Screening biochemical measurements

Function of mitochondria is also commonly monitored as an indicator of cellular toxicity. Mitochondrial uptake and retention of the fluorescent dye, rhodamine 123, can be visualized microscopically. Biochemical measurements of mitochondrial function include the ATP-ADP ratio and dehydrogenase activity with MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide), which yields a colored formazan product upon reduction. The dye, neutral red (3-amino-7-dimethyl-amino-2-methylphenazine hydrochloride), targets lysosomes, and its retention is inversely related to cytotoxicity. Commercially available versions of the MTT and neutral red assays have been adapted to microtiter plate formats to provide highly efficient screening assays. Examples of how cell-type-specific functions can be followed as indicators of cell toxicity are included in Table 8.1. 

The tools for nutritional assessment include medical history and screening aides, physical examination and anthropometric measurements, biochemical assessment, and tests of immune function. A general health assessment and medical history are required to rule out causes of secondary malnutrition such as poor oral health, chronic illness, disease, and medication. Malnutrition is influenced by lifestyle, which includes alcohol usage in adults, food preference, eating habits, social interactions, and economic status. Various screening tools, such as the DETERMINE checklist (White et al., 1991), are available to assess the risk of malnutrition. 

While low serum cholesterol levels have been observed in malnourished patients, largely as a result of decreased synthesis of lipoproteins in the liver, hypocholesterolemia occurs later in the course of malnutrition and is therefore not useful as a screening test. PEM usually results in low serum urea nitrogen (BUN), urinary urea, and total nitrogen. Estimation of 24-h urine creatinine excretion is also a valuable biochemical index of muscle mass (when there is no impairment in renal function). The urinary CHI is correlated to lean body mass and anthropometric measurements. In edematous patients, for whom the extracellular fluids contribute to body weight and spuriously high body mass index values, the decreased CHI values are especially useful in diagnosing malnutrition. 

The diagnosis of HH is established based on serum transferrin saturation (TS), defined as serum iron divided by total iron binding capacity (TIBC). Since serum iron and ferritin levels lack specificity for diagnosis when used alone, measurement of fasting TS is currendy recommended as a first screen to detect iron overload. TS is the best indirect biochemical marker of iron stores. A fasting TS of greater than 45% will detect over 98% of all cases of phenotypic hemochromatosis (Tavill, 2001). 

A fast biological screen will necessarily be only a crude approximation of the clinical situation. To get useful biological data it is still necessary to focus on the (often hypothetical) biochemical mechanism explaining the reasons for a disease. The mechanism has to be expressed in biological activities, which can be measured in HTS, e.g. receptor affinities and enzyme inhibition. 

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