Posts Tagged ‘Wasserman test’

Blizzards, syphilis, and nosology (the study of how we know what we know)

December 12, 2010

How do we know what we know?

If the test says ‘yes’, is it so?

     False positive rates

     In some disease states

Can lead to some terrible woe.

 

Cold came to Iowa overnight, strong enough to generate national news.

I arrived to make hospital rounds yesterday, and talked with the doc on call.  We eyed the weather reports and I took over call early, allowing the other physician to get home before a blizzard hit.

Patients like to stay sheltered when the wind chill goes to double negative digits, only the much sicker come in. The forecast called for 40-50 mile per hour winds, heavy snow, and temps around zero.  After supper I packed an overnight bag and returned the half-mile to the hospital.      

I didn’t have to stay the night at the hospital; I could have waited to get called.  I wasn’t sure the blizzard would really happen, but I didn’t want to face whiteout conditions trying to get to the ER. 

I drifted to the nurses’ station first.  With a census of three, the staff outnumbered the patients.  We chatted about the cold, deer season, and the patients.  I got some surprise lab results.

Mostly we get information from laboratory tests to confirm what we think is wrong; rarely (not never) do we generate as much decision making from x-rays or blood and urine tests as we do from talking to the patient.  Sometimes the patient can’t talk, can’t remember, or won’t tell the truth.  In those cases lab and x-ray add heavily to the diagnosis.

Yes, I ask for tests “just to make sure,” and sometimes when the case perplexes me I’ll order a large number of lab tests.  Ninety percent of those results come back as expected.  Ten percent of the time they don’t.

I finished residency thirty-two years ago, when syphilis used to be called the ‘Great Pretender’ because it could mimic any other disease.  As med students we learned to order certain labs as a matter of course, especially the serologic test for syphilis, aka STS, Wasserman test, VDRL, or RPR.  Later we learned to order the confirmatory test, the free treponemal antigen (FTA) or Treponema palladium plasma antigen (TPPA). 

As rates of syphilis fell, the disease changed and enthusiasm for testing waned.  In medical school, we were taught that the infection always started with a sore.  By 1990 the sore happened occasionally.  Now we almost never find one.

I still test for syphilis despite low rates.  Since 1982 on five occasions the test came back positive and surprised us all; on one occasion, years ago in another place, the positive result startled me but not the patient.  I came away with a history lesson in riverboats and an appreciation for Midwestern life in the thirties. 

The diagnosis remains a problem in nosology.  The first test has false positives (as in Lyme disease) and false negatives (late in the illness), the second test has no false positives but cannot distinguish active disease from prior infection.  In the end, there is no substitute for clinical judgement.

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