Biochemistry

Hypoalbuminemia is often erroneously used as an index of undernutrition. However, the diagnostic specificity of this index is poor. Serum albumin levels are determined by a complex interplay between nutritional intake, total body albumin distribution, and several pathological changes that alter the biosynthetic and catabolic rates of albumin. In the acutely ill or stressed older person, cytokine release suppresses albumin and prealbumin synthesis. Additionally, the release of catabolic counter-regulatory hormones in stressful situations reduces albumin synthesis even further. Direct downregulation of albumin gene expression also occurs in situations of acute stress. Paradoxically, undernutrition itself may result in a compensatory reduction in albumin catabolism, yielding inappropriately high albumin levels. Although serum albumin is a poor index of undernutrition, hypo-albuminemia is linked with frailty, excess comorbidity and increased mortality in older adults. Thus, the clinical relevance of hypoalbuminemia lies in the identification of a high-risk subset of older persons in whom early and aggressive nutritional intervention is crucial.

Several other biochemical indices are used as nutritional markers. However, like albumin, they lack diagnostic specificity and have relatively long half-lives, which limit their value in the serial evaluation of undernutrition. Insulin-like growth factor 1 is considered to have the greatest positive predictive value as it has been shown to correlate well with nutritional status even during periods of acute stress. Added advantages of this index are a relatively short half-life of 2-6 h and a rapid response to fasting and refeeding. Nonetheless, routine use of this assay in the evaluation of under-nutrition is precluded by cost. Overall, for practical clinical purposes, the use of biochemical markers in routine nutritional geriatric management is cost-ineffective and unreliable.

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