Blood Groups: What are they? Types, Tests, Associated Conditions and Recommendations

Red blood cells have specific proteins on their surface, called antigens. In addition, its plasma contains antibodies that will attack specific antigens if they are present.

ABO and rhesus are both types of antigens found on the surface of red blood cells. There are many other types, but these are the most important.

ABO blood types

These were the first discovered type:

  • If you have type A antigens on the surface of your red blood cells, you also have anti-B antibodies in your plasma.
  • If you have type B antigens on the surface of your red blood cells, you also have anti-A antibodies in your plasma.
  • If you have type A and type B antigens on the surface of your red blood cells, you have no antibodies to the A or B antigens in your plasma.
  • If you do not have type A or type B antigens on the surface of your red blood cells, you have anti-A and anti-B antibodies in your plasma.
  • It is not known what the functions of antigens A and B are. People who have none (blood group O) are just as healthy.
  • There is some evidence that people of different blood groups may be more or less susceptible to certain diseases, for example, blood clots in the blood vessels ( thromboembolism ) and malaria.
  • There is no evidence that people with different blood groups should follow other diets.

Tipos Rhesus

Most people are ‘rhesus positive. This means that they have rhesus antigens in their red blood cells. But, about 3 out of 20 people do not have rhesus antibodies and are said to be “rhesus negative.”

Names of blood groups

Your blood group depends on which antigens are on the surface of your red blood cells. Their genetic makeup, which they inherit from their parents, determines which antigens are present in their red blood cells.

It is said that your blood group is:

  • A + (A positive) if it has A and Rhesus antigens.
  • A- (A negative) if it has antigens A but does not have rhesus antigens.
  • B + (B positive) if it has B and Rhesus antigens.
  • B- (B negative) if it has B antigens but does not have rhesus antigens.
  • AB + (AB positive) if it has antigens A, B and rhesus.
  • AB- (AB negative) if it has antigens A and B but does not have rhesus antigens.
  • O + (O positive) if you do not have antigens A or B, but you have rhesus antigens.
  • O- (or negative) if it does not have antigens A, B or rhesus.

Other types of blood

Many other types of antigens can appear on the surface of red blood cells. However, most are classified as ‘secondary’ and are not as crucial as ABO and rhesus.


How are blood group tests done?

A blood sample is mixed with different plasma samples known to contain different antibodies.

For example, if the plasma containing anti-A antibodies causes the red blood cells in your blood (erythrocytes) to clump together, you have antigens A in your blood cells.

Or, if the plasma that contains rhesus antibodies causes the red blood cells in your blood to clump together, you have rhesus antigens in your blood cells.

Doing such tests makes it possible to determine which antigens the red blood cells have and choose their blood group.

The routine blood group checks your ABO and rhesus status. Other red blood cell antigens are tested in different situations.

Blood transfusions and cross-matching

If you have a blood transfusion, your blood must be well matched (compatible) with your blood.

For example, suppose you receive blood from a positive and B positive person. In that case, the anti-A antibodies in your plasma will attack the donated blood’s red blood cells (erythrocytes).

This causes the red blood cells in the donated blood to clump together. This can cause a severe or even fatal reaction in your body.

Therefore, before carrying out a blood transfusion, a blood bag from the donor with the same ABO and rhesus blood group as you is selected.

Then, to ensure no incompatibility, a small blood sample is mixed with a small piece of blood from the donor.

After a short time, the mixed blood is examined under a microscope to see if there has been agglutination of blood. If there is no agglutination, it is safe to transfuse the blood.

Blood groups and pregnancy

A blood group test is always performed on pregnant women. If the mother has negative rhesus and the fetus is positive (inherited from a positive rhesus parent), then the mother’s immune system can produce anti-rhesus antibodies.

These can attack and destroy the baby’s blood cells. This is rarely a problem in a first pregnancy.

However, without treatment, this can become a severe problem in later pregnancies since the mother’s immune system will be ‘sensitized’ after the first pregnancy.

Inflammation and blood proteins

If you have inflammation in one part of your body, additional protein is often released from the site of inflammation and circulates in the bloodstream.

