There are now many different medical diagnostic tests available on the market outside of the conventional medical referral system. The growing market is driven by increasing personal interest in health, clinical need, limitations of the conventional medical system, greater access to health information, and direct customer demand.

Doctors and medical practitioners can sometimes be justified in dismissing test results that originate from ‘mail order laboratory testing services’, as there is currently no way for them to distinguish between those results which have been clearly validated according to good practice and government guidelines, and those that claim results without any real evidence.

How are the public meant to tell the difference between the many different diagnostic tests that are available to them? How can they tell those based on good science and those that have no basis is science? The following are 7 simple things to look out for when buying a diagnostic test.

1)What regulation in place to protect the consumer?

In order for a diagnostic test to be placed on the market in the UK (and indeed Europe) it has to have been given a CE mark from the manufacturer of the test. This shows that the test meets the essential requirements of the European In Vitro Diagnostic Medical Devices Directive implemented into UK legislation by the Medical Devices Regulations 2002, a piece of legislation that came into force on 13 June 2002. It is now mandatory to comply with this legislation, which covers tests intended for examining specimens from humans, e.g. blood, semen, urine or stool and providing information concerning, amongst other things, physiological or pathological conditions such as allergies and food intolerance.

However please note that this legislation does not cover laboratory testing services and at the moment, in the UK at least, any test can be invented and used in a ‘laboratory’ or other setting; in other words, laboratories can currently provide testing services without using CE marked products without any regulation. Note that any laboratories providing a service to the NHS, with results issued by a medical doctor, must be accredited to standards published by Clinical Pathology Accreditation (CPA).

The CE mark in itself does not guarantee performance, but indicates that the product conforms to certain standards that allow products to be placed on the market.

2) Diagnostic Test Validation

In order to show that results from a specific diagnostic test are meaningful, and can be interpreted and acted upon accurately and effectively, it is absolutely essential that tests undergo rigorous evaluation to make sure that they perform well enough to provide accurate and reproducible information. The thorough validation of a test’s performance can be divided into two categories:-

a) Technical (analytical) validation within the laboratory9 to ensure that systemic errors (leading to inaccuracy) and random errors (leading to poor reproducibility) have been minimised.

b) Clinical validation confirming the test’s potential in a clinical setting

3)Has the test been referenced against a ‘Gold Standard’?

The ideal way to evaluate the diagnostic potential of a test is to make a direct comparison against an existing ‘gold standard’ method. For some tests this is easy, for example tests for thyroid function such as the measurement of Thyroid Stimulating Hormone (TSH). The TSH test is referenced against international reference standard 80/558; there is a recognised national external quality assurance scheme (NEQAS) for measurement of TSH in the UK; and there are many existing TSH assays available for comparison.

Not all new tests will have a gold standard that can be referenced and so in these cases there should be documented criteria against which the test has been assessed. These, of course, can be clinical outcome measures if the test defines treatment or modification to lifestyle.

4)What data is available to demonstrate the test is accurate?

Diagnostic tests are seldom 100% accurate, false negatives and false positives will occur. A test is considered valid if: it detects most people with the target disorder (high sensitivity); excludes most people without the disorder (high specificity); and a positive test result usually indicates that the disorder is present (high positive predictive value). It is also important to consider what proportion of the results, when acted upon with specific treatment or lifestyle changes, show a significant improvement in health of the subjects.

Data should also be available to show that the test actually measures what it says it does and that the test has been designed effectively to overcome factors such as non-specific binding, and cross-reactivity with other similar substances, which can result in false positive results

5) Is the test suitably reproducible?

Again the important issue is whether the reproducibility data demonstrated for the test show that the test Cialis Professional is ‘fit for the purpose intended’. If reproducibility of a test is mediocre, and yet the test still discriminates well between those with and those without the target condition, it can be very useful. Under these circumstances, it is likely that the test can be readily applied. Studies of imprecision11 should take into account variation according to factors such as time, temperature, different manufacturing batch of reagents and operators to give a true picture of how the test really performs. Reproducibility will also define the detection limit of the test. Is the test sensitive enough to pick up small amounts of the particular antibody or target substance being measured that may actually be clinically relevant?

6) Have sample and test stability been validated?

For laboratories providing testing services, validation of sample stability is paramount. These data should be available from the test provider and form part of their technical file to support CE marking of specimen collection. These studies must include validation of sample transport, and the effect of varying temperature.

7) Will patients be better off as a result of action taken based on the test result?

The ultimate criterion for the usefulness of a diagnostic test is whether it adds information beyond that otherwise available, and whether this information leads to a change in management that is ultimately beneficial to the person taking the test13. Are the results of any study applicable to the application for which the test is being used? Are the test results likely to yield valuable information? Ultimately, are people better off if the test information is acted on compared to when it is not?

The value of an accurate test will be undisputed when: the target disorder, for example food intolerance, if left alone without using information from the test, is more detrimental to the individual than if the test results are used; the test has acceptable risks; and effective treatment or action based on the test results exists.

Conclusion

Overall, the public requires guidance as to what constitutes best practice. Before embarking on using a test or testing service, put together a check list to ensure that the test on offer meets the following guidelines:-

Author Bio: Dr. Gillian Hart is a Scientific Director for YorkTest Laboratories Ltd. YorkTest specialise in creating allergy and food intolerance tests. For more information visit http://www.yorktest.com or call 0800 074 6185.

Category: Health/Wellness
Keywords: food intolerance test, self diagnostic test, home testing,