Key takeaways:
Some lab tests are better at detecting a disease, while others are better at ruling them out. This can affect how accurate your lab results are.
The accuracy of lab results can be affected by many factors, like testing conditions, testing facilities, and the test itself.
While it’s impossible for lab results to be accurate 100% of the time, you can take steps to increase the chances that the results are right.
When you get a clinical lab test, it’s natural to take your results as hard facts. But certain factors can affect the accuracy of the test — like the test manufacturer and what the test is for. Some tests are accurate nearly 100% of the time, while others are well known for being unreliable.
So, before you hang your hat on your lab results, it helps to know the chances that the results may not be accurate. We’re here to break down what goes into testing accuracy and how you can maximize your chances of getting valid results.
How often are lab results wrong?
It’s nearly impossible for a test to be right 100% of the time. And every test has a different accuracy rate. We get more into the factors that affect accuracy below.
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It’s also important to know that calculating accuracy isn’t as straightforward as it may seem. “Accuracy” means how well the test can correctly identify positive and negative cases of a disease or condition. A test with 90% accuracy is expected to be correct in its results 90% of the time.
But it can get complicated. To calculate this accuracy rate, scientists have to consider how often the test gets the positive results correct as well as how often the test gets the negative results correct.
What do negative, positive, and inconclusive test results mean?
A “negative” test result means that you don’t have what the test is looking for. This usually means that your test is normal.
A “positive” test result means that you have what the test is looking for. This usually means you have the disease or condition the test is designed to detect.
An inconclusive test can mean a few different things. It can mean that:
The result is right on the borderline of what is normal or abnormal. So it’s unclear if the test is positive or negative.
The test couldn’t be run on the provided sample. Or the quality of the sample was too low to accurately run the test.
Even though the test result is clear, it’s uncertain if this means you have or don’t have a condition based on context. For example, some tests might look positive. But it only means you have the disease if other conditions are met, like the presence of certain signs or symptoms.
False positives vs. false negatives in lab results
When it comes to “false positives” and “false negatives,” lab accuracy can be a bit more complex than meets the eye. But it’s an important part of understanding what your lab results mean.
False positives
A “false positive” is when a lab result says you have something — or something is present — when you don’t actually have it. For example, a false positive is when a pregnancy test reports that you’re pregnant but you aren’t actually pregnant.
How often a test makes this mistake has to do with how well the test can correctly identify negative cases. If it’s not good at sensing that you don’t have the condition of interest, it’s more likely to tell you that you have the condition when you don’t. This is the “specificity” of a test.
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If the specificity for a test is 90%, that means that out of 100 people who are truly negative, it will correctly identify 90 of them as negative. And 10 of them will get a false-positive result.
False negatives
A “false negative” is a negative result when you actually have a condition or disease. Here’s an example of a false-negative result: You test negative on a rapid COVID antibody test, but you actually have COVID.
If a test isn’t good at sensing if you have the condition of interest, it’s more likely to tell you that you do not have the condition when you actually have the condition. This is the “sensitivity” of a test.
If the sensitivity for a test is 90%, that means that out of 100 people who are truly positive, it will correctly identify 90 of them. Flu tests, for example, have a sensitivity between 50% and 70%. That means that up to 30% to 50% of positive results could be for people who don’t actually have the flu.
Typically, a test is either better at catching positives or at catching negatives. A manufacturer usually can’t increase the sensitivity of a test without decreasing its specificity — and vice versa.
How does disease prevalence affect lab-result accuracy?
How rare (or common) a disease is will also affect how accurate your lab test might be. If the disease is really common, it’s more likely that a positive result will correspond to a person who has the disease. So that means the number of false positives for that test will be lower.
For example, a lab test for high blood pressure — which affects over 30% of the U.S. adult population — will have fewer false positives than a lab test for diabetes — which affects 10% of the U.S. population.
What else can affect your lab results?
Aside from disease prevalence and a test’s sensitivity and specificity, there are several other factors that can affect your test results. These include:
Testing conditions: Results can be affected by where you do the test, like if you can do the test at home or if you have to do it in a doctor’s office or a testing center.
The testing facility: Some labs may use different methods or equipment, and these factors may play a role in how accurate the results are.
Storage and transportation: Incorrect specimen storage and transportation can both affect test accuracy.
Timing: Test results can also be affected by when the test is conducted. The lab test for the flu, for example, is most accurate when it’s done within 3 to 4 days after symptoms first appear. Outside of this window, test results tend to be less accurate.
