Blood Tests

Last updated: August 4th, 2020

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Blood tests are the most common type of test because they are used to test a wide range of conditions. This article goes into some common type of tests. But first and foremost, so that you know what to expect, what goes on during a blood test?

How is a blood test done?

The preparation before the test varies on the type of test, and may require the patient to:

  • stop taking a certain medication
  • fast (avoid eating or drinking anything, except water) for up to 12 hours

The test itself involves extracting blood from a blood vessel, for adults usually in the arm. The inside of the elbow (as shown below) or wrist is a convenient because it can be easily uncovered and the veins are relatively close to the surface.

The image below also shows a tightened band around the upper arm. The band squeezes the arm, slowing down the flow of blood which causes the vein to swell. This makes it easier to extract the blood sample:

Extracting blood from the inside of the elbow
Extracting blood from the inside of the elbow.

Right before taking the sample, the area of skin is usually cleaned with an antiseptic wipe to avoid complications. The needle attached to a syringe then goes in causing a pricking sensation. Before removing the syringe, the tight arm band is removed, usually while the last tube to be drawn is filling.

After the needle is removed the patient is instructed to press down on the gauze, applying adequate pressure to avoid bruise formation. Finally plaster is put on the slight bruise to keep it clean.

Finally blood test samples are sent to the lab where the specific tests are conducted.

Common blood tests

Blood samples examined at the lab.
Blood samples examined at the lab.

The list below includes commonly performed blood tests:

Blood cholesterol test. While it has a bad name, cholesterol is a fatty substance actually vital for the normal functioning of the body. The bad name comes from the fact that a high level of bad cholesterol can contribute to an increased risk of serious problems such as heart attacks and strokes. This article explains the ins and outs of good and bad cholesterol.

In order to prevent the test's accuracy being impaired by food currently in the digestive system, the patient might be asked to fast for up to 12 hours before the blood sample is extracted. Luckily, 8 hours of sleep can be put within those 12 hours, resulting in a not so terribly long fast.

Blood sugar, aka "blood glucose" test. These are mainly used to diagnose and monitor diabetes by checking the level of sugar (glucose) in the blood. The type of test depends on how long how the fast before the test is.

Cancer blood tests are carried out to help diagnose certain cancers or check whether the patient is at an increased risk of developing a specific type of cancer. For example, tests:

  • for prostate-specific antigen (PSA) can help diagnose prostate cancer, even though it might indicate other problems such as an enlarged prostate
  • for CA125 protein can indicate ovarian cancer, although it can also be a sign of other things such as pregnancy or pelvic inflammatory disease (PID)
  • for certain versions of BRCA1 and BRCA2 genes can greatly increase a woman's chance of developing breast cancer and ovarian cancer

Coagulation tests may be used to see if the patient's blood clots in the normal way; if the patient's blood takes a long time to clot it may be a sign of a bleeding disorder. A type of coagulation test called the international normalised ratio (INR) is used to monitor the dose of anticoagulants, such as warfarin, and check that the patient's dose is correct.

Electrolyte test. Electrolytes are minerals found in the body that maintain a healthy water balance in the body. These include sodium, potassium and chloride; changes in the level of electrolytes may be caused by dehydration, diabetes or certain medications.

Blood samples for examination.
Blood samples for examination.

A Full blood count (FBC) checks the types and numbers of cells in the patient's blood, including red blood cells, white blood cells and platelets. The result indicates the patient's general health, as well as providing important clues to uncover specific health problems the patient may have.

Liver function test. This measures the levels of enzymes and proteins released by the liver into the blood when it is damaged, drawing a picture of how well the liver is functioning. This test can help diagnose specific liver conditions including hepatitis, cirrhosis (liver scarring), and alcohol-related liver disease.

Thyroid function test. This tests the blood for levels of thyroid and thyroid-stimulating hormones; low or high levels of these hormones might indicated an underactive thyroid or overactive thyroid.

Pharmacies providing blood testing services

Clinics providing blood testing services

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