Serum markers

Biochemical evaluation of the protein component of trophic nutrition status involves the determination of the concentration of various proteins in the patient's blood serum. The main organ of synthesis of whey protein markers is the liver, it is also the first of the organs that are affected in the syndrome of malnutrition. In Table.the spectrum of serum proteins used as indicators in assessing the nutritional status is presented. All these proteins perform transport functions.

An ideal marker for assessing short-term changes in protein status should have a small pool in serum, a high synthesis rate, a short half-life, a specific

response to protein deficiency and a lack of response to factors not related to nutrition.

Table Serum proteins used for nutritional assessment

Table Serum proteins used for food evaluation

Albumin is the first biochemical marker of eating disorders, the definition of which has been used for a long time in clinical practice. In the human body there is a relatively large pool of albumin, more than half of which is outside the vascular bed. The concentration of albumin in the blood serum reflects changes occurring within the vascular bed. Because of the rather long half-life( 21 days), albumin does not belong to the sensitive indicators of short-term protein deficiency in the body or markers of the efficiency of nutrition correction. Redistribution of albumin from extravascular space to intravascular space also reduces its indicator capabilities. Albumin well helps to identify patients with chronic protein deficiency leading to hypoalbuminemia, provided adequate intake of non-protein calories.

The concentration of albumin in the serum depends on liver and kidney disease, as well as on the hydration of the patient. Age also affects the concentration of albumin, which decreases with its increase, probably due to a decrease in the rate of synthesis.

Transferrin - r-globulin, which, in contrast to albumin, is almost entirely in the intravascular canal, where it functions as an iron transport. Transferrin has a short half-life( 8 days) and a significantly smaller pool compared to albumin, which improves its ability as an indicator of the status of protein status. Nevertheless, the concentration of transferrin in the serum is affected by iron deficiency in the body, pregnancy, gastrointestinal diseases, liver, kidney, oral contraceptives, antibiotics in high doses, and neoplastic processes.

Vitamin A-binding protein has a very short half-life( 12 hours) and a low pool, so its concentration quickly decreases with protein and calorie deficit and reacts quickly to nutritional correction. Nevertheless, the concentration of vitamin A-binding protein in the

blood is altered by liver disease, vitamin A deficiency, acute catabolic conditions, after surgery and hyperthyroidism.

Prealbumin, or transthyretin, has a half-life of 2 days and a slightly higher pool in serum than vitamin A-binding protein;but is characterized by the same sensitivity to protein deficiency and nutrition correction. In patients with ARI, an increase in the concentration of prealbumin in the blood serum is possible because of the role of the kidney in its catabolism. Prealbumin is a negative protein of the acute phase of inflammatory processes( its concentration in the blood serum decreases with inflammation).Therefore, in order to differentiate the inflammatory decrease in prealbumin concentration from disturbances in the nutritional status, it is necessary to simultaneously determine another acute phase protein( eg, CRP or orosomucoid).If the concentration of CRP is normal, then the low concentration of prealbumin is most likely due to protein deficiency. Conversely, with a high content of CRP, a low concentration of prealbumin can not be regarded as a sign of a malnutrition. During the monitoring of the nutrition correction of patients with a decreasing concentration of CRP and an increasing content of prealbumin, it can be regarded as probably having a tendency to improve the protein-energy status. Once the concentration of cPb returns to normal, prealbumin becomes an objective indicator of the nutritional status of the patient. The determination of prealbumin concentration is especially useful in intensive care patients in the severe state at the onset of parenteral artificial feeding and in monitoring the response to such therapy. The concentration of serum prealbumin above 110 mg / l is regarded as an indicator indicating the possibility of transferring the patient from parenteral nutrition to enteral. If the concentration of prealbumin does not increase with parenteral nutrition or remains below 110 mg / l, it is necessary to review the diet, the amount of nutrients, or look for complications of the underlying disease [Davies B. G. et al., 1999].

Fibronectin is a glycoprotein found in lymph, blood, basal membranes and on the surface of many cells performing structural and protective functions. Determining the concentration of fibronectin in the blood plasma in combination with other nutritional indices is important, as it is one of the few markers synthesized not only in the liver. With adequate enteral / parenteral nutrition, the concentration of fibronectin in the blood plasma increases 1-4 days after the start of therapy.

Somatomedin C, or insulin-like growth factor( IGFR) I, has a structure similar to insulin, and has a pronounced anabolic effect. In the blood, somatomedin C circulates being bound to carrier proteins;his half-life is several hours. Because of this low half-life and sensitivity to nutritional status, somatomedin C is considered the most sensitive and specific marker of nutritional status. Reduction of its concentration is possible in patients with insufficient thyroid function( hypothyroidism) and with the administration of estrogens.

Although the determination of the concentrations of fibronectin and soma-tomedidine C has advantages in assessing nutritional status compared to other markers, their use in clinical practice is currently limited due to the high cost of these assays.

To assess the subclinical forms of protein deficiency and to quickly monitor the effectiveness of therapy, one can also use methods to determine the ratio of some amino acids in plasma, as well as the activity of serum cholinesterase.

Along with the listed indicators that allow us to assess the severity of protein deficiency, the definition of the absolute number of lymphocytes in the blood is simple and informative. By their content, it is possible in general terms to characterize the state of the immune system, the severity of which is correlated with the degree of protein deficiency. If the protein-caloric nutrition is insufficient, the amount of lymphocytes in the blood often decreases less than 2.5x109 / l. The lymphocyte content of 0.8-1.2x109 / l indicates a moderate nutritional deficiency, and less than 0.8x109 / l indicates a pronounced deficit. Obvious absolute lymphopenia in the absence of other causes of immunodeficiency allows the clinician to assume insufficient nutrition.

Changes in laboratory indicators for different degrees of malnutrition are presented in the table.

Table Laboratory criteria for malnutrition

Table Laboratory criteria for nutritional deficiency

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

The use of cholesterol as a nutritional status marker is now more useful than previously thought. Reducing serum cholesterol concentrations 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 prognostic factoran unfavorable outcome.