LABORATORY DATA
There are numerous biochemical parameters that can be measured to assess the nutritional status of the individual. These parameters are used to complement the medical history and the physical exploration. Besides, the general laboratory tests to establish the nutritional status of the patient, especially relevant are protein analysis, immunological function and other hormone parameters.
Proteins
Approximately 15% of our body weight corresponds to proteins. The largest amount of proteins is found in skeletal muscle known as somatic proteins; the rest of proteins constitute cells and the blood and are known as visceral proteins.
a) Evaluation of visceral proteins
Albumin: eThis is one of the most widely used parameters in nutritional assessment. Its normal value is above 3.5 mg/dl; between 3.5 and 3 mg7dl it is considered mild malnutrition, between 2.1 and 3 mg/dl it is considered moderate malnutrition and below 2.1 mg7dl it is defined as severe malnutrition. It is useful if this parameter is considered at long term, as albumin has a mid life of 14 to o18 days, not being assessable for short-term nutritional assessment.
Transferin: It is generally accepted that levels between 150-200 mg/dl indicate a mild deficit, between 100 and 150 mg/dl a moderate deficit, and less than 100 mg/dl is considered as a severe depletion. Its main advantage over albumin is that it has a mid-life of 8 to 10 days , and is useful in short and midterm nutritional assessment.
Prealbumin: It is synthesised in the liver. It is very useful in short-term nutritional assessment and to assess the response to nutritional treatment as it has a 2 day mid-life.
Retinol binding protein: It has a shorter mid life, of about 12 hours, and is thus very useful to detect sharp changes in the nutritional status of the patient.
b) Evaluation of somatic proteins
Urinary excretion of creatinine: Creatinine is a muscle product, as thus its evaluation is a direct indicator of muscle mass (1 gram of creatinine equates approximately 18 g of muscle mass). An index correlating elimination of creatinine in the urine with the height of the patient has been elaborated; it is considered normal when the index is above 80%, between 60-80% it indicates a moderate deficit of muscle mass and below 60% a severe deficit.
c) Other tests
Other tests that evaluate protein metabolism are the evaluation of nitrogen balance and the profile of serum amino acids.
Immunological Function Tests
All immune responses are affected by a situation of nutritional deficit. Nonetheless, these tests are not very specific as they can be altered by several situations.
The most popular ones are lymphocyte count (lymphocyte count below 1200-1500/mm3 indicates mild malnutrition, when values are below 800 lymphocytes/mm3 there is severe deficiency severe) and delayed sensitivity tests (subcutaneous injection of certain antigens, to observe the immune response of the body), T lymphocyte count, immunoglobulin determination, presence of mitogens, and C3 fraction determination of the complement.
Other Parameters
Hormone parameters such as the assessment of thyroid function or growth hormone have also been used in the assessment of the nutritional status.
Assessment of muscle and respiratory function is also performed in patients using dynamometry and expiratory flow measurements. These measurements are very useful in malnourished patients, as these are the first parameters to undergo changes once adequate nutritional support has been restored.