Understanding Your Blood Tests: What the Common Ones Mean

Blood tests give your doctor a measured look inside the body that an examination alone cannot give. They do three jobs: they check health in someone with no symptoms, they help find the cause of symptoms, and they follow a known condition or its treatment.

Blood carries cells, salts, sugars, fats, hormones and waste products. A change in any of them can point to a problem in an organ such as the liver, kidneys or thyroid, or in the blood itself.

Some tests are routine, such as a complete blood count. Others are chosen for a question, such as a thyroid test for tiredness or an HbA1c test for diabetes.

A single result seldom gives a diagnosis. Doctors read it with your symptoms, your examination, your medicines and your earlier reports. A trend over several tests is often more useful than one number.

Ask your doctor or the pathology lab whether you need to fast, because it depends on the test. Fasting means no food or drink except plain water, usually overnight. Fasting sugar tests usually need it, and cholesterol tests sometimes do. A blood count and thyroid tests usually do not.

• Drink plain water. It does not break a fast, and it makes the blood easier to draw.
• Do not stop any medicine before the test unless your doctor tells you to. Tell the lab what you take, including supplements, because a few can change results.
• Wear a top with sleeves that roll up easily.
• Bring your prescription and earlier reports, so the results can be compared.

If travelling is hard, ask whether home sample collection is possible. It is offered for selected tests in selected parts of Lucknow, and availability is confirmed when you ask. The home visit page explains how to request it.

These are the groups people meet most often. Each answers a different question, and your doctor chooses the ones that fit yours.

Doctors sometimes order a set that combines several chemistry tests, such as sugar, kidney and liver tests with blood salts, called a metabolic panel. Other tests, such as iron, vitamin B12 and hormone tests, are chosen for specific questions.

Here is what a high or low result on four common tests may point to. Only your doctor can say what it means for you.

• Blood count. A low haemoglobin means anaemia, which can cause tiredness and breathlessness. A raised white cell count often points to infection or inflammation. A low platelet count can raise the chance of bleeding.
• Sugar and HbA1c. A fasting sugar shows glucose after a night without food. HbA1c shows your average over weeks, so yesterday's meal does not change it. Both help find diabetes and prediabetes, a stage when sugar is above normal but below the diabetes range.
• Lipid profile. LDL is the cholesterol that can build up in artery walls. HDL is the type that helps clear it. Triglycerides are another fat, raised by sugar, alcohol and excess calories.
• Kidney and liver tests. Creatinine and urea rise when the kidneys clear waste poorly. Raised liver enzymes show liver cells under strain, and raised bilirubin can cause jaundice. Neither names the cause.

A report lists each test, your result, its unit and a reference range. The reference range is the span of values found in most healthy people. It can differ between labs, between age groups and between men and women, so compare your result with the range printed on your own report.

A result flagged high or low is not always a disease. Illness, a recent meal, dehydration, medicines, stress and the time of day can all move a value. A result inside the range does not rule out every problem either. Your doctor may repeat a test or add another to be sure.

Please do not decide what a result means from the internet, and do not change a medicine because of a number. Take the report to the doctor who ordered it and ask three questions:

• What does this result mean for me?
• Does it need a repeat test or another test?
• What should I change, and when should we check again?

There is no single schedule. Your doctor decides, using your age, family history, weight and any conditions or medicines. A healthy young adult may need few tests, while someone with diabetes, thyroid disease or kidney disease needs them at set intervals.

Regular check-ups can find problems before they cause symptoms, such as raised sugar, raised cholesterol or a low haemoglobin. A test helps only if the result is followed up, so keep the report and bring it to your next visit.

A health package groups related tests, usually with a scan or an ECG. It makes sense when your doctor's question matches the package, and not as a screen for everything. The health packages page lets you compare them.

Your doctor decides which tests you need. Bring your prescription, and the team will confirm the tests and how to prepare.