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3 Key Differences Between Medical Screening and Diagnostic Testing

April 18, 2023


“Wellness testing can improve health and improve lives by finding health problems even before symptoms occur.”
- Dr. Deborah Sesok-Pizzini, chief medical officer of Labcorp Diagnostics


Since the beginning of the COVID-19 pandemic, the world has become increasingly aware of the importance of testing in healthcare. However, it is important to know the difference between diagnostic testing and screening. Both can help save lives, but screening and diagnostic tests have different use cases and may need to be used together to create an overall picture of your health.


What are the key differences between screening and diagnostic tests?


1) It’s all about the signs and symptoms

We all know the key signs that we’re ill. We call them “symptoms” or “signs,” and they’re our body’s way of telling us something is wrong. Screenings and diagnostic tests initially differ based on their intended users and whether they’re symptomatic or not.

Screening tests are intended for asymptomatic (showing no or disguised symptoms) people, whereas diagnostic tests are intended for those showing symptoms in need of a diagnosis. Often, they are used together: a screening test is first performed to see if your health is on track, and a diagnostic test is then performed to either confirm or eliminate potential results.


2) Slightly different goals

What makes screening tests so valuable is their ability to detect risk. The goal of screening is to detect diseases or issues earlier, provide surveillance and help reduce the risk of disease. Though screening tests may detect irregularities or potential issues, they may not provide answers. If there is need for further diagnosis, that’s where diagnostic tests are used.


What makes diagnostic tests so valuable is their accuracy and specificity when it comes to results. An easy way to remember the key purpose of a diagnostic test is in the word itself: diagnosis. The end result of a diagnostic test is to diagnose an issue or problem.

3) Simplicity of use

Screening tests tend to be less invasive than diagnostic ones—and they are usually simpler to perform. In some cases, you’re able to get the results right at home as well. This is one of the reasons why more direct testing options have become available in the past few years.


For example, rapid antigen (screening) and even PCR tests with at-home collection (diagnostic) tests have become global conversation pieces during the COVID-19 pandemic. Given that all the patient needs are a nasal swab for collection, testing fluid and a testing strip, these kinds of tests can be purchased over the counter and conducted at home.


Some tests, however, must be performed by a licensed healthcare professional due to the more invasive or more complicated nature of the test.


Furthermore, it is vital to understand that a positive result in a screening test usually requires a more accurate diagnostic test to confirm diagnosis.


To put it another way, screening tests get us in the ballpark, and diagnostic tests let us know the score (even if it’s 0-0). Both are crucial tools in determining one’s overall health. Here are some examples of screening tests and how a diagnostic test is used as a follow up.



So what gets tested specifically? What are some conditions that need screening and diagnostic testing?


Screening and diagnostic testing for colon cancers 

For example, a fecal immunochemical test (FIT) is a screening test designed to catch any bleeding in your digestive tract, a key marker of potential colon cancer. It requires no preparation or thick liquid drinks, as are required for a colonoscopy or sigmoidoscopy. Typically, you will be supplied with a kit to use at home. All you have to do is follow instructions provided with the kit, provide a stool sample and then either mail or return it to your physician, healthcare practitioner or lab. A FIT test will indicate whether or not further testing, like a colonoscopy—a more invasive diagnostic test—is needed.


Screening and diagnostic testing for genetic conditions (pregnancy)

For expectant mothers, the safety and health of their baby is a primary concern. Noninvasive prenatal tests (NIPTs) screen women’s blood to look at the genetic health of her developing baby. These tests can be performed in any of the three trimesters and are intended to provide an initial genetic assessment.


These kinds of screenings are very helpful in telling you the chances of your baby having a chromosomal abnormality such as trisomy 21 (Down syndrome). If your screening is positive, that doesn’t mean that your baby has a chromosomal abnormality. For confirmation, your doctor may perform other diagnostic tests, such as amniocentesis or chorionic villus sampling (CVS). These will tell you with greater than 99% accuracy whether your baby is affected with Down syndrome or trisomy 18.


Screening and diagnostic testing for blood analysis

complete blood count (CBC) can be used as a screening test to analyze the cells that circulate in your blood. It’s the most common test ordered by physicians because it provides valuable information regarding your overall health and is the first step in detecting problems like anemia, inflammation and infection. Some diseases are great at hiding. In fact, people may have anemia and not even know it, especially frequent blood donors, people with restricted diets or women of childbearing ages. Anemia can be significantly dangerous if left untreated or uncaught, but a CBC may help identify those at risk. If your physician notices something in your CBC test results, they may send you for further testing to diagnose a specific disease, like an anemia or diabetes test.


Screening and diagnostic testing for diabetes

Testing for diabetes can be nerve wracking and time consuming. You may be seeking clearer insight about your blood sugar levels and want to learn more without having a doctor’s appointment. We offer Diabetes Risk (HbA1c) diagnostic tests to monitor blood sugar. Other tests, such as our Comprehensive Wellness test, can also give you a picture of your overall health and risk for diabetes by measuring your sugars, minerals, electrolytes, enzymes and waste products. This will tell you how well your metabolism, liver and kidneys are functioning.


Knowledge is power when it comes to your health

At the end of the day, your overall health is in your hands. Looking and feeling good may not be enough for peace of mind, knowing that some complications don’t necessarily like the spotlight. Taking proactive steps like exercising regularly, eating better and drinking more water are always important, but so is knowing what’s going on with your health. If you haven’t visited your doctor in the last year for an annual checkup, it’s time to make an appointment.


And we can help with the pursuit of that knowledge and answer to the question, “Am I really good overall?”


For our part, screenings get the conversation going and, combined with confirmatory diagnostic tests, they can help you understand what is going on with your health. It is worth noting that screening recommendations differ by age and gender, so download our checklist that outlines the types of screenings you need.


If you use one of our many screening options, make sure you share your results with your doctor or primary healthcare provider so they can best determine the right path forward for you and your overall health.