Growth trends and nutritional status of a child/community can be evaluated by means of field surveys, with the help of clinical examination, anthropometric measurements, biochemical tests and dietary intake along with information on socio-economic, demographic and ecological variables. Nutritional anthropometry is concerned with the measurement of the physical dimensions and the gross composition of human body at different age levels. However, it does not give specific information about the nutrients. For that information a variety of biochemical tests are useful. Although biochemical estimations of nutritional significance can be carried out on a variety of body tissues including liver, muscle and bone. In practice in field surveys, tests are confined to two fairly easily obtainable body fluids, blood and urine. Laboratory tests can be altered by medications, hydration status, disease status or other metabolic process such as stress. Biochemical tests can be employed to test the relative adequacy of dietary intake, metabolic changes due to tissue malnutrition and depletion of body stores of proteins. Alterations in amino acid metabolism have been demonstrated in Kwashiorkor caused by enzyme defects and inadequacy of plasma proteins especially albumin.
Plasma from blood sample is required for examinations for albumin, vitamin A, carotene, ascorbic acid and alkaline phosphatase. Fresh whole blood is used for the determination of haemoglobin. Anaemia can occur from iron deficiency of various nutrients. The principal ones are iron, folic acid and vitamin B12. Iron deficiency may exist in the body as a result of inadequate dietary intake, poor absorption or a combination of both. This is especially likely to happen in early childhood when the iron needs are high and the food eaten tends to be poor source of iron. We can detect anaemia by testing haemoglobin levels of children/ population and can compare these with standards of haemoglobin suitable for the particular age groups. Haemoglobin levels are independent of climate, but attention may be paid to the effects of high altitude as well as other causes of anaemia, such as malaria, sickle cell diseases and folic acid deficiency. Urine samples are used for detection of urea, thiamine, urinary iodine, and riboflavin etc. However, when used as a measure of body muscle mass for creatinine estimation, urine has to be collected over a time period- minimally three hours and preferably twenty four hours. Creatinine, a product of muscle metabolism is excreted into the urine and can provide accurate estimate of muscle mass utilisation. This measurement can be affected greatly by renal function.
Biochemical investigation may give information on the nutrient supply to the body as reflected by levels in a particular tissue, most often the serum, e.g., ascorbic acid. However, the concentration of an essential nutrient in a body fluid may be reduced as a result of dietary deficiency, poor absorption, impaired transport (as can result from plasma protein in protein calorie malnutrition), abnormal utilisation or a combination of these. While the measurement of nutrient concentration is helpful in suggesting the possibility of malnutrition, it does not indicate the presence or define the degree of nutritional disease.
Some biochemical test can be undertaken that reveal metabolic changes resulting from tissue malnutrition due to inadequate levels of essential nutrients, often of long duration. The detection of such metabolic changes aids in the assessment of nutritional status and in many instances indicates a state of deficiency with greater certainty than does a mere lowering of tissue concentration of essential nutrients. These changes sometimes precede the appearance of clinical manifestation of malnutrition. A decreased availability of iodine to the thyroid may be the result of its inadequate intake and can be detected as thyroid enlargement especially in school children. The nutritional significance of the results of biochemical tests in a community has to be correlated with all the other findings i.e. clinical, anthropometric, dietary and ecological.