Perforated appendix not seen on CT scan

From an email received two days ago. Posted with permission and edited for length and clarity.

I came across your blog while looking for information on something puzzling that happened to my sister. I read the blog on CT scans and appendicitis* and went through all of the comments section. I couldn't find a case like my sister’s.

She has been sick off and on for the last two months. It began with what seemed like a bad stomach virus, fever, throwing up, diarrhea, gas pain, bloating, and stomach cramps. She brushed it off as a 24 hour type thing, stayed home from work a few days, and felt better but never returned to normal. She would have intermittent stomach upset and began to have weight loss. About 3 weeks ago, she went to see her GP who ran some tests (antibody tests, no CBC, chem 7 or normal work up) and diagnosed her with gluten intolerance.

1 in 20 Americans are misdiagnosed every year

Really?

A paper published in April found that about 12 million Americans, or 5% of adults in this country, are being misdiagnosed every year. This news exploded all over Twitter. Anxious reports from media outlets such as NBC News, CBS News, the Boston Globe, and others fanned the flames.

The paper involves a fair amount of extrapolation and estimation reminiscent of the "440,000 deaths per year caused by medical error" study from last year.

Data from the authors' prior published works involving 81,000 patients and 212,000 doctor visits yielded about 1600 records for analysis.

A misdiagnosis was determined by either an unplanned hospitalization (trigger 1) or a primary care physician revisit within 14 days of an index visit (trigger 2).

A quote from the paper [Emphasis added] : For trigger 1, 141 errors were found in 674 visits reviewed, yielding an error rate of 20.9%. Extrapolating to all 1086 trigger 1 visits yielded an estimate of 227.2 errors. For trigger 2, 36 errors were found in 669 visits reviewed, yielding an error rate of 5.4%. Extrapolating to all 14,777 trigger 2 visits yielded an estimate of 795.2 errors. Finally, for the control visits, 13 errors were found in 614 visits reviewed, yielding an error rate of 2.1%. Extrapolating to all 193,810 control visits yielded an estimate of 4,103.5 errors. Thus, we estimated that 5126 errors would have occurred across the three groups. We then divided this figure by the number of unique primary care patients in the initial cohort (81,483) and arrived at an estimated error rate of 6.29%. Because approximately 80.5% of US adults seek outpatient care annually, the same rate when applied to all US adults gives an estimate of 5.06%.