Uncertain values amidst randomness?

A paper on the early detection of cancer describes some problems of the screening process using Prostate-Specific Antigen (PSA) testing.  The marker is not specific for cancer, has an uncertain cut-off value, varies naturally, and leads to unnecessary interventions which are often harmful. Reviewing large and contradictory clinical trials, the authors say,

“But it was impossible to address so many probabilities and uncertainties coherently during routine office visits. Thus, patients were not really making informed decisions, and office-based discussion of the pros and cons of PSA testing was essentially a charade. Instead, most patients’ decisions reflected their general concerns about cancer or their general inclination to accept (or resist) medical interventions….

“These approaches to managing serial PSA levels reflect either a fundamental misunderstanding of — or an unwillingness to acknowledge — PSA’s limitations as a marker for early prostate cancer. Observational studies show clearly that PSA levels fluctuate spontaneously, moving above or below whatever threshold clinicians deem worrisome. In addition, random biopsies can detect prostate cancer in 12% of men with PSA levels below 2 ng per milliliter and in 25% of men with levels between 2.1 and 4.0 ng per milliliter4; the latter figure approximates the prevalence often reported for men with levels between 4.0 and 10.0 ng per milliliter. When the PSA goes up — for example, from 3.0 to 4.0 ng per milliliter — and triggers a biopsy that reveals cancer, clinicians refer to “PSA-detected cancer.” But many of these cancers are not really detected by PSA screening; they are incidental findings against a background of randomly fluctuating PSA levels and an age-related increase in prostate-cancer incidence…

“For two decades, primary care physicians have been expected to present a flawed screening test to patients, cloaking the flaws in an elaborate ritual of informed decision making. In turn, men have been expected to make sense of a confusing mix of hypothetical outcomes.

Considering the work of clinical chemistry in determining PSA levels obliges us to ask, How could record-collection and metrical perfectionism applied to lab results improve diagnosis when many uncertainties are much larger?

Would “confidence” in a more accurate or precise PSA value make a diagnostic difference?

How long before the dramatics of accreditationism are widely seen as a charade that does no clinical good?  

Is inspectionism just clutching at the straws of uncertain values in a sea of randomness? How much longer will it keep the darkness at bay?

Or was science founded on confidence in experimental predictability long before accreditationism arose?  Michael Faraday said,

“All our theories are fixed upon uncertain data, and all of them want alteration and support from facts.”  “One thing, however, is fortunate, which is, that whatever our opinions, they do not alter nor derange the laws of nature.

This entry was posted in Laboratory medicine, Medicine, NHS, Practical problems, Questions and tagged , , . Bookmark the permalink.

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