Blood Tests : A way of investigating and diagnosing health conditions


The blood test, which has numerous uses, is one of the most common types of medical examinations.

A blood test might be used, for instance, to:

  • Examine your overall health
  • Look for infections
  • Check how well your kidneys and liver are working.
  • Have specific hereditary problems screened for.

Most blood tests are performed by a doctor, nurse, or phlebotomist at your general practitioner's office or nearby hospital and only take a few minutes to complete.


The healthcare professional who arranges your blood test will let you know if there are any particular instructions you need to follow before the test.

For instance, based on the kind of blood test, you might be required to:

  • For up to 12 hours, refrain from eating or drinking anything (fasting) besides water. learn more about consuming food and liquids prior to a blood test.
  • Stop taking some medications
  • It is critical to adhere to the directions given to you because failing to do so could impact the test's outcome and necessitate postponing or repeating the procedure.

During a Blood Test

For a blood test, a blood sample is normally taken from an arm blood vessel.

Given that it is quickly exposed, the arm is a useful body component to employ. The usual places to take a sample are the inside of the elbow or wrist, where the veins are relatively close to the surface.

On occasion, blood samples are collected from the back of a child's hand. Before the sample is taken, their skin may be numbed with a specific spray or ointment.

Typically, a tourniquet is wrapped tightly around your upper arm. As a result of the arm being squeezed, the blood flow is momentarily slowed, and the vein enlarges. This facilitates a sample's ability to be easily taken. 

The doctor or nurse may use an antiseptic wipe to clean the skin region before obtaining the sample.

The vein is punctured using a needle that is connected to a syringe or other unique container. A sample of your blood is drawn out using a syringe. As the needle is inserted, you might get a minor pricking or scratching sensation, but it should not hurt. If you are uncomfortable with needles or blood, let the person collecting the sample know so they can help you feel more at ease.

Once the sample has been collected, the tourniquet will be loosened and the needle will be removed. Using a cotton-wool pad, pressure is applied to the skin for a short period of time. You could apply a plaster to keep it clean.

After the Blood Test

Since only a tiny amount of blood is drawn during the test, there should not be any noticeable side effects.

The test can cause some people to feel lightheaded and faint. Inform the person administering the exam if this has ever happened to you so they are aware and can make you feel more at ease.

You can have a tiny bruise where the needle entered after the test. Bruises can hurt, but they are typically not harmful and go away within a few days.

Blood Test Results

Your name and contact information will be written on a bottle into which the blood sample is placed once it has been drawn. Then, depending on what has to be verified, it will be transported to a lab where it will either be viewed under a microscope or subjected to chemical testing.

The hospital or your general practitioner receives the results. Some test results will be ready the same day or a few days later, while others may not be accessible for many weeks. When and how your results will be delivered to you will be communicated to you in advance.

It can occasionally be difficult and disappointing to receive findings. You may decide to bring a dependable friend or relative with you to a test if you are concerned about the results. You will be provided with specialised counselling for some tests, such as HIV testing, to assist you in coping with your results.

Types of Blood Tests

Blood tests can be performed for a variety of purposes, including aiding in the diagnosis of a condition, evaluating the health of specific organs, and checking for particular hereditary abnormalities.

Test for blood cholesterol

Cholesterol is a fatty chemical that is mostly produced by the liver from the fatty foods you consume and is essential for the body's normal operation.

A high cholesterol level can make it more likely for fatal illnesses like heart attacks and strokes to occur.

Blood cholesterol levels can be measured with a fasting blood test. You might be asked to skip meals for 12 hours prior to the test to ensure that all food is thoroughly digested and will not affect the results.

Blood testing

In order to do this, a tiny sample of blood must be drawn from at least one additional portion of your body in addition to a vein in your arm.

In order to encourage bacterial growth, nutrients are added to the samples.This can assist in determining whether your blood contains any microorganisms. Usually, two samples or more are required.

Blood gas analysis

A sample of blood gasses is drawn from an artery, typically at the wrist. Only hospitals perform it, and it is almost certainly uncomfortable.

Using a blood gas test, you may determine how much oxygen and carbon dioxide are in your blood as well as how much acid and alkali are in it (the pH harmony).

A pH imbalance may result from:

  • respiratory issues including pneumonia or chronic obstructive pulmonary disease (COPD)
  • issues with your metabolism (the body's natural processes for converting food into energy), like diabetes, renal disease, or recurrent vomiting

Blood tests for glucose (sugar)

Checking the amount of sugar (glucose) in the blood allows for a number of tests that can be used to diagnose and monitor diabetes.

