Medications that can affect blood tests

blood tests 1

If you are experiencing pain, it’s easy to buy co-codamol to alleviate the symptoms. However, if your symptoms do not dissipate over the course of a fortnight, your doctor may book you in for a blood test to diagnose any conditions you may have.

Before undergoing a blood test, it is important to listen to the advice of your doctor. This is because certain medications you take can affect the outcome of the blood test. In some cases, this can cause false-positive results. In other instances, medications could mask an underlying illness.

Your doctor should be able to provide you with information on what foods and drinks to avoid, along with any medications you need to stop taking.

In most cases, you will be able to continue taking your medicines as normal. However, you should be aware that the following drugs can affect blood tests:

Pain relief medicines

Most analgesic medications have the unfortunate side effect of causing potential liver toxicity. The following drugs are known to cause abnormal liver enzyme levels in individuals who use them directly prior to providing a blood sample:



Antibiotics don’t always affect the results of blood tests to the degree where the doctor will not be able to find what they’re looking for, unless they are prescribed at particularly high concentrations. It is also worth pointing out that if the test is specifically being undertaken to determine levels of bacteria in the blood (to identify an infection, for example) then antibiotics will almost certainly influence bacteria levels and strengths.

The following classes of antibiotic can affect blood work results:


Cholesterol-lowering drugs

Medications designed to lower cholesterol, such as statins, can affect the liver. It is therefore not uncommon for patients who regularly use statins to receive blood test results which indicate that their liver is not functioning properly.

Cardiovascular medications

Because medications for heart disease are often prescribed to thin the blood, block certain receptors and prevent blood from coagulating, it is not uncommon to for cardio patients to receive skewed results.

Patients who are taking any medications should ensure that their healthcare providers are aware of their current drug regimen. In many cases, a doctor will be able to adjust the results of a blood test to account for the changes made by temporary or long-term medication use.

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