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Why Does Misdiagnosis Occur?

There are many ways that a diagnosis can go wrong. There can be contributing factors from any of the players:

  • Patient
  • Doctor
  • Specialist
  • Tests (laboratory or pathology tests)

Patient: It seems poor form to blame a patient for a wrong diagnosis, and indeed blame is probably the wrong word. Nevertheless, the patient is involved, and can contribute to a wrong diagnosis.

  • Self diagnosis: The most likely way for a patient to contribute to a misdiagnosis is attempting to do so themselves without professional medical advice.
  • Not reporting symptoms: Sometimes patients don't tell the doctors everything. Sometimes symptoms are embarrassing. Other times you might think they're not worth mentioning. Some people won't mention a symptom unless the doctor asks, and assume it must be irrelevant if the doctor doesn't ask about it directly. Always tell the doctor everything, no matter how trivial, no matter if you believe it unrelated. Let the doctor have all the facts.
  • Failure to complete ordered tests: In some cases, patients don't get diagnostic tests done, even when a doctor has ordered the tests. This can occur due to oversight, complacency, laziness, or embarassment. For example, one contributing factor to delayed diagnosis of colon cancer is patients' perceived embarrassment over tests such as colonoscopy and sigmoidoscopy.

Doctor: Since the doctor has to make a diagnosis, it is certainly possible to make the wrong diagnosis. There are many ways that this can occur.

  • Doctors know only common diseases: There are more than 20,000 human diseases, and doctors only know the most common.
  • Over-publicized diseases: Any diseases that get a lot of attention tend to get over-diagnosed somewhat. This means that less common diseases that might have similar symptoms are sometimes overlooked.
  • Different doctor skill levels: Not all doctors are alike. A general practitioner is well versed in common diseases but not in rarer areas that a specialist would know better.
  • Doctor bias: All doctors are human and have biases. They can have the "hammer-and-nail" bias: if you have a hammer, everything looks like a nail. If they see a certain disease frequently, they will diagnose it frequently, and might make an error if it is not that disease, but something with similar symptoms. This tendency to go with what is familiar is also seen in treatments, where a surgeon will recommend surgery more often, but an endocrinologist will recommend pills more often.
  • Saving you money: Some doctors will avoid tests, assuming that you don't want to pay extra costs. For example, if there is a very rare condition, say 1-in-200, should your doctor get you to test for it? Some doctors won't even tell you about this type of test. This works fine for the majority, but fails for the very small percentage who might have the second disease.
  • Choice not to analyze deeply: In some conditions, the doctor may consider it adequate to get the overall disease, and less important to confirm the subtype of the disease.
  • Lack of time: It really is quite sad how little time a doctor will typically spend with a patient. We're all used to something like a 15 minutes appointment. That doesn't give the doctor much time to ask a few questions, make a tentative diagnosis, order some blood tests to confirm it, and then answer some questions from the patient. We'd all like to think that, later, the doctor went and double-checked our disease in their books, with other specialists, and consulted the latest research about how to diagnose and treat it correctly, but it seems rather unlikely! In reality, doctors have to shoot from the hip, and although they'll hit the mark with most common diseases, they can get tricked up by rarer conditions.
  • Behavioral/mental symptoms hard to analyse: Some types of symptoms are just hard to understand. This is particularly true of those regarding emotional or mental well-being.

Laboratory and pathology tests: The various medical tests that are used to confirm or rule out diagnoses can also sometimes fail. They are useful diagnostic tools, but are not perfect.

  • Human errors: Of course, a simple human error can occur in any of the various tests. For example, samples could get contaminated or mixed up, or the test procedure might get done improperly. Some tests require visual inspection, such as cell tests for cancer (e.g. Pap smears), and rely on the human judgement of the person inspecting them. Naturally errors are rare, but can occur.
  • Error margins: false positives, false negatives. All laboratory tests have known conditions under which they fail. They can either fail with a false positive, wrongly indicating that you have a condition when you don't, or a false negative, wrongly indicating you don't when you actually do. Either way will get you the wrong diagnosis. Most tests fail very infrequently, but if you read the documentation about each test, you'll see that there are known limitations for each test. Some tests fail on some people because of special features about a person. Some tests for one disease will fail if you have some other rare diseases.


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