn from the reference distribution

• Reference values are obtained from a healthy reference sample group

• The distribution of these reference values forms the reference distribution

• In population studies, the distribution of the observed values can be compared using percentiles, and/or standard deviation scores derived from the reference data

Evaluation of Nutritional Indices cont….

Cut-off points:• Are based on the relationship between NI and

functional impairment and/or clinical signs of deficiency.

• The choice of a cut-off to differentiate between malnourished and well-nourished states for a particular index affects both the sensitivity and specificity.

• There is always misclassification because of biological variation among individuals.

Evaluation of Nutritional Indices cont….

• For example when the cut-off for MUAC (mid-upper-arm-circumference) is reduced from <14cm to <12.5cm, the specificity in predicting malnutrition (based on WFH < 60% of median) increases from 82.7% to 98%, whereas the sensitivity falls from 90.4% to 55.8%.

Nutritional Status Distribution of Population

Evaluation of Anthropometric indices cont...

• The selection of appropriate reference data to establish ‘risk’ categories is a difficult problem.

• Some investigators advocate the use of local reference data derived from ethnically similar but privileged groups living in same country, while others suggest the opposite.

• The WHO recommends the US National Center for Health Statistics (NCHS) growth percentiles as an international reference.

The WHO (NCHS) reference standards

• The reference population chosen by NCHS was a statistically valid random population of healthy infants and children.

• Available evidence suggests that until the age of 10 years, children from wellnourished and healthy families throughout the world grow at approximately the same rate and attain the same height and weight as children from industrialized countries.

The WHO (NCHS) reference standards

• The NCHS/WHO reference standards are available for children up to 18 years old but are most accurate when limited to use with children up to the age of 10 years.

Evaluation of Anthropometric indices…

• Cut-off points are often established by reviewing anthropometric characteristics of individuals with clinically moderate and/or severe malnutn or who subsequently die.

• In population studies, cut-off points may be combined with ‘trigger levels’ to define criteria for intervention.

• For eg. An intervention may be initiated if at least 10% of the population have a specific anthropometric index (e.g weight-for-age)

Anthropometric Indicators

The Building Blocks of Anthropometry: Indices

When two of these variables are used together they are called an index.

The Indices

I. Weight-for-age:

• identifies the condition of being underweight, for a specific age.

• reflects both past (chronic) and/or present (acute) undernutrition (although it is unable to distinguish between the two).

• Prevalence of underweight is a Millennium Development Goal Indicator.

II. Height-for-age:

• identifies past undernutrition or chronic malnutrition.

• For children below 2 years of age, the term is length-for-age; above 2 years of age, the index is referred to as height-for-age.

• Deficits in length-for-age or height-for-age is referred to as stunting.

III. Weight-for-height:

• identify children suffering from current or acute undernutrition or wasting

• useful when exact ages are difficult to determine.

• Appropriate for examining short-term effects such as seasonal changes in food supply or short-term nutritional stress brought about by illness.

The Equipments

• Scales

• Measuring boards

Length/Height Boards• Length/height boards should be designed to measure

children under 2 years of age lying down (recumbent), and older children standing up.

• The board should measure up to 120 cm (1.2 meters) for children and be readable to 0.1 of a centimeter.

• A measuring board should be lightweight, durable and have few moving parts.

How to compute Indices

Indices computation• Digital (using software like anthro, epinut,

nutrisurvey etc..)

• Manual (using formulas)

MUAC Tape

• This arm circumference insertion tape measures mid-upper arm circumference of children, up to 25 cm.

• Colour-coded in red/yellow/green, non-tear, stretch-resistant plasticized paper.

• Supplied in pack of tapes together with written and pictorial instructions for use

Assessing the Accuracy of Measurements

• Accuracy is achieved through good training and supervision

• When taking more than one height or weight measurement on the same person, the two measurements can be averaged.

• If they are vastly different from each other, the measurements should be disregarded and the measuring should start again (see table below)

Measurement Accuracy

Interpretation of the Indices• Taking age and sex into consideration,

• Measurements are expressed as follows::

– Z-score– Percent of the median– Percentiles

International Reference Standard Distribution

The Z-score or standard deviation unit (SD)

• is the difference between the value for an individual and the median value of the reference population for the same age or height, divided by the standard deviation of the reference population.

Percentage of the Median

• The median is the value at exactly the midpoint between the largest and smallest.

• If a child’s measurement is exactly the same as the median of the reference population we say that they are “100% of the median.”

Percentiles

• The percentile is the rank position of an individual on a given reference distribution, stated in terms of what percentage of the group the individual equals or exceeds.

• The distribution of Z-scores follows a normal (bell-shaped or Gaussian) distribution.

• The commonly used cut-offs of -3, -2, and -1 Zscores are, respectively, the 0.13th, 2.28th, and 15.8th percentiles.

• The percentiles can be thought of as the percentage of children in the reference population below the equivalent cutoff.

Percentiles

Stunted normal wasted

Z-scores Vs Percentiles

Percent of median VS Z-scores

• A comparison of cutoffs for percent of median and Z-scores illustrates the following:

90% = -1 Z-score80% = -2 Z-score

70% = -3 Z-score (approx.)

