How are fill-volume defects (high, low, empty) identified in vials?

Fill-volume defects are deviations in the amount of product in the container. The three types are high volume (overfill), low volume (underfill), and empty components.

Fill defects are graded major to critical because an under- or over-dose affects the delivered dose and an empty unit is a clear process failure. They are identified by comparing the fill line against a defined acceptance range, which trained inspectors and automated systems judge against reference standards. Container colour, meniscus shape, and solution clarity all affect how easily a fill deviation is seen, so challenge units are matched to the real product.

FTI includes high-volume, low-volume, and empty-component units in its challenge sets so fill-level qualification is built into inspector and machine qualification, not treated as a separate check.