Overview
Blood tests are laboratory tests done on a sample of your blood. They are used for many reasons, including routine health checks, screening for certain conditions, helping diagnose symptoms, and monitoring ongoing illnesses or medicines. Common examples include a complete blood count, blood sugar tests, cholesterol tests, and tests for liver, kidney, thyroid, or immune system function.
Who Is Affected
People of all ages may need blood tests at some point. They are commonly used in primary care, pregnancy care, emergency care, hospital treatment, and follow-up for chronic conditions. Healthcare professionals may recommend blood tests based on age, symptoms, family history, medicines, or other health risks.
Preparation
Preparation depends on the type of blood test. Some tests need fasting for a certain period, while others can be done at any time of day. You may also be asked about medicines, supplements, recent illness, exercise, or alcohol use because these can affect results. Follow the instructions from your clinic or laboratory carefully.
Diagnosis and Tests
A healthcare worker usually takes blood from a vein in the arm using a small needle, or sometimes from a finger prick. The sample is sent to a laboratory, where it is measured for specific cells, chemicals, proteins, hormones, or markers. Results may come back the same day or take longer, depending on the test. Your healthcare professional will explain what the results mean and whether more testing is needed.
Living With It
If you need repeated blood tests, it can help to keep a record of your results and the reason each test was done. Some people feel worried about needles or results, and it is reasonable to tell the healthcare worker so they can support you. If you have a long-term condition, regular blood tests may be part of checking how well your treatment is working.
When to Seek Medical Care
Contact a healthcare professional if you have questions about how to prepare for a blood test or what your results mean. Seek medical care if you have ongoing symptoms such as unusual tiredness, unexplained weight changes, fever, swelling, easy bruising, or other concerns that may lead to testing. Also ask for medical advice if you have fainted during past blood draws or have a bleeding disorder.
When It May Be an Emergency
Urgent medical care may be needed if you have severe symptoms such as chest pain, trouble breathing, confusion, signs of stroke, severe bleeding, or loss of consciousness. These symptoms should not wait for routine blood testing. In rare cases after a blood draw, get urgent help for severe allergic symptoms, heavy bleeding that does not stop, or fainting with injury.
Questions to Ask a Healthcare Professional
You may want to ask why the test is being done, whether you need to fast, and when results will be ready. It can also help to ask what the results may show, whether medicines or supplements could affect them, and if follow-up tests are needed. If you are nervous about needles, ask what can make the process easier.