Blood test

A blood test can provide substantial information for the diagnosis and treatment of patients. The goal of the test depends on the requested measurements, the measurement interval and your condition.

Preparation

Some measurements must be done while you are fasting. Your physician will inform you if this is the case.
This means:

• clear liquids (only water, tea, coffee) at least two hours before the test
• light meals and dairy products at least six hours before the test
• normal meals at least eight hours before the test

Test

Blood is usually taken from a vein in the fold of the elbow. In order to see the veins well, a tourniquet will be wrapped around your upper arm. The vein will be pricked and blood will be collected in a small tube.

A blood draw has few associated risks. Local bruising is possible but does not require much looking after.

• Certain cardiac patients preventatively take anticoagulation medication, Vitamin K antagonists. If that is your case, you must inform the nurse before the blood draw.
  The medication dose must be set according to the speed with which the blood coagulates, which can be measured with a blood draw. A dose that is too high thins the blood too much. This means that every bruise can cause serious bleeding or that spontaneous bleeding may occur. A dose that is too low can have an insufficient effect on preventing spontaneous clot formation in the heart, which could lead to stroke. The degree of anticoagulation can be measured with some medication (INR measurement).

Several things can be measured in the blood. A few of these important measurements are discussed below.

NTproBNP test

BNP stands for Brain Natriuretic Peptide. This is a protein. Muscle cells that are in the heart chamber/ventricles secrete this protein if they have been under increased pressure for a long time. An elevated NTproBNP level in the blood is clinical evidence of heart failure. A low NTproBNP level in the blood can rule out heart failure.

Troponin test

Heart muscle cells die when they do not get oxygen during a heart attack. When these dead cells break apart, they release cardiac enzymes. If these enzymes are found in the blood, this means that the heart is damaged. Shortly after a heart attack, the level of cardiac enzymes is at its highest. It then decreases over the course of a few days, more or less in a predicable fashion.

Troponin is a sensitive parameter of heart muscle damage. It is also more specific than other parameters, such as CK (creatine kinase), SGOT (trasnaminase glutamate oxaloacetate), SGPT (transaminase glutamate pyruvate) and LDH (lactate dehydrogenase).

Cholesterol test

Cholesterol is a fat that the body needs as a building block substance. Cholesterol is usually made in our liver (90%). A small amount of cholesterol is consumed in our diet (10%). Cholesterol circulates in our blood in the form of tiny balls.

Cholesterol is divided into LDL and HDL components. LDL cholesterol transports fats from the liver to the body. If the LDL is too high, then there is too much cholesterol in the blood and this can collect on the blood vessel wall. This could lead to constrictions in the arteries.

The LDL (bad cholesterol) level should be low. HDL cholesterol removes the deposited LDL cholesterol from the vessel wall and transports it to the liver. The HDL (good cholesterol) level should be high, since this reduces the risk of contrictions. When the cholesterol level is measured in the blood, the target values are (for primary prevention):

If you have a high risk of cardiac or vascular disease (this is the case for secondary prevention), your physician will set stricter guidelines.

Glucose measurements

Glucose is a sugar that our body needs as a source of energy. Our body makes glucose from dietery carbohydrates. After eating, the glucose level in the blood increases. Insulin ensures that the blood sugar level does not get too high.

In diabetes, the glucose level in the blood is too high.

There are two possible causes:

• Type 1 diabetes: This patient cannot produce any insulin, which means the blood glucose level increased uncontrollably. Type 1 diabetes is seen often in young patients and is treated with insulin injections.
• Type 2 diabetes: This is often seen at an older age (old-age diabetes). With this type of diabetes, insulin is still produced, but reacts less effectively in the body. This problem is often combined with problems of high blood pressure, obesity and elevated cholesterol.

Diabetes is a very important risk factor for coronary disease.

Blood sugar must be measured while you are fasting. This means:

• clear liquids (only water, tea, coffee) at least two hours before the test
• light meals and dairy products at least six hours before the test
• normal meals at least eight hours before the test

The target values are:

In some cases, extra tests must be performed:

• Oral Glucose Tolerance Test (OGTT): This test is an extensive diagnostic test and is performed when a simple blood test shows that there is a possibility of diabetes. The test consists of multiple blood draws at fixed intervals after having consumed a glucose drink.
• HbA1c test: Diabetics have changes in the haemoglobin in the blood. These changes are measured with the HbA1c, which is measure of the blood sugar level over a longer period of time.

Latest publication date: 11/01/2024
Supervising author: Apr. Biol. Baetens Dimitri, Dr Elzo Kraemer Ximena