Everything You Need to Know About Blood Tests

What is a Blood Test?

A blood test is any test that involves the collection and analysis of blood samples taken from a patient. Your doctor will let you know when you need to get a blood test but as you age you will probably be required to get a blood test at least once a year.

When a blood test is required, the doctor will give you a referral for a pathology practice. Sometimes that practice will be attached to the clinic you are in (as is often the case with medical centres)  or may be a standalone pathology clinic. 

Unlike a normal referral, the doctor doesn’t refer you to a specific pathology centre but rather to a pathology company that runs a chain of pathology centres, allowing you to have your test performed at a place most convenient for you.

Blood tests can check a number of different factors. Depending on what is being examined, a blood test is categorised in one of two ways:

  • Fasting - a fasting blood test requires the patient to fast for around eight to 12 hours before blood is taken so that no variables may skew the results. Nothing to eat or drink, except water, should be had before the test. Some tests may also require abstaining from certain medications or activities as well before blood is taken.Fasting tests check for things like blood glucose levels, lipids, vitamin B-12, iron or a metabolic panel.
  • Non-fasting - a non-fasting blood test may be performed at any time. Non-fasting tests for a number of things including triglycerides, lipids (the variation between fasting and non-fasting results appear minimal), calcium, cardiac enzymes, C-reactive protein and a full blood count.

How is a Blood Test Performed?

When you present for a blood test at a pathology clinic you will first have your details checked and then asked to take a seat. A tourniquet will be fastened around your upper arm to help the attending nurse find a suitable vein to draw blood from. In some cases the nurse may not be able to find a viable vein in the crook of your arm and may instead look for an alternative site to draw blood, such as the back of the hand.

Once a vein has been identified, the pathology nurse will insert a needle attached to a cannula. A cannula is a long tube with a trocar (needle) at one end and an attachment at the other that allows blood to be drawn into vials. There may be a slight pinch when the needle is inserted, but having blood drawn should not hurt. 

Drinking plenty of water a few hours before you have blood drawn may make it easier for a nurse to find a vein as well as make the process of drawing blood smooth and easy. One or more vials of blood are drawn to be sent to a lab for testing. 

Once the blood has been drawn, the nurse will remove the cannula and you will be advised to keep pressure on the puncture site for a short while before a plaster is placed over the site. You will also be advised not to overuse the arm for the rest of the day (heavy lifting, etc).

Before you leave, the pathology nurse will again check your details to confirm that the vials are correctly marked. They will then be sent to a pathology clinic for testing. Your doctor will typically receive the results within a few days.  

What May Be Tested For?

A number of factors may be studied with a blood test to diagnose disease, investigate possible reasons for symptoms the patient may be experiencing, or simply monitor overall health. When a doctor orders a blood test they may want to test a single factor (such as blood glucose levels) or a number of different factors simultaneously.

Factors that may be tested for in blood include:

Calcium - non-fasting

If you are experiencing symptoms including weakness, loss of appetite, fatigue, excess thirst or abdominal pain, your doctor may order a calcium blood test. Calcium testing is part of the screening process for kidney disease, kidney stones, some cancers, nutritional deficiencies and thyroid disease.

Cardiac Enzymes - non-fasting

A cardiac enzyme test looks for the presence of enzymes (such as troponin) that are released when the heart muscle is damaged. Presence of troponin may indicate heart damage or that a person has had a heart attack.

Cholesterol and Lipids - fasting

This test measures the amount of various fats and cholesterols in the blood. The test looks at HDL (good cholesterol), LDL (bad cholesterol) and triglycerides. This test may be ordered to assess risk of heart disease or other complications, especially for people over 45 or living with diabetes.

If you need to schedule an appointment with a doctor to get a blood test, the fastest and easiest way to search for and book medical appointments online is through MyHealth1st.

C-Reactive Protein (CRP) - non-fasting

C-reactive protein production is increased when infection or inflammation is present in the body. The test is used to gauge the severity of infection or inflammation and may be used to test for suspected inflammatory diseases such as IDB (Inflammatory Bowel Disease) or Rheumatoid Arthritis . D-dimer - non-fasting

D-dimer is a protein created to help break down blood clots. Typically the levels of D-dime in the blood are extremely low or non-existent. Presence of D-dimer may indicate the presence of blood clots.

Erythrocyte Sedimentation Rate (ESR) - non-fasting

An ESR test looks for the presence of inflammation in the body. ESR is a non-specific test, so while it may prove the presence of inflammation it cannot pinpoint the location or cause of the inflammation. That said, it is one of the key ways in which two diseases, Giant Cell Arteritis and Polymyalgia Rheumatica are diagnosed.

