Bioequivalence and Bioavailability Forum

Dear LCMSMS!

❝ Is there any relationship between the intercept of the linear equation and

❝ LLOQ area ratio values?

No, although the area ratio at LLOQ is expected to be > intercept...

When we are applying in regression model to our data, we are mainly interested in calibration (statisticians call this 'inverse regression' x = (y - a)/b).
In a linear function y = a + b*x, the intercept a is just one of the two parameters defining the model. On the other hand the intercept gives us a number describing the average response y at x = 0, i.e., at the 'blank'.

❝ Is there any regulation in this regards?

Yes, see the guideline page (not only the FDA, but other contries as well).

LLOQ in bioanalytics is defined as the minimum concentration which can be quantified with acceptable accuracy and precision. This presents a major difference to analytical methods in environmental analysis, because were are lucky enough to have access to blank matrices.
So we really have to demonstrate the suitability of LLOQ for at least 6 replicates during validation.
Regulators don't want to see any statistical approach defining the LLOQ (i.e., from the calibration curve itself) - although there are some nice methods available (Fisher's Information Criterion, for example).