Missed and Erroneous Diagnoses Common in Primary Care Visits
bjain at PARTNERS.ORG
Thu Dec 19 21:44:43 UTC 2013
What is required to minimise diagnostic errors, I believe, Is a deeper understanding of the mechanics of clinical diagnosis. There are two important factors which make diagnosis problematic:
(a) The need to diagnose a disease correctly in a given, individual patient and
(b) The almost infinite range of clinical presentations of a certain disease in different patients, varying from highly typical(high prior probability) to highly atypical(low prior probability).
It is important to appreciate that a prior probability is a statistical concept which symbolises distribution of a disease in a series of patients. It is not therefore a measure of prior evidence for a disease in a given individual patient.
What we require in clinical diagnosis, I suggest, is a parameter which allows us to assess a presentation as evidence for or against a disease in a given patient. This parameter, I believe, is a likelihood ratio, which is a comparison between frequencies of a presentation in patients with and without a suspected disease respectively. It turns out the likelihood ratio of any presentation, even if it is high probability is negligible (Sanson et al Thromb., Haemost. 83: 2000, 199-203. for presentations of pulmonary embolism).
Thsi means any clinical presentation, regardless of whether it is high or low prior probability, does not provide any significant prior evidence for or against a suspected disease. It can only be employed therefore to suspect a disease which is then evaluated by a test. If a test result with likelihood ratio of 10 or higher is observed, the disease is then to be diagnosed definitively ( Jasc hke et al in Users guide to medical literature AMA Press, Chicago 2002, 121-140).
The mistake often made , which leads to diagnostic errors, is to consider a highly atypical presentation(low prior probability) as strong evidence against a suspected disease and rule it out without testing.
Bimal P Jain MD, Pulmonary-Critical Care, Northshore Medical Center (Union), Lynn, MA 01904
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