M At The Doctor

The blood test

A blood test makes it possible to measure and analyze compounds present in the blood. Sometimes it is necessary to perform this blood test on an empty stomach.

What can be measured in a blood test?


The cells normally present in the blood can be analyzed. We will calculate their number: red blood cells, white blood cells, platelets.

These blood cells may be normal, too high or too low. The doctor prescribes a blood count (NFS).

One can also possibly find abnormal blood cells, as in some lymphomas or leukemias.

In the case of pregnancy, fetal cells can now be recovered in the maternal bloodstream and their rhesus group, or their chromosomes, analyzed.

One normally finds in the results of a blood test:

  • White blood cells: between 3, 000 and 10, 000 leukocytes / mm3 (or ml). We detail the distribution of the different families of white blood cells (granulocytes 50-70%, lymphocytes 10-30%, oesinophils, monocytes ...). In case of blood pathology abnormal white blood cells can be detected.
  • Red blood cells: between 4.5 and 5.5 million / mm3 (slightly more in men than in women). The analysis is coupled with hemoglobin, the hematocrit. By analyzing certain antigens present on the surface of these cells, we can know the blood group of a person.
  • Platelets: between 150, 000 and 400, 000 / mm3 (or ml).

Biochemical compounds

A blood test will measure and analyze the minerals, oil-elements present in the blood, such as iron, calcium, potassium, sodium, chlorine ... or specific proteins.

It also allows the determination of other more complex compounds, such as uric acid, lactic-dehydrogenase (LDH), gamma-GT, cholesterol, triglycerides, creatinine, amylase, or ferritin.

For example: the normal value of creatinine in the blood: 50 to 110 micromol / l (from 5 to 13 mg / l).

The dosage of these different compounds allows to have good information on the functioning of the kidneys, liver, pancreas ...

This analysis makes it possible to advance a diagnosis. Some compounds are true markers of a pathology, such as an elevation of troponin in case of myocardial infarction.

It is also possible to analyze serum markers, such as tumor markers (cancerous), for example ACE (carcinoembryonic antigen). But also markers of inflammation: VS - CRP.

By a blood test, one can also detect a possible infection (recent or old), by the determination of the antibodies or the antigen of the pathogenic microbial agent, or the microbial agent itself. In the laboratory, one can even analyze which antibiotic is sensitive against the bacteria identified (antibiogram).

A fasting blood test should be performed to measure certain compounds such as blood glucose, cholesterol and triglyceride levels. The doctor specifies on the prescription when the blood test must be performed on an empty stomach. Sometimes blood is taken after absorption of sugar (hyperglycemia caused).

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Read also :

> Ferritin: an iron reserve protein
> Blood groups
> Karyotype: what is it for?
> Other reviews and analyzes

Author: Dr. Nicolas Evrard

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