Laboratory criteria for malnutrition

In addition to protein status markers, other laboratory indicators are also used in clinical practice to assess the state of carbohydrate, lipid, mineral and other types of metabolism.

Indicator	Degree of malnutrition
	Light	Average	Heavy
Total protein, g/l	61-58	57-51	Less than 51
Albumin, g/l	35-30	30-25	Less than 25
Prealbumin, mg/l	-	150-100	Less than 100
Transferrin, g/l	2.0-1.8	1.8-1.6	Less than 1.6
Cholinesterase, IU/l	3000-2600	2500-2200	Below 2200
Lymphocytes, ×10 9 /l	1.8-1.5	1.5-0.9	Less than 0.9

The use of cholesterol as a marker of nutritional status now appears to be more useful than previously thought. A decrease in serum cholesterol concentration below 3.36 mmol/L (130 mg/dL) is clinically significant, and a concentration below 2.33 mmol/L (90 mg/dL) may be an indicator of severe malnutrition and a predictor of poor outcome.

Nitrogen balance

The nitrogen balance in the body (the difference between the amount of nitrogen consumed and excreted) is one of the widely used indicators of protein metabolism. In a healthy person, the rates of anabolism and catabolism are in equilibrium, so the nitrogen balance is zero. In case of injury or stress, such as burns, nitrogen consumption decreases and nitrogen losses increase, as a result of which the patient's nitrogen balance becomes negative. During recovery, the nitrogen balance should become positive due to protein intake with food. A study of the nitrogen balance provides more complete information about the condition of a patient with metabolic needs for nitrogen. Evaluation of nitrogen excretion in critically ill patients allows us to judge the amount of nitrogen lost as a result of proteolysis.

To assess nitrogen balance, two methods are used to measure nitrogen loss in urine:

• measurement of urea nitrogen in daily urine and a calculation method for determining total nitrogen loss;
• direct measurement of total nitrogen in daily urine.

Total nitrogen includes all protein metabolism products excreted in the urine. The amount of total nitrogen is comparable to the nitrogen of digested protein and is approximately 85% of the nitrogen received with food proteins. Proteins contain an average of 16% nitrogen, therefore, 1 g of excreted nitrogen corresponds to 6.25 g of protein. Determining the daily excretion of urea nitrogen in the urine allows for a satisfactory assessment of the nitrogen balance (NB) with the maximum possible accounting of protein intake: NB = [protein received (g)/6.25] - [daily urea nitrogen losses (g) + 3], where the number 3 reflects the approximate nitrogen losses with feces, etc.

This indicator (AB) is one of the most reliable criteria for assessing protein metabolism in the body. It allows timely detection of the catabolic stage of the pathological process, assessment of the effectiveness of nutritional correction and the dynamics of anabolic processes. It has been established that in cases of correction of a pronounced catabolic process, it is necessary to bring the nitrogen balance with the help of artificial nutrition to +4-6 g / day. It is important to monitor nitrogen excretion from day to day

Direct determination of total nitrogen in urine is preferable to the study of urea nitrogen, especially in critically ill patients. The excretion of total nitrogen in urine is normally 10-15 g/day, its percentage content is distributed as follows: 85% - urea nitrogen, 3% - ammonium, 5% - creatinine, 1% - uric acid. Calculation of AB for total nitrogen is carried out according to the following formula: AB = [received protein (g)/6.25] - [daily loss of total nitrogen (g) + 4].

Determination of total nitrogen in urine during the initial catabolic stage should be carried out every other day, and then once a week.

An important criterion, complementing all of the above, is the determination of the excretion of creatinine and urea in the urine.

Creatinine excretion reflects muscle protein metabolism. Normal daily urinary creatinine excretion is 23 mg/kg for men and 18 mg/kg for women. With muscle wasting, urinary creatinine excretion and the creatinine-growth index decrease. The hypermetabolic response that occurs in most patients with emergency conditions is characterized by an increase in total metabolic costs, which accelerates muscle loss. In such patients in a state of catabolism, the main goal of maintenance nutrition is to minimize muscle loss.

Urea excretion in urine is widely used to assess the effectiveness of parenteral nutrition using amino nitrogen sources. A decrease in urea excretion in urine should be considered an indicator of stabilization of the trophic status.

Laboratory test results help to identify risk groups for the development of complications caused by malnutrition and inflammatory reactions in critically ill patients, in particular by calculating the Prognostic Inflamatory and Nutritional Index (PINI) using the following formula: PINI = [Acid a1-glycoprotein (mg/L)×CRP (mg/L)]/[albumin (g/L)×prealbumin (mg/L)]. According to the PINI index, risk groups are distributed as follows:

• below 1 - healthy condition;
• 1-10 - low risk group;
• 11-20 - high risk group;
• more than 30 - critical condition.

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Antioxidant status

The formation of free radicals is a constant process in the body, physiologically balanced by the activity of endogenous antioxidant systems. With an excessive increase in the production of free radicals due to prooxidant effects and / or failure of antioxidant protection, oxidative stress develops, accompanied by damage to proteins, lipids and DNA. These processes are significantly enhanced against the background of a decrease in the activity of antioxidant systems of the body (superoxide dismutase, glutathione peroxidase (GP), vitamin E, vitamin A, selenium), protecting cells and tissues from the destructive effects of free radicals. In the future, this leads to the development of the main diseases of mankind: atherosclerosis, coronary heart disease, diabetes mellitus, arterial hypertension, immunodeficiency states, malignant neoplasms and premature aging.

Modern laboratory tests allow us to assess both the activity of free radical processes and the state of antioxidant defense systems.

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