Intended for healthcare professionals

Rapid response to:

Education And Debate

Evidence based diagnostics

BMJ 2005; 330 doi: https://doi.org/10.1136/bmj.330.7493.724 (Published 24 March 2005) Cite this as: BMJ 2005;330:724

Rapid Response:

Use established methods for evaluating diagnostic methods

I agree with Gluud & Gluud that all diagnostic tests must be evaluated as good as the therapeutic methods. However, the history of such evalutations is long and a lot of references could be cited. Especially the approved recommendations (1986) from the IFCC should be followed.(1)

I also agree that "phase III" and "phase IV" studies should be done, but such studies usually meet a considerable conservatism among not only clinicians but also administrators.

When a new diagnostic method is developed the aim is to improve the diagnosis by using a different technique. The new method is assumed to rely on a more specific and reliable biochemical and physiological basis than established methods and hence it is supposed to improve the diagnostic situation, e.g. by establishing a diagnosis earlier and hence in a stage where it can be treated more successfully than now.

"Phase III" and "Phase IV" studies must therefore include not only the aim of the method but also the biochemical basis.

According to the IFCC rules all diagnostic methods in the test should be standardized to the same specificity, i.e. 97,5 %. Then the sensitivity is evaluated according to the results of the tests. For each method the result can be positive or negative. Reject all cases where the two methods yield concordant results (positive or negative) and make a binomial test on P=0.5 for discordant results.

The method yielding significantly more positive results is better than the other(s) (2).

References:

1. Solberg HE. (Part 6: Dybkjaer R, Solberg HE):Approved recommendations (1986) on the theory of reference values. Part 1-6. J Clin Chem Clin Biochem 1987;25:337-662

2. Öhman S et al: Comparisono of seven formulae and isoelectrofocusing for determination of intrathecally produced IgG in neurological diseases. Ann Clin Biochem 1992;29:405-10

Competing interests: None declared

Competing interests: No competing interests

29 March 2005
Sten Öhman
director
Antivenena AB, Evastigen 9, S-590 71 Ljungsbro, Sweden