Lars - see Walmsley and White "A Guide To Diagnostic Clinical Chemistry"3rd
Edn. Page 15 or many other sources.
For a 95% probability that two results in a patient are different they must
differ by more than 2.8 SD. This SD is the combined SD for analytical and
intra-individual variation i.e. SD(total) = SQRT[(SD analyt)squared + (SD
intra-individual)squared].
Critical difference at 95% probability = 2.8 x SD(total).
This gives a figure which is statistically significant, whether it is
clinically significant depends very much on the specific clinical
situation. I do not believe that it is possible to set up a general table
of "clinically significant" differences for each analyte. For most
analytes it is possible to think of situations where a specific degree of
change in one patient would be unremarkable whereas in another it would
highly significant and require immediate changes in management.
Bruce Campbell
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Bruce Campbell FRCPA FAACB
Sullivan Nicolaides Pathology
Ph 61 (0)7 3377 8672
Fax 61 (0)7 3870 5989
Email [log in to unmask]
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