These consist of the:

  • During a fasting glucose test, your blood sugar level is measured after you've been without food or liquids for at least eight hours. 
  • A glucose tolerance test measures your blood sugar levels when you are not fasting.
  • A test known as the HbA1C is performed in a hospital or GP office to determine your average blood sugar level over the previous three months.
  • There may be kits for testing blood glucose at home. These can be tested with just a tiny "pinprick" of blood.

Blood analysis

This is done to determine your blood group before giving blood or receiving a blood transfusion.

Your immune system may attack the red blood cells if you get blood that does not match your blood group, which could result in potentially fatal problems.

Additionally, blood typing is done while pregnant since there is a slight chance that the unborn child will have a different blood type than the mother.

Your blood will be tested at least once during your pregnancy to see if there's a danger of rhesus disease if you don't already know your blood type.

Injections of a medication that prevents the mother's immune system from attacking her baby's blood cells can be administered if testing indicates there is a risk of rhesus disease. 

Blood testing for cancer

Several blood tests can be performed to help diagnose specific cancers or determine whether you have an increased risk of developing them. risk of getting a specific kind of cancer.

These comprise exams for:

  • Genes that increase your risk of some cancers, such as the BRCA1 and BRCA2 genes, such as certain versions of these genes can greatly increase a woman's risk of developing ovarian cancer. 
  • Prostate-specific antigen (PSA) - this can help diagnose prostate cancer, although it can also detect other issues such as an enlarged prostate or prostatitis. 
  • CA125 protein - although it can potentially be an indication of other conditions, the CA125 protein can signal ovarian cancer.

Chromosome analysis (karyotyping)

This test looks at chromosomal bundles, which are collections of genetic material. It could be feasible to identify genetic problems by counting the chromosomes (each cell should have 23 pairs) and examining their structure.

Chromosome analysis is useful for:

  • assisting in the diagnosis of variations in sex development (DSD), such as androgen insensitivity syndrome for couples who have had numerous miscarriages, in order to determine whether a genetic issue might be to blame.

Testing for coagulation

You could get a coagulation test to see whether your blood clots normally.

If it takes a long time for your blood to clot, it could indicate a bleeding issue such von Willebrand disease or haemophilia.

The international normalised ratio (INR), a specific kind of coagulation test which is used to track the dosage of anticoagulants like warfarin and check

Test for C-reactive protein (CRP)

Another test that aids in the identification of inflammation-causing illnesses is this one.

The liver produces CRP, and a higher-than-normal level of CRP indicates that your body is inflamed.

Electrolyte analysis

A healthy water balance in your body is one of the functions that minerals called electrolytes, which are found in the body and include sodium, potassium, and chloride, carry out.  Electrolyte changes can result from a number of different factors, such as dehydration, diabetes, or certain medications.

Rate of erythrocyte sedimentation (ESR)

The duration it takes for red blood cells to drop to the bottom is how this test operates. It is more likely that there is severe inflammation the faster they fall.

An ESR is frequently used to assist in the diagnosis of diseases linked to inflammation, including:

  • Arthritis
  • Endocarditis
  • Crohn's illness
  • Rheumatic polymyalgia

An ESR can be helpful in determining whether you have an infection in addition to other tests.

The full blood count (FBC) test determines the types and amounts of blood cells in your body, including platelets, white blood cells, and red blood cells.

This can offer important signals about prospective health problems as well as information about your general state of health.

Genetic analysis and inspection

This entails taking a sample of DNA from your blood and looking through it for a certain genetic variation (mutation).

This method can be used to diagnose the following genetic conditions:

  • Cystic fibrosis, which causes a buildup of mucus in the lungs.
  •  Haemophilia, a condition that impairs the blood's ability to clot
  • A disorder characterised by muscle weakness and a progressive loss of movement called spinal muscular atrophy
  • Lack of healthy red blood cells is a symptom of sickle cell disease
  • The disorder known as autosomal dominant polycystic kidney disease induces the development of cysts, which are fluid-filled sacs, in the kidneys
  • The presence of a specific gene that raises a person's risk of acquiring a genetic disorder can also be determined by genetic testing.

Test for liver function

When the liver is harmed, it discharges compounds known as enzymes into the blood and the levels of proteins the liver produces start to decline.

It is feasible to develop an understanding of how well the liver is functioning by examining the amounts of various enzymes and proteins. functioning.

This can aid in the diagnosis of cirrhosis (liver scarring), hepatitis, and liver diseases brought on by alcohol.

Test of thyroid function

Thyroid-stimulating hormone (TSH), thyroxine, and triiodothyronine levels are measured in your blood using this test (thyroid hormones).

You may have a thyroid issue such as an underactive thyroid or an overactive thyroid if you have low or high amounts of these substances.


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Page last reviewed: Mar 13, 2023

Next review due: Mar 13, 2025

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