Blood Tests
A blood test analyses a small sample of your blood to measure cells, chemicals and markers that reflect how your body is working. Common panels include a full blood count, kidney and liver tests, blood glucose and cholesterol. Results are compared against a 'reference range', and should always be interpreted by your doctor.
Overview
What is a blood test?
A blood test analyses a small sample of your blood to measure cells, chemicals and markers that reflect how your body is working. Common panels include a full blood count, kidney and liver tests, blood glucose and cholesterol.
Why are blood tests done?
They are used to screen for or diagnose conditions, to monitor an existing condition or its treatment, and to check that organs such as the liver and kidneys are working — often before a procedure or when starting a new medicine.
Understanding Results
What is a reference range?
Most results are compared against a 'reference range' — the span of values seen in most healthy people. Ranges can vary slightly between laboratories and with your age and sex, and a result a little outside the range is not always a sign of a problem.
Should I interpret my own results?
No. Results should always be interpreted by your doctor, who reads them in the context of your symptoms, history and other tests. A single number rarely tells the whole story.
Results and Follow-Up
What happens if a result is abnormal?
An unexpected value may simply prompt a repeat test, or it may lead to further investigation or a change in treatment. An isolated abnormal value is rarely a cause for immediate alarm — your doctor will explain what it means for you and what, if anything, to do next.
Additional Common Questions
Do I need to fast before a blood test?
It depends on the test. Many blood tests need no fasting, but some — such as certain glucose and cholesterol (lipid) tests — ask you to avoid food and drink (other than water) for a set number of hours. Your clinic will tell you what is required.
What does it mean if a result is outside the normal range?
A result outside the reference range simply means it differs from most healthy people; it does not automatically indicate disease. Many factors can shift results temporarily. Your doctor interprets the value in context and decides whether it needs monitoring or further tests.
How long do blood test results take?
Some results are available within hours, while others — particularly specialised tests — can take several days. Your clinic or hospital can tell you when and how you will receive your results.
Can I rely on online ranges to interpret my results?
Online ranges can help you understand what a test measures, but laboratories use slightly different reference ranges and your results need to be read alongside your overall health. Always confirm what your numbers mean with the clinician who ordered the test.
Sources
This health topic is for general information and is not a substitute for professional medical advice. Always consult a qualified clinician about your individual situation. See our medical disclaimer.