Medications Can Interfere with Lab Results

Many medicines, including prescription drugs, over-the-counter products, and supplements, can change the results of lab tests.

These changes can make it seem like something is wrong when it isn’t, or hide a real problem. Up to 4 in 10 people who have blood tests may have their results affected by their medications.

Some drugs change lab results because of how they work in the body—for example, stomach acid medicines (PPIs) can raise a test marker called chromogranin A, and thyroid medications lower thyroid-stimulating hormone (TSH).

Others cause false readings by reacting with the testing chemicals, such as high-dose vitamin C, which can cause a falsely high blood sugar reading, or certain antibiotics, which can make kidney tests look abnormal.

Because of this, it’s important to tell your doctor and the lab about all medicines, vitamins, and supplements you take, especially within the last 10 days before a test.

This helps avoid wrong results, unnecessary stress, or incorrect treatment.

Optimal Takeaways

• Medicines, supplements, and vitamins can change lab test results.
• Some drugs cause real changes in body chemistry; others interfere with test machines or chemicals.
• Common examples include stomach acid medicines, antibiotics, vitamin C, and cholesterol drugs.
• Always tell your provider and lab staff about anything you’ve taken in the past 10 days.
• Clear communication prevents false results and helps providers give the right diagnosis and treatment.

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