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The quickest way to get diagnosed with something is to go to a doctor.

October 3, 2012

So let’s talk about screening tests for a moment shall we?  The US Preventative Services Task Force is a group that studies aggregates of clinical trials and comes up with recommendations for screening for a number of diseases.  For example, the USPTF recommends mammography every 1-2 years for women 50-69.  The USPTF recommends cervical cancer screening every 3 years.  For colon cancer, it says everyone should be screened but doesn’t say how often.  The American Medical Association, in a statement in June of this year, says breast cancer screening should be offered to women 40 and older, but they don’t say how often.  The American Cancer Association says cervical cancer screening every 3 years and colonoscopys every 10 years after age 50.  The American society of gastroenterologists says colonoscopy every 10 years if the first one is negative, every 3-5 if polyps are found.  The reason for these inconsistencies is that the amount of evidence to show that a test is going to prevent deaths from any specific disease is astronomical.  Hundreds of thousands of people have to be followed for years and all that data collected and aggregated.  That’s why they are RECOMMENDATIONS.

Lets talk specificity and sensitivity.  SENSITIVITY is the ability of the test to correctly identify a disease.  SPECIFICITY is the ability of the test to correctly identify that you don’t have a disease.  So if you go to the airport and go through the scanner, the alarm might go off from your belt buckle or keys, so the ability of the test to correctly identify a gun or explosive is low (low specificity) but the scanner is set that way so as not to miss something that really is harmful (high sensitivity).  The ideal screening test is 100% on both.  This is essentially impossible in medicine.  In Canada, one study showed that the sensitivity of first time mammogram is 69%.  That means that 2/3 of the people who actually have something will have it pickedup by mammography.  The positive predictive value is different.  Thats the percentage of the time a positive is really positive.  The positive predictive value for mammography is somewhere around 7%.  This means that most of the time a positive finding is really nothing (http://www.cancer.gov/cancertopics/pdq/screening/breast/healthprofessional/page6 .  This is because a very low percentage of women (0.5%) will have cancer at the time of screening.  Which leads me to my next point:

Every positive screening test leads to more screening.  Remember that.  Every positive screening test leads to more screening.  So when you go for a screening test, be it mammography or pap smear or colonoscopy or PSA testing or anything else, think about what you are going to do with the information you get.  Personal story:  I got a mammogram as ordered like a good girl, at age 41.  No family history.  Got the pictures, went home.  Got a call.  They need more pictures.  Go get more pictures.  Well, we need to do an ultrasound.  OK, scared sh—less.  Oh, it’s nothing, just a normal lymph node. 2 weeks, 3 hours in the hospital and a heart attack to tell me what I already pretty much knew.  There’s nothing wrong with me.

Now, if my mother, grandmother, sister and aunt had all died of  breast cancer in their 40s you better believe I would have run to that mammography center begging to be poked and prodded.  Screening can be useful.  The USPSTF acknowledges the real mortality benefit to certain screenings at certain times.  But these tests must be used on an individual basis.  If you are 30 years old and your father and grandfather had colon cancer in their 40s run, don’t walk, to the nearest colonoscopy center.  If you have no history and you’re 30 years old, the chances are that nothing will be found and if it is, that it’s really nothing.  That’s why we don’t screen young people with no history.  The false positives are way too high. 

If you are 85 and you have anemia and your doctor wants you to get a colonoscopy to rule out bleeding ulcers or cancers as the reason for the anemia, think twice.  What are you really going to do with the information?  What if they find “something”?  Would you like to sit in hospitals and doctors offices getting follow up screenings and tests when you feel fine? You gonna get stomach or colon surgery, radiation, chemo, etc.?  Or are you like me and would rather drink cabernet and eat chocolate chip cookies?

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