Learn how to interpret blood test results and understand reference values. Find out what your results may indicate.

Blood tests are often part of a routine health check and, in some cases, can help identify the cause of certain symptoms. Knowing how to interpret blood test results can therefore support the diagnosis of potential health issues.

However, blood test results are not definitive diagnoses. An abnormal result does not necessarily mean that there is a serious health condition.

In this article, we help you understand the meaning of laboratory results according to the different types of clinical blood tests.

Some tests, such as a complete blood count, analyse several different elements in the blood at the same time, while other blood tests check very specific elements.

Depending on a person’s symptoms, health condition and any medication they may be taking, the most common types of clinical blood tests include:

• Complete blood count: measures the number of blood cells, such as red blood cells and white blood cells, to check for issues such as iron-deficiency anaemia.

• Blood glucose test: measures blood sugar, or glucose, levels to check for or monitor diabetes.

• Kidney profile: assesses whether the amount of certain substances in the blood may be causing the symptoms reported by the patient.

• Lipid profile: measures cholesterol levels to assess the risk of developing conditions such as cardiovascular disease and stroke.

• Liver profile: measures the levels of liver enzymes.

In general, blood tests carried out in hospitals are considered “urgent”. For this reason, results are made available to the medical team within a few hours.

Most blood tests carried out at a healthcare unit are routine tests. In these cases, results may take a few days to become available.

Reference ranges for blood, urine, faeces and other fluids vary according to several factors, including demographic data from the healthy population.

In adults, reference values may be expressed using conventional units or the International System of Units, also known as SI units. These ranges differ only in the unit used to express the same laboratory parameter.

The aim is to standardise measurements, not to change clinical test results. Below are some conventional reference ranges to consider when reading your values:

To interpret a complete blood count, for example, you should refer to the reference values in the previous table and consider the following:

• Red blood cells, haemoglobin and haematocrit: the results of these three parameters are related. Values below the normal range may be a sign of anaemia, whose symptoms can include weakness or tiredness. A red blood cell count above the reference values may indicate a medical condition, such as heart disease or haematological diseases including leukaemia, lymphoma or myeloma.

• White blood cells: a low white blood cell count can have several causes, ranging from bone marrow problems to autoimmune diseases, as well as certain medications. A count above the reference values may be due to infection or inflammation. It may also indicate a reaction to medication or intense exercise, an immune system disorder or a bone marrow disease.

• Platelets: both a platelet count below the reference values, known as thrombocytopenia, and above these values, known as thrombocytosis, may be signs of a medical condition or side effects of medication. A platelet count outside the reference range will likely require additional tests to diagnose the cause.

It is important to highlight that blood test results should be correctly interpreted by healthcare professionals.

Not all types of clinical blood tests provide complete answers for a diagnosis, as they do not always require immediate medical follow-up.

In these cases, in addition to blood tests, the healthcare professional will analyse the results of other complementary exams.

Blood test results that fall outside the reference values may not be concerning for a healthy person with no symptoms of disease. In these situations, follow-up may not be necessary.

In general, blood tests are carried out to check how the body responds to injuries, diseases, inflammation, infections and some types of medication.

In addition, the scheduling of blood tests depends on the person’s overall health status.

Most healthcare professionals recommend annual physical exams, which may include a complete blood count. Regular blood glucose tests may also be recommended for people who are overweight or obese.

Although you may interpret your blood test results on your own at first, you should always consult your doctor to check whether additional tests are needed depending on the results.

From common screenings, such as blood tests during pregnancy, to dedicated blood collection rooms for children, Unilabs performs more than 70,000 tests per day, with an average waiting time of 15 minutes.

If you have not had blood tests for some time, schedule your sample collection through the Saúde Unilabs app and check your overall health status.

• Cleveland Clinic (2022). Blood Tests. Available here.

• NHS (2023). Blood tests. Available here.

• British Heart Foundation. Blood tests: how do they work and what do they show? Available here.

• Mayo Clinic (2023). Complete blood count (CBC) - About. Available here.

• MSD Manual - Professional Version (2024). Normal laboratory values. Available here.

• ACSS. Laboratory reference values for adults. Available here.