Biological markers of protein-energy malnutrition

The biological markers of undernutrition fall into three categories: (a) those that measure structure; (b) those that measure function; and (c) indices of the above two. Ideally a marker of nutritional status should have the following characteristics: specific to nutritional status; sensitive to changes in nutritional status; reproducible; simple to measure; inexpensive and widely available. Unfortunately there are no such markers, and therefore individuals involved in the assessment of nutritional status should be aware of the advantages and disadvantages of the markers they use. For example, body composition can be assessed using sophisticated techniques that make fewer assumptions than simple bedside techniques (1). However, these sophisticated techniques (eg neutron activation, and combinations of techniques such as hydrodensitometry, water dilution techniques and dual-energy X-ray absorptiometry) are not widely available and some of them are labour intensive. On the other hand simple bedside techniques, such as those based on skinfold thicknesses can be applied widely because they are easy and quick to perform, but they are probably not as accurate as the classic body composition techniques (hydrodensitometry or water dilution techniques) or other sophisticated methods based on the assessment of multiple body compartments (1). Therefore the choice of method depends not only on the availability of investigative tools, but also on the practicalities of using them in individuals, a small group of individuals, or large groups of individuals, (eg national surveys during famine and non-famine conditions). In this brief review only some aspects concerned with simple bedside or laboratory methods will be discussed.