VendorInvestigate result on a Suzhou liraglutide lot lands 4.2 points below the supplier’s figure

Two laboratories analysing vials from the same liraglutide lot have returned figures 4.2 percentage points apart. VendorInvestigate reported 98.9%; Medutest reported a lower number on a shallower gradient with a tighter integration threshold. Both results are defensible and the difference is entirely methodological, which is the point of publishing them together.

Reported figures across the set were: highest 98.9%, lowest 95.8%, median close to the midpoint of the two. Every report in the set stated a detection wavelength, and 10 of them stated an integration threshold. The Journal has asked the laboratory to publish thresholds on all reports as a matter of routine.

Discrepancies of one to two percentage points between a supplier’s figure and an independent determination are common and usually explicable: a faster gradient resolves fewer impurities, a higher integration threshold discards more small peaks, and a wider solvent-front exclusion window removes early-eluting fragments from the calculation altogether. None of that is misconduct. All of it is invisible unless the method is disclosed.

Rowena Ashcombe, community pharmacist and diabetes educator, said the gap was predictable from the methods alone. "You can reconstruct almost the whole difference from the integration threshold. What you cannot reconstruct is why anyone thinks a number without a threshold is comparable to a number with one."

QST’s dossier has been updated with this determination and with the date of the request for comment. The dossier’s "what we could not verify" box records the questions still outstanding.