Blood tests are prescribed to refine the diagnosis of certain diseases. Here are some guidelines for the proper conduct of your blood test, and to better understand the results communicated by the laboratory.
WHAT IS A BLOOD TEST?
A blood test is a blood sample taken from a vein, most often in the arm, using a needle. It allows the blood to be analyzed to diagnose certain diseases.
This examination is not very painful. However, the skin may be slightly sensitive when the needle passes through it. Also, in children, an anesthetic patch is sometimes used to numb the puncture area. It is placed on the arm one hour before the sample is taken.
BEFORE THE BLOOD TEST: TIPS FOR PREPARING WELL
When making an appointment at a blood testing laboratory, ask your contact if you need to be fasting at the time of the blood test.
If you must fast, consider:
- do not eat or drink sugary drinks (except water) in the 12 hours before the blood test;
- avoid smoke and to practice intense physical activity just before the appointment.
Many medications can affect the results of some tests. Also, mention all the treatments you are taking (prescription or non-prescription):
- to the doctor who prescribes the examination;
- to the technician or nurse who performs it.
Furthermore, if you are unable to travel for medical reasons, you can request a home sample.
Still in the same lab?
For the same blood test, the results may vary slightly from one laboratory to another. This phenomenon is due to the use of different dosage techniques. Also, in order to be able to compare the evolution of the dosages, it is preferable to carry out all your blood tests in the same laboratory.
THE PROCEDURE OF THE BLOOD TEST
The day you go to the laboratory, bring your prescription and your papers (Vitale cards and mutual insurance).
The collection takes place in several stages:
- The person who greets you checks your identity, your prescription and that you are fasting if this is useful.
- You are taken to a box or small room, where you are seated in an armchair.
- The technician prepares the tube(s) that he will use to collect your blood (most often, several are necessary).
- He will put a tourniquet on you (a tight tie above the elbow, temporarily blocking blood flow, to facilitate the collection).
- The blood sample is taken from a vein, often on the inside of the elbow, with a single-use needle. The different tubes are positioned successively on the needle, which remains in place in the vein.
- The technician removes the tourniquet and then the needle.
- He puts on a pressure bandage to prevent a hematoma from forming. You press on the bandage yourself for one to two minutes (or more, in the case of clotting disorders).
- The technician labels the tubes with your name and tells you how long it will take to get your results.
- The medical biologist validates and interprets the results.
- The results are transmitted to the prescribing physician.
What do the reference values (RV) mentioned in the blood test results correspond to?
THE reference values The following are standards of results, varying according to the assay techniques used, gender and age. They are generally listed on the right side of the document.
If your results do not fall within these norms, inform your doctor, who will provide you with explanations.
A figure above or below the set limits does not systematically indicate an illness.
UNDERSTANDING BLOOD GLUCOSE TEST RESULTS
The blood sugar is the assessment of the concentration of glucose (the body’s main source of energy) in the blood.
It can reveal:
- a glucose level that is too low compared to the reference value (hypoglycemia);
- too high a glucose level (hyperglycemia, characteristic of diabetes). Diabetes is diagnosed when fasting blood sugar is equal to or greater than 1.26 g/l (or 7 mmol/l), a level observed on 2 occasions.
Blood sugar is often measured both fasting and after meals (postprandial blood glucose measurement).
The doctor may also order an oral glucose tolerance test (HGPO). This analysis is based on an initial blood sample taken on an empty stomach. Several other blood samples are then taken at regular intervals after drinking a liquid containing a known quantity of glucose. This test may be prescribed, for example, when the doctor or midwife suspects a gestational diabetes in a pregnant woman.
UNDERSTANDING BLOOD LIPID TESTING RESULTS
The blood lipid profilealso called exploration of a lipid anomaly (EAL), aims to measure the amounts of the two main types of lipids (fats) in the blood.
Cholesterol
It is mainly produced by the liver, and also provided by food. Its dosage concerns three distinct elements:
- The total cholesterol level.
- The LDL-cholestérol (or “bad cholesterol”) carried in the blood to cells. It can be deposited on the walls of the arteries if its level is too high, which increases the cardiovascular risk.
- The HDL-cholesterol : it collects excess “bad cholesterol” in the blood, to bring it to the liver which ensures its elimination. This “good cholesterol” therefore exerts a protective effect on the body, especially if its quantity is high.
Triglycerides
They are provided by food. They are stored in so-called adipose cells, to serve as an energy reserve for the body.
Recommended rates
Recommended levels for LDL cholesterol and triglycerides differ for each patient, depending on their cardiovascular risk factors. In the absence of cardiovascular risk factors, the following levels are considered normal:
- a total cholesterol level of less than 2 g/l;
- an LDL cholesterol level of less than 1.6 g/l;
- an HDL cholesterol level greater than 0.4 g/l;
- a triglyceride level of less than 1.5 g/l.
Furthermore, the lipid profile considers the appearance of blood serum (liquid from the blood, after removal of blood cells and proteins participating in coagulation). Normally clear, it can also be opalescent or milky (which sometimes reveals an excess of triglycerides).
L’hypercholesterolemiamixed dyslipidemia (increased cholesterol and triglycerides) and certain hypertriglyceridemias constitute major risk factors for atherosclerosis (formation of atheroma plaques) involved in the occurrence of cardiovascular diseases:
*This content may be written by:
- Doctor Laurence Rinuy, medical advisor to Health Insurance,
- Doctor Myriam Boivin, medical advisor to Health Insurance,
- or Doctor Jean-François Laurent, pharmacist advisor to Health Insurance.