Accuracy of Diagnostic Laboratory Medical Tests: Specificity and Sensitivity

[Guest guest]

Accuracy of Diagnostic Laboratory Medical Tests:

Specificity and Sensitivity

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An acquaintance recently mentioned that " 20/20 or one of those news shows

just did a piece on the use of hair testing. They sent a standard poodle's

hair in for testing to 4 or 5 labs and got different results from each. I

have come to the educated conclusion that hair testing is a great farce. But

for some it might lead to being treated by just the thing that their body

needs. But don't think it would be due to the accuracy of testing, just

luck! "

The following is information to help anyone, including medical

professionals, understand why diagnostic tests have widely varying accuracy.

The

reasons for the levels of accuracy depend on a variety of factors.

Results from most diagnostic tests, not just hair testing, will differ

from laboratory to laboratory. There are several reasons for this, ranging

from the training and skill of the lab technicians to proper test set-up

protocol (for example, when analyzing hair samples, which portion of the hair

shaft the sample came from is critical), to - as 20/20/whoever was trying to

point out - the actual ability of the test to measure what it is supposed

to measure.

We know of labs in Wisconsin that were given awards when their accuracy

rate (that is, their rate of correctly carrying out tests from start to

finish) was 97%, and I would guess that nationwide that is considered an

'award-winning' rate of accuracy for correctly doing diagnostic tests.

But this whole issue raises a point that is key to understanding the

accuracy of any diagnostic test: even with the best of training and perfect

protocols, laboratory tests do not yield yes/no answers. The accuracy of the

tests are derived from statistical distributions. Because of this, the rarer

a condition in the general population, the higher the probability that a

laboratory test will yield inaccurate results.

Here's a bit of explanation to help understand why I say that.

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