have you had test

Have you had the test?

When we hear about celebrities being ill or admitted to hospital we

hear phrases like `undergoing tests' and `tests showed that...'.

`Tests' are obviously very important and a lot hangs on the results.

`Tests' are safe and always right. Aren't they?

We've all seen patients where the test gets it wrong; the normal x-ray

in the patient with bone metastases or the dangerously high potassium

level due to a dodgy blood sample in a normal patient. In these

circumstances we know the limitations and problems with the test and

can repeat the test, do a different test, or even ignore the result.

I'm sure that all medical students and junior doctors have had some

rules about diagnostic tests drummed into them by their seniors:

If you don't know why you're doing a test you shouldn't be doing it

If you don't know what you're going to do about the test result when

you get it you shouldn't be doing it

If the result of the test isn't going to change or aid in the

patient's management you shouldn't be doing it

Treat the patient not the result (all tests can produce false positive

or false negative results)

This avoids patients having unnecessary tests and unnecessary or wrong

treatment based on incorrect results. Obviously unnecessary treatment

could be risky with surgical complications or drug side effects but

some tests carry their own risks, for example radiation exposure

(x-rays, CT scans etc), bleeding (liver biopsy) or other injury

(colonoscopy, diagnostic procedures under anaesthetic).

We try to take these problems with diagnostic tests into account but

sometimes doctors as well as patients can become over reliant on them

for diagnosis or reassurance (or medico-legal reasons). Many of the

diagnostic tests we do have had their reliability studied in depth

before they are recommended for everyday use because it's important to

understand how often and in what circumstances a test is likely to

give a false result. Newer tests are still being studied and developed

and we're often cautious about them. The histopathologists out there

will know about the latest immunohistochemical stains which show early

promise at differentiating benign from malignant or being highly

specific for a certain type of tumour. When more research is done they

are often not quite as good as we initially thought, although they may

still be useful.

In 2003 the RCPath produced some draft guidelines: Who can request a

test? This document then seemed to vanish but over three years later

it is finally being revised into a more definitive form. The draft

version states:

`the test must not only be ordered appropriately, but also... the

result must go back to someone who can take appropriate action.'

(sounds just like what your consultant told you when you were a house

officer).

On a related note they've also released this report: Evaluating and

introducing new diagnostic tests: the need for a national strategy.

This document talks about some of the things I've mentioned above

about the reliability of tests and summarises the issues that must be

looked at when introducing new tests, the first of which is:

`Is the scientific evidence for the validity of the new test

sufficiently robust?'

The report also goes on to state:

`There is increasing pressure to introduce new tests precipitously,

without rigorous evaluation of their true utility, when related to

emotive topics (such as cancer) or when there are possible medicolegal

threats.'

`It is difficult for staff to evaluate recently introduced tests

objectively and consistently across the NHS; published evidence

demonstrates that papers on the diagnostic accuracy of new tests are

often of poor quality and to make a good decision is difficult.'

The RCPath might be a bit late with these documents as increasing

numbers of `diagnostic' or `screening' tests are being offered to

anybody with the money to pay, as well as the time and stress

resilience to cope with subsequent investigation of their

incidentalomas.

Shinga has written about some of the allergy tests available and

finds, via some dedicated literature searching, that they aren't as

reliable as some suggest. Despite the amount of work that should go

into studying tests, Shinga has found that tests can be let loose on

the public without being properly validated, and worrying they can be