Folate - fasting

A test to see if you have adequate levels of folate in your blood. Folate is one of the essential nutrients required for creating red blood cells and repairing cell and nerve damage. A folate test may be ordered to discover if low folate levels may be the cause of anaemia, or to monitor levels in patients with conditions such as Crohn’s Disease or Cystic Fibrosis.

Full Blood Count (FBC) - non-fasting

Sometimes referred to as a Complete Blood Count (CBC), this is a common blood test that examines the number, size and health of the different blood cells - red blood cells that carry oxygen, white blood cells that fight infection and platelets that cause blood to clot - as well a haemoglobin. The test may be ordered as a general overview of blood health or to help diagnose underlying health issues such as infection, anaemia or exposure to toxins.

Glucose - fasting

Examines the level of glucose in the blood (blood sugar). They are typically used to monitor blood sugar levels in people living with diabetes to ensure that medication and diet are effectively managing glucose levels, or to gauge risk of developing diabetes

Another glucose test, known as an Oral Glucose Tolerance Test (OGTT) is used to see how efficiently you metabolise glucose. This fasting test sees blood being taken twice. 

You first have blood taken when you come in. After the first bloods are drawn you are given a glucose drink and are made to wait for an hour. A second round of bloods are then taken.  

HbA1c - fasting

A test to monitor the management of or diagnose diabetes. The HbA1c test differs from a blood glucose test in that rather than looking at glucose in the blood it instead tests for the presence and amount of “glycated” haemoglobin. The amount of HbA1c formed is in direct relation to the amount of glucose in the blood. hCG - non-fasting

The test looks for the presence of human chorionic gonadotropin, a hormone that indicates pregnancy. hGC may be tested in urine or blood, but the blood test is more sensitive and may detect pregnancy around a week after conception.

International Normalised Ratio (INR) - non-fasting

This test determines the amount of time it takes for blood to clot. It is typically ordered to monitor the effectiveness of anticoagulants (blood thinners), or to test for clotting problems.

Iron - fasting

Tests levels of iron in the blood and other cells, as both high levels of iron and low levels of iron can be dangerous. May be used to test for conditions such as haemochromatosis or anaemia. 

Kidney Function - non-fasting

A kidney function test, also referred to as a renal function test, looks for the presence or levels of creatine, urea and electrolytes (typically chloride potassium and sodium) in the blood. Abnormal levels may indicate kidney disease or damage. Kidney function tests are recommended for people with high blood pressure , diabetes , heart disease or other risk factors for kidney disease.

Liver Function (LFT) - non-fasting

A liver function test looks for the presence of a number of enzymes and proteins in the blood that are produced by the liver, either naturally or when the cells of the liver are damaged. Levels of these substances may show how effectively the liver is working or if the liver is damaged. 

Liver function tests are often ordered for people with liver damage to monitor liver function, heavy drinkers, people with hepatitis , drug users or people with a family history of liver disease.

Magnesium - non-fasting

Examines levels of magnesium in the blood. Magnesium is a vital nutrient and is present in every cell. Most magnesium comes from diet. A doctor may order magnesium tested if you are a heavy drinker, diabetic, have an eating disorder, kidney damage or some other condition that may cause issues with absorbing magnesium.

Oestrogen - non-fasting

An oestrogen test examines the levels of three forms of oestrogen - oestradiol, oestriol, oestrone. The test may be ordered to diagnose reasons for an abnormal menstrual cycle or heavy bleeding, infertility, or hormone imbalances.

Prostate Specific Antigen (PSA) - non-fasting

The PSA test may detect the presence of prostate cancer or monitor its progress. Although the test can diagnose cancer, the antigens aren’t cancer specific, so other conditions affecting the prostate may also cause an abnormal reading.

Testosterone - fasting

A testosterone test looks at the levels of testosterone in the blood of both men and women. A test may be ordered for men experiencing erectile dysfunction or low sex drive, and abnormal levels may be an indicator of infertility in both men and women.

Thyroid Function - non-fasting

The thyroid gland helps regulate the body’s metabolic system, such as heart rate, blood pressure and weight. High or low thyroid readings may indicate an overactive thyroid (hyperthyroidism), an underactive thyroid (hypothyroidism) or pituitary gland damage. 

Vitamin B-12 - fasting

B-12 tests are often rendered in conjunction with a folate test as vitamin B-12 is another nutrient vital for the formation of red blood cells and for cell repair.

Vitamin D - non-fasting

Vitamin D helps prevent a number of diseases and is also responsible for maintaining strong, healthy bones. Your doctor will order a vitamin D test if they believe you may be at risk of vitamin D deficiency due to lack of sun exposure, poor or limited diet or other risk factors.

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