Arriving at a diagnosis is the intellectual end point of defensive medicine.
Defensive medicine is directed at finding the definitive test to establish the
diagnosis or doing enough tests to rule out other possible diagnoses. This ruling
out is considered an important legal protection should someone later
determine the patient’s actual problem.
The ruling out of alternative diagnostic hypotheses is a valid strategy if the
universe of possible alternatives is sufficiently large. But it is a dangerous
strategy if the initial diagnostic assumptions constrain subsequent data
collection and hypothesis generation. The physician must guard against
ignoring the patient’s stated problem in favor of a diagnostically tidier problem.
For example, if the patient has trouble walking because of a plantar wart, the
physician should not attempt to repair the patient’s asymptomatic slipped disk
as a substitute for removing the plantar wart.
This emphasis on diagnosis leads to laboratory diagnosis as the ideal of
technological medicine. [Fortess EE, Kapp MB. Medical uncertainty, diagnostic
testing, and legal liability. Law Med Health Care. 1985;13:213–218.] Clinical
laboratory tests are seen as objective, while taking a history and physical is
subjective. Laboratory tests are easy to replicate, may be discussed without
reference to the context of the specific patient, and, at least superficially, are
easy to interpret. Tests with numerical results lend an air of science to medical
Before the advent of digital electronic calculators, calculations were worked out
with slide rules. When digital calculators became cheap enough for general use
in the classroom, many teachers opposed their use. There was a philosophical
concern with the false rigor that electronic calculators created. The slide rule
was accurate to only two or three digits; thus, using a slide rule constantly
reminded the student of the approximate nature of the underlying data. Digital
calculators and digital reading instruments display many digits—but most
medical data are approximate, usually to only two digits of accuracy and
sometimes less. Manipulations of these data that do not take into account their
limited accuracy lead to spurious results, but results that appear to be scientific
because they are numerical.
This problem of false rigor is exacerbated by the use of multiple test panels.
These panels include large numbers of tests that measure mostly unrelated
parameters. The test results are expressed numerically, but the evaluation of
the results depends on the comparison of these numerical values with normal
values. Normal values are determined by statistical techniques. They are
usually set such that 5% or 10% of healthy people given the test will have
values outside the normal range.
When a patient is given a panel with 20 independent tests, each with a normal
value defined by the 95th percentile, then the probability is high that at least
one test will be falsely normal or abnormal. The noise from the false test
results makes it more difficult to evaluate the diagnostic content of the test
panel and increases the chance that important information will be lost in the
mass of data. The tests may also document important problems that the
physician missed. When an injured patient seeks the advice of an attorney, the
attorney has the luxury of working backward from the injury. If the physician
did not order the proper tests, then all the other tests that were ordered
become irrelevant. And if the proper test was ordered but the results were
overlooked or ignored, the emphasis on ordering tests accentuates the error in
not acting on the relevant test results.