Disclaimer: This is for the purpose of education only. Don’t try to self supplement or self medicate.

What Are CT Scans?

So I’ll start out with the risks of “CT”. Radiation. But it turns out it’s such little radiation, that major societies like the one that protects babies in pregnant women support the use of “CT” when it is indicated. Apparently, it takes several CTs to produce enough radiation to harm a growing fetus. So trust your doctors. Get the CT.

So, what is CT imaging really good at. The old pneumonic “ABC“ is the best general guide, at least. With of course exceptions all over the place. But here you go…

  • “ABC” lights up bright on CT
  • Acute bleeding (if 2° low Fe, won’t show!)
  • Bone
  • Contrast, calcifications

If there is acute bleeding, hemorrhage, things like that, your emergency physician will be interested in seeing where it’s going, and where it’s coming from. So: Acute bleeding. But, Important pearl here is if there’s an iron deficiency anemia, the CT may not pick up the blood flow problem!

That is, if you are trying to see blood flow problems, blood flow may not show up on a CT of a person who is anemic because “CT” relies on the iron in the blood to image it. So. CT for bleeding is unreliable if HCT < 30. If your hematocrit, the percentage of red blood cells in your blood, is low, the CT won’t work in terms of imaging blood flow. That or hemoglobin, those are your best indicators of iron deficiency anemia.

I’ll next turn to the big question of CT versus MRI. “CT” in general is for hard body tissues. MRI is usually the better imaging modality for soft body tissues. But don’t forget ultrasound! Super safe, and very good for most soft tissues.

I’ll next turn to the forever long debate on whether you need to CT somebody before you LP them because of the risk of missing things you should know about before you do an LP that the LP could harm. LP, lumbar puncture, is necessary to identify many problems going on in the spine, and the encasings of the spine, the brain, and the encasings of the brain.

Trouble is, if you LP somebody that is having mass or mass effect problems in their central nervous system, you can drop the intracranial pressure enough to herniate the brain. Hardly ever super likely, in reality. But it is an ongoing fear.

These are the general guidelines in the pneumonic “COIN” to guide you in terms of getting an LP before you do a CT in certain patients. So, instead of a pearl for swine, you have a coin for swine. We were treated like swine in med school, hence pearls for swine… Here, you get COIN!


  • CT before LP (so don’t herniate) <-“COIN”
  • Old
  • Immunocompromised
  • Neurological finding(s)

If the patient is elderly, they are much more likely to herniate their brain. If the patient is immunocompromised (AIDS, cancer), they are much more likely to herniate their brain. If a patient has neurologic findings on exam like cranial nerve deficits, usually identified by gross inabilities to speak or walk or shake your hand when you walk in the exam room… Those patients… I would definitely get a CT on before I did an LP on them.

So, it’s important to “CT” these people above to see what’s going on inside their brain and spinal cord before you lumbar puncture them to relieve pressure or identify a diagnosis by sending cerebrospinal fluid to the lab.


CT imaging folks. Multiply the complicated thinking I’ve explained above times about 1 million, and you are ready to decide who to “CT”, who to avoid.