What’s a “Rule Out”?

Hello! Your website is so interesting!  I just had lab tests done and am trying to read the results with the help you have listed in your website (Lab Result Meaning.)  What exactly do you mean when you say “Rule out“?  Does that mean to test further? Thanks!

Dear Hello: A Rule Out means there are more than one disease that has the same symptom. When we eliminate some of these probabilities, we achieve more clarity until we finally get to the ONE or TWO diseases we think and abnormality may be caused from. Then, we can run more tests (if  necessary) to see if we are right with our assumptions and to see if one thing we think it is has a stronger possibility of being right.

This seems to be a tough thing to explain. Let me try a second way and you tell me which one you understand better.  Then I’ll supply you with an example as well. . .

Doctors put things into a priority system taking into account the history, signalment (age, sex, nationality) and other clues which the patient has been exposed to. From this information, we make a list of probable causes (diseases) and improbable causes (diseases). It’s quite the balancing act. When the scales tip one way the probability that the symptoms are adding up to one specific disease are more reasonable. Then we decide what further tests are necessary to hopefully confirm the most probable disease. Does that make sense?

What is a Rule out?

What is a Rule out?

And an example: Say you go to a doctor because your ankle hurts. You took a pretty bad fall and twisted it.  We’d make some basic assumptions from the clue of trauma and twisting motion to rule in sprain, strain, fracture (compound, compressed, or spiral), and periosteal bruising. These would be high on the rule out list.

But let’s say we asked some more questions and found out that you were 80 years old, arthritic, haven’t taken care of yourself and cancer runs in your family. The first things we thought it was would be a little farther down the list of probabilities (because this patient is older and already has arthritis and possibly cancer or osteoporosis). Now we’d have to rule out more things like arthritis, fractures and bone cancer. Cancer and arthritis are somewhat lower on the list if the patient is in his teens, right?

So, we’d take an X-ray to see if there is a fracture or sunburst bone growth pattern (indicating bone cancer), bone spurs, lipping of the edges of the bone (spondylosis), and we’d check for bone density to rule out a fracture secondary to osteoporosis. We could even see if the ligaments are calcifying at the ends right next to the bone which would cause pain. We’d also turn in some blood to see if there were any cancer enzymes or indications of general malaise. Since rheumatoid arthritis normally happens in younger bodies, we may not run that test because this patient is too old for that to be a high probability (in all probability and statistically we can rule that disease out).

We (or sometimes the person’s HMO) have to make choices on how much money is to be spent on running tests, which ones would be appropriate (and sometimes we’re fooled) and which ones would not. What is the best use of diagnostic dollars to give us the answers we are seeking?

With these extra tests we could tell you most likely what you have and how to treat it because we have ruled out a host of things that is wasn’t.  If a fracture or bone tumor is obvious with an X-ray, then we’ve ruled in that diagnosis and ruled out a bunch of other things it could have been.

Does that make better sense now?

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