Ten Commandments of diagnostics

Ten Commandments of diagnostics
A long long time ago, in a galaxy far far away (well in 2012), Richard Lehman published a spectacular blog – the ten commandments of new therapeutics
These stood the test of time and are still pertinent today
This was blog was then turned into a BJGP article
Ten Commandments for patient-centred treatment

It’s a modern classic of Evidence Based Medicine and should be on everyone’s desk

At the time of the original blog, in a moment of lunchtime grumpiness, I put together a parallel set of commandments for diagnostics
I don’t have delusion that these carry the same gravitas as the original authors – but I feel they carry the same themes but applied to diagnosis.
Michael Power from Newcastle then fleshed them out and the final paper is here

The original set are reproduced below

There are various versions of this kicking around the t’interweb biblified and non biblified.

Ten Commandments of diagnostic Testing


  1. Before you order a test, remember that “All tests can do harm. Many tests do good. Some tests do more good than harm”.
  2. know the predictive positive value and predictive negative value of the test before you order it.
  3. know that if thou dost order a test with a positive predictive value below 50%, you might as well toss a coin.
  4. know the prevalence of the disease in the population from which the person you are going to test comes from; for combined with positive predictive value or negative predictive value, you can then ensure that you have interpreted the result properly. Recognise that in a low-prevalence population, even a very sensitive has poor predictive value, and if you order such a test, you might as well toss a coin.
  5. know exactly what you will do with the result of the test before you order it. “If you don’t know what to do with the result, or if the test be not part of an evidence-based pathway, then DESIST from ordering such a test.”
  6. know the cost of the test intend to order, before you order it, and also enquire whether there be cheaper ways of finding the same result.
  7. know who has in the past ordered, or might in the future order, the same test under the same set of circumstances, and then ensure that they know that they do but waste resources, since you have performed the same already before. Therefore, record the result of the test which thou dost order very clearly that all others might see it.
  8. inform patients that “shinier scanners and swizzier kits” might well give better resolution pictures, but might not actually change a clinical management decision.
  9. simply not ask or order patients to undertake diagnostic tests for which there be no evidence of proven benefit.
  10. explain to the patient, clearly and without bias, that which the test can and cannot tell you, and ask them if they are content to proceed.


Greg Fell, Consultant in Public Health, NHS Airedale Bradford and Leeds

With thanks to Anne Connolly, GP and Toni Williams Public Health SpR Bradford.

Anna Sayburn, Senior Editor, Best Health, BMJ Evidence Centre

Bibliification – Ash Paul, Medical Director, NHS Bedfordshire.








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