Proteinogram

Definition

Laboratory technique that allows the separation of proteins based on their displacement on a solid support when they are subjected to an electric field. Migration will depend on the weight of the protein as well as its electrical charge. Bands or fractions corresponding to the different types of proteins can be visualized on the solid electrophoresis support.

Proteins are part of key structural and functional substances in the body, such as hormones, hemoglobin, and enzymes. Some are found free in the blood plasma, contributing to the immune defense action and the transport of substances. It is also possible to detect them in other biological fluids but in smaller quantities and in different proportions than plasma.

A first approach to circulating proteins allows classifying them into two groups: albumins and globulins. The term total protein is used to refer to both groups. Albumin is one of the heaviest proteins and is synthesized in the liver. It makes up about 60 percent of total protein. One of the main functions of albumin is to control the osmotic or colloidal pressure, which is the pressure that allows the fluid to be kept within the vascular space and prevents its extravasation. Furthermore, albumin is capable of transporting various substances through plasma such as drugs, hormones or enzymes.

Some globulins are synthesized in the liver, but others, such as immunoglobulins, are synthesized by B lymphocytes, a subtype of white blood cells. Their main functions are the immune defense of the body, although they also participate in the transport of lipids, hormones and minerals such as copper or iron. In turn, by means of electrophoresis globulins can be separated into four groups or fractions:

• alpha-1-globulins: alpha-1-antitrypsin, alpha-1-antichymotrypsin, alpha-1-fetoprotein, and alpha-1-acid glycoprotein.
• alpha-2-globulins: alpha-2-macroglobulin, ceruloplasmin, haptoglobin, and C-reactive protein.
• beta globulins: fibronectin, transferrin, transcobalamin and complement (C3, C4)
• gamma globulins (or immunogammaglobulins): Ig M, Ig A, Ig G and Ig E.

How is the study done?

The proteinogram is usually performed on blood plasma, although it can also be applied to other biological fluids such as urine and cerebrospinal fluid (CSF). A blood sample obtained by simple venipuncture is required to perform a serum proteinogram. When the examination is requested Whether it is a urine proteinogram, 24-hour urine collection will be required in specially designated containers.

To obtain a CSF sample, a lumbar puncture will be performed. The patient should be placed in the lateral decubitus position, with the legs bent over the abdomen and the head bent over the chest. Using a fine needle, it is punctured at the level of the space between the L3-L4 or L4-L5 lumbar vertebrae. It will always be necessary to compare the results of the CSF proteinogram with the results of the plasma proteinogram.

Preparation for the study

No special preparation is required. Although, it is not uncommon, that in addition to the proteinogram, other analytical determinations are requested that may require fasting of the patient.

There are certain drugs that can alter the result of the proteinogram, among which are chlorpromazine, corticosteroids, isoniazid, neomycin, salicylates and sulfa drugs, among others. The withdrawal of the drug should be considered or the practice of the proteinogram should be delayed until the end of the treatment in case of taking these drugs.

What does it feel like during and after the study?

The discomfort during the study is the same that occurs in taking any blood sample. After extraction, there may be slight pain in the area of ​​the puncture, which tends to subside within minutes. Exceptionally, dizziness, nausea or fainting may occur, especially in patients with apprehension about blood draws.

If it is a CSF proteinogram, a lumbar puncture will be performed. In addition to the slight pain in the area of ​​the puncture, cramps can also be felt in both legs at the time of the puncture. After the puncture, absolute rest for 24 hours is recommended to try to avoid the appearance of headache, since it is an adverse effect that, although benign, is very limiting and can last from hours to a few days.

Study risks

Both in the venous blood extraction and in the lumbar puncture a hematoma can occur, which will disappear within 5-10 days. In patients with anticoagulant or antiplatelet treatment, there may be persistent bleeding in the area of ​​the puncture, which will subside by applying pressure to the wound for a few minutes. Lumbar puncture is a safe exploration, but like any invasive technique it is not without risks. Infections (meningitis, cellulitis, spondylodiscitis) are rare when performed under proper sterile conditions. Exceptionally, intracranial hematomas due to excessive CSF evacuation have been described.

Study contraindications

Plasma protein electrophoresis is not recommended in patients with high concentrations of C-reactive protein (CRP). CRP is a protein that occurs regularly in acute infectious or inflammatory processes. When it occurs in high concentrations in blood plasma, it can lead to misinterpretation of the proteinogram.

Contraindications to the practice of the CSF proteinogram are those that contraindicate the performance of lumbar puncture: psychomotor agitation, coagulation disorders, intracranial hypertension and dermatological infection in the area where the puncture should be performed.

There are no contraindications for the urine proteinogram.

Reasons why the study is carried out

The proteinogram is one of the most requested analytical tests due to the clinical information it can offer. Depending on the medical pathology suspected by the doctor, a proteinogram will be requested in plasma, urine or cerebrospinal fluid.

• Plasma. The proteinogram will reflect the excess or deficit of one or more plasma protein fractions. The detected defect can be useful for the diagnosis of inflammatory processes, liver cirrhosis, nephropathies or immunological defects. It is especially useful for the diagnosis and monitoring of monoclonal gammopathies, which are a group of hematological diseases characterized by excessive and abnormal production of an immunoglobulin or part of it.
• Urine. The kidney is in charge of eliminating the waste products of metabolism, so the amount of protein in the urine of a healthy person should be practically nil. In some blood diseases, such as myeloma, there is an excessive production of proteins of the group of globulins, which exceed the renal filtration systems and can appear in urine. Therefore, it will be useful to perform a urine proteinogram if this clinical entity is suspected. A urine proteinogram will also be requested when the presence of kidney disease that favors the loss of urinary proteins is suspected. In both cases, it will always be necessary to compare the results with the serum proteinogram.
• CSF. It is useful for the diagnostic study and follow-up of neurological diseases such as multiple sclerosis or Guillain-Barré disease.