INVESTIGATING NUTRITIONAL DISORDERS
The main objectives in investigating nutritional disorders are to detect malnutrition, determine the most appropriate treatment and to monitor the progress of the patient during treatment. A number of fairly general investigations are available for patients suspected of suffering from malnourishment, for example taking a medical history, physical examination and laboratory investigations. A patient’s medical history may help to reveal the underlying basis of the complaint. A significant part is determining the dietary history, which usually involves dietary recall of the last one to seven days, or food frequency questionnaires where patients estimate how often a particular food on a list has been eaten. A medical history also includes specific questions concerning recent weight changes, dietary habits, for example alcohol consumption, appetite, GIT function, use of vitamin and mineral supplements and drug intake. A physical examination can include anthropometric measurements, such as weight, height, body mass index , arm circumference and skinfold thickness. Arm circumference is an indicator of muscle mass. The arm circumference is measured at the midarm point in millimeters (Figure 10.35) and values are typically 293 mm in males and 285 mm in females. Skinfold thickness indicates the extent of subcutaneous fat stores. It is commonly measured at the biceps, triceps, subscapular and suprailiac sites in both males and females. In, for example, the triceps measurement the arm is allowed to hang freely and a fold of skin above the midpoint of the arm is pulled from the underlying muscle and measured to the nearest millimeter using calipers (Figure 10.36). Values are typically 12.5 and 16.5 mm for males and females respectively. Measurements at the four sites should be made in duplicate and should not vary by more than 1 mm. If consecutive measurements become increasingly smaller the fat is being compressed and other sites should be assessed while the tissue recovers. However, the accuracy of the test depends upon selecting the sites correctly, an appropriate technique in taking the measurements and the experience of the tester; hence the trend is more important than the values at any one time. Values for arm circumference and skinfold thickness are compared with standard values for the same sex. Undernutrition is indicated if they are less than 90% of these values.
The appearance of the skin, hair, nails, eyes, bones, teeth and mucous membranes may reveal signs of malnutrition. A number of general laboratory-based investigations on blood and urine samples can aid in diagnosing malnutrition and are listed in Table 10.8. These tests are not reliable when used in isolation, as their findings are also altered in some disease states. Hair and nail samples are of questionable clinical value and are not routinely taken.