Why medical tests are worthless

Why medical tests are worthless


I am frequently asked by patients to “run some tests to make sure nothing is wrong.” This makes a lot of sense on the surface, but makes no sense as a physician. Why? Because testing without a context or a medical question is nonsensical. Let’s talk about why.

How doctors think

It’s frequently quoted that doctors only let their patient speak for 11 seconds on average before we interrupt them. This suggests that doctors don’t listen to patients when actually we are listening for specific things to help us figure out how to help you.

From the moment I meet you, I’m thinking about problem solving your health issue. Chest pain? I’ve already created a list of dozens of possible problems from heart attack to muscle strain in my mind. I need specific information from you and from my examination of you to narrow that list down. Sometimes doctors jump the gun in trying to get the specific questions we need answered to rapidly narrow down the list of potential diagnoses. You may not know what the most important medical information is, so we try to direct your sharing of information to get to these issues most quickly. I’ve personally found over the years that the best way to get the most complete information is to say: “Tell me about when you started feeling sick and how your illness has progressed since then.” The majority of people give me a great timeline of their illness. Some have difficulty and this is when more directed questions need to be used.

It may also seem like my examination of you is cursory. This is, again, because I’m looking for very specific things to further narrow down your problem. It’s not likely that listening to your heart is going to give me useful information about your ankle injury, for example. Sometimes the exam isn’t helpful at all. For example, if you have the right symptoms of a simple urinary tract infection, an exam is not likely to add anything and moving on to urine testing makes sense.

Hopefully, after getting the story and examining you, I’ve gotten your list of possible problems narrowed down to less than five possibilities. Here is where actual testing comes into play. We use lab tests, imaging studies and procedures to get that list of problems narrowed down to the one problem you actually have. This is key. No clear diagnosis means no clear treatment plan. For example, you may have a swollen, painful knee. If it’s not clear why after I talk to and examine you, it’s time to do some testing. This may include an x-ray to look for a bone infection or blood work and sampling of the fluid in your knee to look for an infection or gout.

Sometimes it is not possible to make the diagnosis confidently, especially within the confines of limited resources and time in the emergency department (ED). At this point we can suggest measures to reduce symptoms and direction as to what to do next to get the diagnosis nailed down.

Shouldn’t test results give us the answer regardless?

Test results don’t mean anything out of a clinical context. Every test can give us false results. Some tests make us think you have one problem, but having spoken to and examining you shows that you actually have a different problem that looks similar. For example, I can get a chest x-ray of you and the radiologist can look at it and tell me that you have pneumonia. But that doesn’t mean you have pneumonia. Blood clots to the lung (aka pulmonary embolus) can look like pneumonia on a chest x-ray. Treatment for pneumonia and pulmonary embolus are different. The story of your illness is usually different for these problems.

Some tests will not identify the problem but simply rule out problems that can be mistaken for your problem. For example, parents may bring their toddler into the ED with a complaint of elbow pain. She may be crying. The parents may be concerned about a broken bone because she was walking hand-in-hand with her mom when she tripped and mom grabbed her by the arm to keep her from falling. Now she is crying because of elbow pain. But, I know that a broken bone is not likely in this circumstance. Given the right exam, the proper next step is not a test, but a treatment, specifically a maneuver to fix a nursemaid’s elbow.

Some tests will be straight-up misleading. Is a positive strep test diagnostic of strep throat? Not always. The strep test should be performed when someone has signs of strep throat. The test is a piece of the puzzle. It’s estimated that 25-37% of people have Group A strep (the cause of strep throat) in their throat all of the time (aka carriers). If I swab the throat of a Group A strep carrier, the test will be positive even when they are not sick, meaning that treating them with antibiotics is unnecessary. We know that if you have a runny nose, cough and a sore throat, it’s probably a cold and a test is not helpful because it’s more likely to give us the wrong diagnosis (ie. it will tell us you have strep because you’re a carrier, not because you actually have strep throat). If you have a headache, fever, sore throat and no other signs of a cold, it’s 50-50 if you have strep throat. This is when a test helps because if the test is positive, it makes sense in the context of your illness and is not likely to simply reflect a carrier state. A more advanced discussion about this can be found in this podcast.

There is no benefit to getting tests for the sake of “making sure there’s nothing wrong”

As I’ve discussed above, doing testing when we’re not trying to further evaluate a clinical question is not helpful. Tests are interpreted in the context of a clinical problem.

We’ve seen the increase in number of direct-to-consumer tests. Handing over cash for a body scan, genetic testing or food allergy testing is fraught with pitfalls and land mines.

Full body CAT scans (computed tomography) not only expose you to a lot of radiation, but frequently identify things that are not dangerous (aka incidental) but lead to further testing either with more scans and radiation or procedures to biopsy things that did not need a biopsy. We may not even know how to interpret a scan finding in the absence of symptoms because there have been no scientific studies that give us information about the implications of your findings in the absence of symptoms of illness.

Getting genetic testing is alluring. Who wouldn’t want to unlock their body’s secrets by getting a full report on their genes? Unfortunately, we know that our genes don’t tell the whole story. Twins who are genetically identical aren’t always identical in their lives or their illnesses. We also don’t fully understand how to interpret genetic studies. In some cases, like with the BRCA1 and BRCA2 genes for breast and ovarian cancer, we know of the benefit, when it should be used, and how it should be interpreted. Even then, testing can give falsely positive or falsely negative results or may identify a mutation to the BRCA1 or BRCA2 gene that has not been adequately studied so we have an indeterminate result. Many people with a BRCA1 or BRCA2 gene mutation associated with cancer will not actually develop cancer. This is when consultation with a geneticist is key. Knowing what to do with your results makes all the difference.

I’ve recently seen ads for at-home allergy testing. Have you ever wondered why there are allergists? Because allergy issues are complicated! If it were as simple as running an at-home test, an allergist would not need 4 years of medical school followed by 3 years of internal medicine or pediatrics training and another 2 years of fellowship training. Allergies are an area rampant with false positive tests, meaning that tests can tell you you’re allergic to something, but when you actually are exposed to the allergen, you don’t get symptoms of an allergy! False negative tests happen a lot too, meaning the test says you’re not allergic but you actually are. Neither of these situations is ideal. An allergist is trained to understand which tests are most likely to give a truthful result in which context. They are trained to differentiate between what is likely to be a false result and what is likely a true result. Check out more about food allergies here.

Medical testing is fraught with confusion, misinformation and pitfalls. It would be great if I could “run some tests to make sure nothing is wrong”, but unfortunately it is not as simple as this. Like going to another country where you don’t speak the language, an interpreter is key to not only understand what other people are saying to you, but to interpret the cultural implications of things that you encounter. Please consult with your doctor about why, when, and how medical testing would most benefit you.

If you live in Massachusetts and have questions about your medical testing, make an appointment for a video chat with me at www.my-doctor-friend.com.