SERUM OR PLASMA TOTAL PROTEIN Human plasma is 97% V/V water. Of the remaining 3% occupied by solids, over 95% is occupied by proteins. There are more than 50 groups of protein known to exist in plasma of which over 95% can be accounted for by 13 proteins. These proteins includes: (albumin, a1-antitrypsin, a1-acid glycoprotein, a – lipoprotein, transferrin, complements, fibrinogen, IgA, IgG and IgM).

Function of plasma or serum proteins Individual proteins have specific functions which include:- 1- Transport, e.g.: bilirubin, metals, hormones. 2- Colloid osmotic pressure, mainly albumin. 3- Active enzymes, e.g.: complements, clotting factor. 4- Enzyme inhibitors, e.g.: antiproteases. 5- Humoral immunity, e.g.: immunoglobulins, complements. 6- Endogenous source of aminoacids.

Synthesis and degradation About (85) % of all plasma proteins are synthesized in the liver. The bulk of the remainder (particularly immunoglobulins) are synthesized by plasma cells and cells of reticuloendothelial system while the site of synthesis of most plasma proteins is known with some certainty; the site of degradation is far from clear. Most proteins are degraded by most tissues. Important sites of degradation include the: liver, gut, muscle and kidney. The control of protein synthesis and degradation is complex and often include factors such as dietary status, circulating plasma level (feed back), hormonal and neural.

Clinical significance Normal range of serum total protein is 64-83 g/L (6.4-8.3 g/dl). There are two general causes for alteration of serum total protein: 1. Change in the volume of plasma water. 2. Change in the concentration of one or more of the specific proteins. Decrease in the volume of plasma water (haemoconcentration) as occurs in dehydration due to inadequate water intake or to excessive water loss due to vomiting, diarrhea or burn is reflected as hyperproteinemia (with the concentration of all individual proteins are increased). Haemodilution (increase in plasma water volume) is reflected as hypoproteinemia. This occurs with water intoxication and massive intravenous infusions.

Of the individual serum proteins, albumin is present in such high concentration that low level of this protein alone causes hypoproteinemia A mild hyperproteinemia may be caused by an increase in the concentration of specific proteins as increase in acute phase proteins and polyclonal immunoglobulins as a result of infection, chronic inflammation, chronic hepatitis and liver cirrhosis. Marked hyperproteinemia may be caused by high levels of the monoclonal immunoglobulin, produced in multiple myeloma.

Investigations of protein disorders In general, the following tests are usually requested to characterise the pattern of abnormality. These include:- 1- Serum total protein. 2- Serum albumin. 3- Serum albumin: globulin ratio, where globulin = total protein – albumin and normal range for A:G ratio is 1.3-1.8 4- Serum protein electrophoresis where different fractions of protein are separated. 5- Measurement of specific protein concentrations.

Biuret method for measuring total protein . Biuret method for measuring total protein Principle Peptide bonds (– C – N – ) of proteins react with cupir ions in alkaline solution to form a violet colour product whose absorbance at 540 nm is proportional to the concentration of protein.

Procedure 1- Set up a set of the following tubes Test: 0.02 ml serum + 1.0 ml of Biuret reagent. Standard: 0.02 ml of standard solution+1.0 ml of Biuret reagent. Blank: 0.02 ml distilled water + 1.0 ml of Biuret reagent. 2- Mix, incubate for 30 min. at 20 to 25 c before reading. 3- Read absorbances of solutions at 540 nm against water.