Laboratory criteria for malnutrition

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

Indicator	Degree of malnutrition
	Lightweight	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, ME / l	3000-2600	2500-2200	Below 2200
Lymphocytes × 10 9 / l	1.8-1.5	1.5-0.9	Less than 0.9

Using cholesterol as a marker of nutritional status is now more useful than previously thought. A decrease in serum cholesterol concentration below 3.36 mmol / L (130 mg / dL) is very significant from a clinical point of view, and a concentration below 2.33 mmol / L (90 mg / dL) can be an indicator of severe malnutrition and a prognostic factor. Adverse outcome.

Nitrogen balance

The balance of nitrogen in the body (the difference between the amount of consumed and excreted nitrogen) is one of the widely used indicators of protein metabolism. In a healthy person, the rates of anabolism and catabolism are in balance, therefore 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. When recovering, the nitrogenous balance should become positive due to protein intake from food. The study of nitrogen balance provides more complete information about the condition of the patient with metabolic requirements for nitrogen. Evaluation of nitrogen excretion in critical patients allows to judge the amount of nitrogen lost as a result of proteolysis.

To assess the nitrogen balance, two methods of measuring nitrogen losses in the urine are used:

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

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

This indicator (AB) is one of the most reliable criteria for assessing the protein metabolism of the body. It allows timely identification of the catabolic stage of the pathological process, assessment of the effectiveness of nutrition correction and the dynamics of anabolic processes. It was found that in cases of correction of the pronounced catabolic process, it is necessary to bring the nitrogenous balance using artificial nutrition to + 4-6 g / day. It is important to monitor the excretion of nitrogen every day.

Direct determination of total nitrogen in the urine is preferable to urea nitrogen testing, especially in critical patients. Normal allocation of total nitrogen in the urine is 10-15 g / day, its percentage is distributed as follows: 85% - urea nitrogen, 3% - ammonium, 5% - creatinine, 1% - uric acid. AB calculation for total nitrogen is carried out according to the following formula: AB = [incoming protein (g) / 6.25] - [daily loss of total nitrogen (g) + 4].

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

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

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

Urinary excretion of urea is widely used to assess the effectiveness of parenteral nutrition using sources of amino nitrogen. Reduction of urea excretion with urine should be considered an indicator of the stabilization of trophic status.

The results of laboratory tests allow to determine the risk groups for the development of complications caused by malnutrition and inflammatory reactions in critically ill patients, in particular, by calculating the prognostic inflammatory and nutritional index (PINI) using the following formula: PINI = [Acid a1-glycoprotein (mg / l) × CRP (mg / l)] [[albumin (g / l) × prealbumin (mg / l)]. In accordance with the PINI index, risk groups are distributed as follows:

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

[1], [2], [3]

Antioxidant status

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

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

[4], [5], [6], [7], [8], [9], [10]