60% = -4 Z-score (approx.)

Uses of cut-offs

• The use of a cut-off enables the different individual measurements to be converted into prevalence statistics.

• Cut-offs are also used for identifying those children suffering from or at a higher risk of adverse outcomes.

• The most commonly-used cut-off with Z-scores is -2 standard deviations, irrespective of the indicator used.

• This means children with a Z-score for underweight, stunting or wasting, below -2 SD are considered moderately or severely malnourished. For example, a child with a Z-score for height-for-age of -2.56 is considered stunted, whereas a child with a Z-score of -1.78 is not classified as stunted.

Cut-offs…

• In the reference or healthy population, 15.8% would be below a cut-off of -1 SD; 2.28% of the children would be below -2 SD and 0.13% would be below -3 SD (a cut-off reflective of a severe condition)

• Cut-off points for MUAC for the 6 - 59 month age group– Below 12.5 cm with or without edema are classified as

moderate and severe– 11.0 cm can be used for screening severely malnourished

children

Cut-offs…

Malnutrition classification systems

The RTH (Road to Health) and Gomez classification systems typically useweight−for−age

Advantage: Differentiates between "wasting" and "stunting" Limitations: The need for height, weight and age and the relative complexity of the classification could be a disadvantage in some situations

The Welcome Classification

Indicator: Weight-for-age and edemaReference point: 50th centile of Harvard Standard

% expected Weight for Age

OEDEMA

Present Absent

80 - 60 Kwashiorkor Underweight

< 60 Marasmic-Kwashiorkor

Marasmus

Advantage: Useful for classifying more severe forms of malnutrition Limitations: Does not take account of height differences.

Age of the child must be known.

The Gomez Classification

% Expected Weight for Age

Category of Nutritional Status

>90% Normal

75 - <90% 1st degree malnutrition (mild)

60 - <75% 2nd degree malnutrition (moderate)

< 60% 3rd degree malnutrition (severe)

Indicator: Weight-for-age Reference point: 50th centile of Harvard Standard

Limitations: Does not take account of height differences. Age of the child must be known.

** Now used only in few countries

Common Terms for Acute Malnutritionfor Children 6-59 Months

GAM (Global Acute Malnutrition): • Is WFH < -2.0 Z-score or < 80.0% Median or MUAC

< 12.5 cm• With or with out edema• Refers to all moderate and severe malnutrition combined

SAM (Severe Acute Malnutrition): WFH < -3.0 Z-score or < 70.0% Median

• All with edema included.

Other Common Measures(BMI)

• BMI is defined as the individual's body weight divided by the square of their height.

• is a statistical measure of the weight of a person scaled according to height.

• As such, it is useful as a population measure only, and is not appropriate for diagnosing individuals.

• It was invented between 1830 and 1850 by the Belgian polymath Adolphe Quetelet during the course of developing "social physics"[1].

BMI cont…• is considered as a good index of body fat and

protein stores

• best used for individuals between the ages of 20 and 65 years-can be also used for children

• Can be determined using a BMI chart, which displays BMI as a function of weight (horizontal axis) and height (vertical axis) using contour lines for different values of BMI or colors for different BMI categories.

• The factors for US units are more precisely 703.0696 and 4.882428.

• The formulas universally used in medicine produce a unit of measure of kg/m2. Body mass index may be accurately calculated using either of the formulas below

• SI US

BMI InterpretationsCATEGORY

• STARVATION• UNDERWIEGHT• NORMAL• OVERWEIGHT• OBESE• MORIBDLY OBESE

RANGE (KG.M2)

• < 14.9• 15-18.4• 18.5-22.9• 23-27.5• 27.6-40• >40

LimitationsBecause BMI is dependent only upon weight and height,

it makes simplistic assumptions about distribution of muscle and bone mass, and thus

• May overestimate adiposity on those with more lean body mass (e.g. athletes) while

• underestimating adiposity on those with less lean body mass (e.g. the elderly). If taller people were simply scaled-up versions of shorter people,

• A further limitation relates to loss of height through aging-BMI will increase without any corresponding increase in weight.

• pregnancy and muscle builders

EDEMA (clinical)

Common Terms for Acute Malnutritionfor Children 6-59 Months

GAM (Global Acute Malnutrition): • WFH < -2.0 Z-score or • < 80.0 percent Median or • MUAC < 12.5 cm

• With or with out edema• Refers to all moderate and severe malnutrition combined

SAM (Severe Acute Malnutrition):

WFH < -3.0 Z-score or

< 70.0 percent Median

MUAC < 11.0 cm• All with edema included.

Figure 1:Generalized scheme of the development of deficiency

Source: UNU, 1972

Design of NA Systems

The assessment system and the type and number of measurements selected will depend on a variety of factors:• Objectives • Methodological issues• Cost etc...

As a general rule. Specific data are often better collected in a separate survey unless it is important to examine interactions with anthropometry or mortality

Examples Objectives Scopes

• To estimate prevalence of malnutrition

Surveys

• To evaluate impact of intervention

Surveillance

• To identify malnourished individuals

Screening

• Methodological issues validity, precision, etc..

• Other actors Logistics