When LoQ Cannot Be Determined

The module warns when the fitted power model does not cross the CV% acceptance threshold inside the tested concentration range. The callout leads with that fact, then explains the most likely reason for this dataset:

All CV% values are below the threshold (most common)

If every measured CV% across all concentration levels is already below the acceptance threshold, the power model predicts the LoQ would lie below the lowest tested concentration. Because the LoQ falls outside the range of data, the model cannot reliably locate it. This does not necessarily indicate a problem — it may simply mean the method performs well throughout the tested range. To resolve this:

–Test lower concentration levels to extend the range downward toward the expected LoQ.
–If the method is known to perform well at all tested concentrations, consider whether the CV% threshold is set appropriately for the clinical application — a lower threshold may better reflect the precision requirements of the test.

All CV% values are above the threshold

If every measured CV% exceeds the acceptance threshold even at the highest tested concentration, the power model predicts the LoQ lies above the tested range. To resolve this:

–Test higher concentration levels where CV% is expected to be lower.
–Investigate whether the method has a fundamental precision problem at low concentrations — consult the manufacturer and review instrument maintenance and calibration records.

Flat or inverted CV%-vs-concentration relationship

If CV% barely changes across levels, or rises as concentration increases, the power-model intersection is unstable and may fall outside the tested range even when the threshold sits near the observed CVs. Raising the CV% threshold usually does not fix this. Redesign levels so precision is meaningfully worse at low concentrations and improves below the threshold at higher concentrations, and confirm measured results track the assigned values.