Impact of disease on markers of macronutrient status

It is apparent that illness, particularly acute illness, affects most tests which are used to assess macronutrient status. In acutely-ill patients, the best tests in terms of specificity for nutritional status are in vivo neutron-activation analysis for body composition and N balance as an assessment of recent intake. Changes in plasma protein concentration must be interpreted with great care, and this is best done in conjunction with changes in the acute-phase-protein response. Measurement of plasma IGF-1 may be helpful in the presence of an acute-phase response, but this requires further validation. In many such patients, the most important part of the assessment continues to be the clinical and dietary history, together with a careful physical examination. However, the need for accurate measurement remains, so that nutritional status and its progress can be accurately quantified. This was best expressed many years ago by William Thompson, Lord Kelvin, when he stated '... when you can measure what you are speaking about and express it in numbers you know something about it... when you cannot express it in numbers your knowledge is of a meagre and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced to the stage of science...'.