The globular sedimentation rate (ESR), the C-reactive protein (CRP), and the plasma viscosity (PV) are commonly used to detect this protein increase. In this way, they are used as inflammation markers.

Erythrocyte sedimentation rate, C-reactive protein, and blood analysis with plasma viscosity

Blood analysis of erythrocyte sedimentation rate or ESR (for its acronym in English)

A blood sample is taken and placed in a tube containing a chemical to prevent the blood from clotting. The line is left in a vertical position. The red blood cells (erythrocytes) fall gradually to the bottom of the tube (like sediment).

The clear liquid plasma is left at the top. The ESR measures the rate at which the red blood cells separate from the plasma and fall to the bottom of a test tube. The speed is measured in millimeters per hour (mm / h).

This is easy to measure since there will be several millimeters of clear liquid in the upper part of the red blood after one hour.

If specific proteins cover the red blood cells, they will stick together and cause the red blood cells to fall more quickly. So, a high ESR indicates that you have some inflammation somewhere in the body.

ESR levels are generally higher in women. Also, the level increases with increasing age.

Blood test C-reactive protein or CRP (for its acronym in English)

This is sometimes called acute-phase protein. This means that CRP level increases when you have certain diseases that cause inflammation.

CRP can be measured in a blood sample. The CRP test measures the level of a specific protein, while the ESR takes many proteins into account.

The viscosity of plasma or PV (for its acronym in English)

The conditions that the PV test can also control the ESR test monitors. It is another marker of inflammation. However, it is more challenging to perform and is not as widely used as ESR tests.

What conditions affect the erythrocyte sedimentation rate and the C-reactive protein level?

High levels of ESR, CRP, and PV are markers of inflammation. In general, PV and ESR do not change as fast as PCR, either at the beginning of the rash or when it disappears.

PCR is not affected by so many other factors such as PV or ESR, making it a better marker of some types of inflammation.

However, PV is more sensitive and more specific than ESR or CRP when monitoring the activity of rheumatoid arthritis.

ESR, CRP, and PV can increase in many inflammatory conditions, for example:

  • Certain infections (mainly bacterial infections).
  • Abscesses
  • Rheumatoid arthritis.
  • Other muscles and connective tissue disorders include polymyalgia rheumatic, giant cell arteritis, or systemic lupus erythematosus.
  • Injured tissue and burns.
  • Some types of cancer, such as myeloma and Hodgkin’s lymphoma.
  • Crohn’s disease.
  • Rejection of an organ transplant.
  • After the operations.
  • Some conditions reduce ESR, for example, heart failure, polycythemia, and sickle cell anemia.
  • It is also reduced in situations where your body has lower protein levels, for example, in some liver or kidney diseases.

When are these tests used?

To help diagnose diseases.

ESR, CRP, and PV are non-specific tests. In other words, a high level means that ‘something is happening, but more tests will be needed to clarify exactly what that is.

For example, you may be indisposed, but the cause may not be clear. An increase in ESR, CRP, and PV may indicate that there may be an inflammatory condition. This can induce the doctor to perform more tests to find the cause.

It is impossible to diagnose a particular condition only from a high ESR, CRP, or PV level.

However, before more tests are done, your doctor may suggest that you repeat the ESR, CRP, or PV test after several weeks or months.

If it has arisen from a recent infection (a prevalent cause), it is likely to return to normal when your condition improves. You would not need more tests.

Recommendations to control the activity of certain diseases

For example, if you have polymyalgia rheumatica, the disease’s amount of inflammation and activity can be partially assessed by measuring blood tests. As a rule, the higher the level, the more active the disease.

The response to treatment can also be controlled since the level of ESR, CRP, and PV can decrease if the condition responds well to treatment.

The three tests are helpful. However, changes in the CRP are faster. So, for example, a fall in the CRP within a few days of starting treatment for certain conditions is a helpful way to know that the treatment is working.

This may be important to know when a severe infection or a severe outbreak of an inflammatory condition is treated. For example, if the level of CRP does not decrease, it may indicate that the treatment is not working and may induce a doctor to switch to a different treatment.