Now that the waves have abated a bit after I threw the half-brick of
my friend John's contributions into the pond of discussion on GM/GE
foods, perhaps I could contribute another issue on which I'd welcome
feedback. It does follow on to some extent from recent postings
about healthy living outlets, but it also relates to my own
professional involvement in "near patient testing" (US terminology
is "point of care testing").
POCT in hospitals & GP surgeries has existed for a long time,
ranging from simple qualitative dipstick tests to analysers in
critical care areas such as ICUs. These are not without problems -
patient deaths resulting from use of poorly maintained equipment by
untrained medical & nursing staff resulted in the issue of 2 Hazard
Notices by the Dept of Health a few years ago, recommending that
such equipment should be supervised by Pathology staff, who should
train users in its use and ensure that proper Quality Control and
Assurance systems are in place. This makes the operation of POCT
safe, but expensive. The Medical Devices Agency also issue reports
on equipment and have recently been interested in the wider aspects
of how POCT is used.
Advances in analytical technology are introducing new diagnostic
possibilities in the lab, but are also simplifying equipment for some
tests so that they can be done outside the lab, by people who are not
scientifically trained - eg health food shop staff and people
offering tests as a business. (Some pharmacists offer tests - they
are, of course, health professionals). If equipment is properly
maintained, with QA in place and proper advice/counselling available
to purchasers, then there's little danger, although from a quality
point of view, better advice is likely to be available from GPs, who
would know the person's full clinical picture and could order any
necessary diagnostic tests from the local lab (free of course).
There have been recent prosecutions over improper use of such
extra-laboratory testing, but there are wider concerns. Many
people - not just non-scientists - are surprised to learn that
individual tests rarely give 100% definite answers (an exception
might be a pregnancy test, which of course would be interpreted in
the context of other evidence). There are false positives and false
negatives inherent in the whole testing process, and in clinical
biochemistry at least, diagnosis is generally made from the results
of several tests which are interpreted within a clinical picture plus
consideration of prevalence (application of Bayes Theorem). An
example is blood cholesterol levels and cardiac risk - fine
(assuming that the result is analytically OK) if interpreted along
with smoking, blood pressure, family history, obesity and exercise,
but in commercial situations it often isn't and people can be
inappropriately reassured.
Biochemical screening for osteoporosis is a recent one causing
concern - there is no effective single biochemical test for this (as
far as I'm aware a bone density scan is the best test anyway) and
there are reports of worried patients going to their GPs after
getting some commercial test results which suggest that they have a
problem (why didn't they go there in the first place?).
There are lots of other examples - but what do you think;- would you
buy a commercially offered screening test? If so, why? If not, why
not? Is this sort of test availability - which is likely increase -
a good or bad thing?
Dr MJ Pearson
Department of Chemical Pathology & Immunology
Old Medical School
Leeds General Infirmary (Leeds Teaching Hospitals NHS Trust)
LEEDS LS1 3EX
Tel 0113 392 3945
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