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Harvard Commentaries
Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School

Medical Myths Medical Myths

Common Conditions with Misleading Symptoms

October 10, 2013

By Robert H. Shmerling M.D.

Beth Israel Deaconess Medical Center

Healthy Lifestyle
Medical Myths
Common Conditions with Misleading Symptoms
Common Conditions with Misleading Symptoms
For many common conditions, symptoms are not a reliable way to make a diagnosis.
Harvard Medical School Commentary

During their training, doctors are taught to listen to patients, ask good questions, perform a physical examination, and order the appropriate tests when needed. Good physicians take pride in their ability to put all of this information together to make a diagnosis. The best doctors are always trying to get better at it.

But, sometimes a patient comes into the office with his or her own diagnosis based on symptoms:

  • "I can tell my blood pressure is high."
  • "I've been tired for weeks. I must be anemic."
  • "I know I have a urine infection; it doesn't smell right."

Now the doctor's task is somewhat different. Using the same diagnostic skills, the challenge is not just coming up with the correct diagnosis. It's also to decide whether the patient is right.

I have to admit: This adds a bit of pressure. My patient may be unhappy with me if I don't agree with his or her diagnosis. But, of course, I have to provide my honest medical opinion.

I recognized long ago that the patient is usually right. This shouldn't be surprising. People know their bodies well. When they're been dealing with a condition for many years, they know what to expect. But for many common conditions, symptoms are not a reliable way to make a diagnosis.

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The Patient Is Always Right — Except When He or She Is Wrong

There is a significant error rate for people who believe they can tell when they have one of these conditions:

  • High blood pressure
  • Anemia
  • A urinary tract infection

But the truth is:

  • Unless blood pressure is markedly (and dangerously) elevated, hypertension typically causes no symptoms at all.
  • Most people with mild anemia feel fine and only learn about their condition when they have routine blood tests.
  • Urine odor can be affected by a number of factors other than a common bacterial infection (often called a urinary tract infection or UTI). These include diet, fluid intake, medications, a yeast infection or diabetes.

Many other conditions have unreliable symptoms as well. For example:

    • Diabetes – Frequent urination, excessive thirst, fatigue and unexplained weight loss are common symptoms of diabetes. But people with normal blood sugar can experience these symptoms. And, many people who are newly diagnosed with diabetes have no symptoms at all.
    • Fracture – You can't rely on the degree of bruising, the ability to move or bear weight, or even the severity of pain to know if you have a broken bone. To be sure a bone is not fractured, you need an X-ray. And sometimes even X-rays don't provide a sure answer. You may need additional tests, such as another X-ray, CT scan or MRI.
    • Hypoglycemia (low blood sugar) – Abnormally low blood sugar is rather rare unless you're taking a medication (such as insulin for diabetes) that lowers blood sugar. Feeling shaky, tired, absent-minded or hungry between meals can be symptoms of low blood sugar. But people with these symptoms usually have normal blood sugar.
    • Strep throat – Fever, painful enlarged lymph nodes and white patches (called exudates) near the tonsils are symptoms that suggest strep throat — a Group A Streptococcal infection. But you can have strep throat without one or more of these symptoms. And many people with these findings don't have strep throat. When in doubt, a throat culture (or other test for strep infection) is quite helpful.


    • Thyroid disease – An overactive thyroid can cause weight loss, heat intolerance, tremors and palpitations. Classic symptoms of an underactive thyroid are weight gain, cold intolerance, fatigue and weakness. But many people with thyroid disease have few or none of these symptoms. Or, even more misleading, they have symptoms of an overactive thyroid and turn out to have an underactive thyroid gland! Many thyroid disorders are discovered by routine testing in people with no symptoms at all.

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The Bottom Line

Symptoms do matter. They may raise suspicion of a condition that's easily diagnosed and treated. But that's not always the case. For some conditions, you can't rely on your symptoms to indicate the presence of health or disease.

The next time a patient tells me he knows his blood pressure, I may not believe it's true. But I won't assume it's untrue either. I'll measure the blood pressure, because that's the only reliable way to know what it is. When it comes to conditions like hypertension or anemia, symptoms can be misleading. But the numbers don't lie.

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Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.


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