Food and drink: What you eat and drink can affect some test results. A healthcare professional may ask you to not eat or drink anything for a certain amount of time before a lab test. This is often the case for blood tests.
Certain medications and health status: For example, pregnancy can affect test results. And certain medications can affect the accuracy of drug screenings.
This isn’t a full list of all the factors that can affect lab results. Even though many things can play a role, you can take steps to minimize inaccurate results.
Are there ways to make sure your lab results are more accurate?
It can be stressful to get lab results that might not be accurate. To set yourself up for the most accurate test results, consider these steps:
Follow any directions your healthcare team gives you to prepare for the test. For example, ask a healthcare professional if you can eat or drink before the test.
If you’re giving a blood sample, stay hydrated. Drinking water keeps more fluid in your veins, which can make drawing your blood easier.
If you’re giving a urine or stool sample, check with a healthcare professional if you have provided a large enough sample. Sometimes too little urine or stool can make it harder for the test to provide an accurate result.
Do your best to stay calm and relaxed when the lab sample is being collected. This improves the chances that you or the technician will get a good sample.
And don’t be afraid to trust your gut. If your test comes back with a result that doesn’t seem right, talk with your healthcare team about it. They may be able to repeat it or run other tests that can help figure out what may be going on.
What to look for in a lab result
As we mentioned, tests usually prioritize either sensitivity (the ability to detect positive cases) or specificity (the ability to detect negative cases) — but not both.
If you want to know with certainty that you have a disease, look for a test with higher sensitivity (fewer false positives). For example, if your chances of survival improve the sooner you identify and treat a disease you may have, then sensitivity is more important than specificity.
And if you want to know with certainty that you don’t have a disease, look for a test with higher specificity (fewer false negatives). Consider the flu in this case. If you want to be sure you don’t have the flu before going back to work, specificity is more important.
You’ll also want to make sure the test itself is credible. If you’ve ordered an at-home test kit, make sure the FDA has authorized it and that it comes from a reputable manufacturer. If you go into a testing center, you’ll want to check that they are a trusted organization.
Frequently asked questions
Lymphoma might show up on a blood test — but not always. It can sometimes lead to abnormal counts of certain blood cells. But the only way to diagnose lymphoma is with a tissue biopsy of an affected lymph node.
Yes, vaping can affect the results of certain blood tests, such as:
It depends. There are newer blood tests that can measure certain proteins in the blood that are more likely to be elevated in people with Alzheimer’s disease. But a positive result doesn’t always mean someone has it, and a negative result doesn’t always mean someone doesn’t have it. An Alzheimer’s diagnosis requires more than just a blood test — it takes into account other tests as well as someone’s symptoms.
Lymphoma might show up on a blood test — but not always. It can sometimes lead to abnormal counts of certain blood cells. But the only way to diagnose lymphoma is with a tissue biopsy of an affected lymph node.
Yes, vaping can affect the results of certain blood tests, such as:
It depends. There are newer blood tests that can measure certain proteins in the blood that are more likely to be elevated in people with Alzheimer’s disease. But a positive result doesn’t always mean someone has it, and a negative result doesn’t always mean someone doesn’t have it. An Alzheimer’s diagnosis requires more than just a blood test — it takes into account other tests as well as someone’s symptoms.
The bottom line
Getting back lab results can be stressful, especially if they don’t seem right. And it’s nearly impossible for a test to be right 100% of the time. Some tests are better at detecting disease, whereas others are better at detecting the absence of a disease.
While no test is perfect, you can take steps to maximize the accuracy of your lab results. And if you aren’t sure about the results, your healthcare team can repeat the lab or run other tests to help you figure out what may be going on.
Why trust our experts?
References
American Diabetes Association. (n.d.). Statistics about diabetes.
Centers for Disease Control and Prevention. (2026). Hypertension.
Centers for Disease Control and Prevention. (2026). Rapid influenza diagnostic tests.
Dahal, S., et al. (2025). Changes in cardiovascular disease risk, lung function and other clinical health outcomes when people who smoke use e-cigarettes to reduce cigarette smoking: an exploratory analysis from a randomised placebo-controlled trial. BMJ Open.
Hammond, D., et al. (2025). Nicotine exposure from smoking tobacco and vaping among adolescents. JAMA Network Open.
Rose, J. J., et al. (2023). Cardiopulmonary impact of electronic cigarettes and vaping products: A scientific statement from the American Heart Association. Circulation.
Wang, Y., et al. (2022). Association between electronic cigarettes use and whole blood cell among adults in the USA-a cross-sectional study of National Health and Nutrition Examination Survey analysis. Environmental Science and Pollution Research.
