Reference ranges

 Most people are comfortable with the idea of reference ranges, but what do actually tell us, or rather don’t tell us? To create a reference range a number (usually over 120) of volunteers are matched for factors (table 1) and the analyte is measured. Firstly, most ranges have a 95% confidence which means that the top 2% of values and the bottom 2% of values are omitted, so it is possible to be healthy but outside the reference range, you are just at the very top or the very bottom which aren’t shown. Secondly, you should use ranges from invalidated sources with great care as ranges can vary with age and sex for example.

Table 1 shows common attributes which are matched to create, or can affect a reference range.