How protein status is measured?

Measurement of protein status:

Protein is macronutrient and polymer of amino acids linked through a peptide bond. Proteins are structural component of cells, tissues, muscles, skin and bones and play an important role in body functioning.

Proteins are an integral part of enzymes, hormones, and antibodies. Moreover, proteins serve as a carrier, hemoglobin carries oxygen and transport it to every cell of the body.

Protein is an essential energy - yielding nutrient and its deficiency result into one of the most prevalent nutritional disorder commonly known as protein- energy Malnutrition (PEM). PEM is broadly classified as marasmus(deficiency in caloric intake ),

kwashiorkor(marked caloric and protein deficiency signs present , sometimes termed as the most severe from of malnutrition). PEM is associated with chronic diseases, clearly gaining higher concern in developing countries due to high infant mortality. Apart, it is a common concern of individuals having AIDS, cancer etc.

Assessment of protein deficiency is to explicate, prevent and treat PEM. Biochemical assessment provides accurate data or more complete picture of protein status.

Somatic and visceral proteins can be assessed through biochemical analysis Somatic protein is present in the skeletal muscle where as visceral protein is present in visceral parts of the body (liver, heart, pancreas etc), red blood cells, white blood cells and serum.

Somatic and visceral proteins constitute approximately 30-50%of the total body proteins. Remaining protein is present in skin and connective tissue(bones, cartilage, matrix, and ligaments).

Somatic compartment remains homogenous, hundred of different protein pools exist in the visceral part performing specific function with in the body.

Creatinine analysis;

The test is used to estimate the 24 hours urinary creatinine execration creatinine (a product of skeletal muscle) is execrated constant proportion to muscle of body.

Lean mass could either be assessed by comparison of 24 hours urinary creatinine execration with standard value based on stature or form reference value of male (23mg/kg) and female (18mg/kg) based on their recommended ideal body weight, respectively.

Another method to calculate creatinine height index (CHI)''It is a ratio of a patient' s measured 24 hours urinary creatinine execration and the expected execration of a reference adult of the same sex and stature''.

The CHI value are expressed in percent terms. The CHI range of 60 -80% indicate mild depletion 40-60% shows moderate depletion, while the vaue lower than 40% are indicative of sever depletion. The primary caution in this analysis is to collect urine for exactly 24-hour.

Factors such as diet, inappropriate use of height and weight table based on sex and stature and usage of urine sample collected over less than 24 - hours could affect the creatinine value.

Adult male

Height(cm)

157.5 160.0 162.6 165.1 167.6 170.2 172.7 175.3 177.8 180.3 182.9 185.4 188.0 190.5 193.0

Creatinine(mg)

1288 1325 1359 1386 1426 1467 1513 1555

1596 1642 1691 1739 1785 1831 1891

Adult female

height(cm)

147,3 149.9 152.4 154.9 157.5 160.0 162.6 165.1 167.6 170.2 172.7 175.3 177.8 180.3

182.9

Creatinine(mg)

830 851 875 900 925 949 977 1006 1044

1076 1109 1141 1174 1206 1240

Serum protein;

Serum protein analysis is simple and accurate method to screen the patient at risk of medical complications and determine the response of nutritional support. Serum protein levels decrease either due to decrease production of protein from liver or due to poor nutritional status. The following serum protein are measured to determine the protein status.

A) Albumin;

Albumin is globular protein synthesized by the liver. Serum albumin levels indicate both dietary inadequacy and depleted protein reserve due to pathological conditions. Low serum albumin is a risk factor for higher morbidity in patients.

Because of large pool( 4-5kg body weight ) and long half- life, serum albumin level responds slowly to any nutritional change. Once serum albumin level begin to fall, extravascular albumin moves inward to maintain the normal values. Thus it is not a sensitive indicator of PEM .

B) Transferrin;

It is beta globulin protein synthesized by the liver, subsequently transferred to the blood and binds with iron and plasma . Its smaller pool and shorter life make it a better index for any changes in protein status when compared to albumin .

Depending upon the nature of biochemical analysis, serum transferrin could either be determined directly through radial immunodiffusion and nephelometry or indirectly (most common) by total iron binding capacity(TIBC).

Low level of serum transferrin may indicate chronic infections(enteropathy, nephropathy, liver diseases hemolytic anemia) while higher level reveal the presence of iron - deficiency anemia.

C) Pre albumin;

Pre albumin also called transthyretin and thyroxine- binding pre albumin is synthesized with in the liver . It serves as a transport protein for thyroxine ( T4) and a carrier for retinol- binding protein . short pool(0.01g/kg) and short half- life (2-3 days ) of pre albumin , make it pronounced biomarker when compared to albumin and transferrin.

It is a sensitive indicator of initial stages of malnutrition normality as its level rapidly falls in PEM. However, its level return to normality as soon as protein status is improved therefore, is not support recommended as a clinical endpoint for termination of nutritional support.

Pre albumin level varies in liver disease, sepsis, chronic renal failure , dialysis and acute catabolic state (surgery and trauma).

D) Retinol- binding protein;

Retinol binding protein is is liver synthesized protein, act as a carrier for retinol by forming a complex with pre albumin . It circulates in blood with retinol and pre albumin as a trimolecular complex, in a ratio 1:1:1.

Its smaller pool90.002g/kg) and half -life (about 12 hours) made it favorable for for precise measurement of protein energy deficiency . Different condition/ disease like acute catabolic state and vitamin A deficiency lowered the serum retinol -binding protein.