FDA Warning Letter Criticises Handling of OOS Results at a Contract Laboratory

The U.S. Food and Drug Administration criticises the handling of Out-of-Specification (OOS) results at a U.S.-based contract testing laboratory in a recent Warning Letter. The letter, dated 12 November 2025, was published on the FDA’s website on 02 December 2025 and refers to an inspection conducted in June 2025.

Specifically, the FDA cites the following OOS-related deficiencies:

• Multiple microbiological OOS results were not adequately investigated.
• As a recurring root cause, an “unknown laboratory error” was stated – without sufficient scientific justification.
• The firm relied on retesting without first adequately investigating potential contamination sources.
• The effectiveness of the proposed CAPA was not evaluated.
• The firm lacked a formal, robust OOS management system.

In addition, the agency criticises the overall inadequate quality management. The Quality Unit lacked adequate procedures for deviations, change control and cleaning, and did not ensure effective oversight of laboratory processes. The FDA requests a comprehensive remediation and quality system programme, including an independent retrospective review of all invalidated OOS results for U.S. products over the past three years.

Further information is available in the Warning Letter to Rhyz Analytical Labs published on the FDA website.