Pyrogen testing at a turning point – On occasion of the 30th anniversary of the whole blood monocyte activation test

The whole blood pyrogen test was first described in this journal exactly thirty years ago. Its variant based on cryopreserved blood followed one year later. Together with other monocyte activation tests (MATs), it has fundamentally changed the landscape of pyrogen testing. In the five years since the 25th anniversary article in this series, progress has been remarkable: The European Pharmaco­poeia deleted the rabbit pyrogen test (RPT) effective January 2026, ending a 55-year era; ISO 10993-1:2025 removed material-mediated pyrogenicity from mandatory evaluation endpoints for medical devices; the U.S. FDA updated its guidance on pyrogen testing; and the MAT market grew to over $600 million. New validation studies have demonstrated MAT equivalence to the RPT for both endotoxin and non-endotoxin pyrogens, and the first product-specific MAT validations have been accepted in regulatory filings in Europe and the United States. Reporter cell lines and tran­scriptomic approaches are opening next-generation detection capabilities. Yet implementation gaps persist: The MAT is still underutilized for blood transfusions, cell therapies, and airborne pyrogens. Recombinant alternatives to the Limulus amebocyte lysate assay (LAL) have finally achieved phar­macopeial recognition, addressing horseshoe crab conservation concerns. This article reviews the developments of the last five years, updates the lessons learned, and reflects on three decades of bringing a human cell-based test from the laboratory bench to global regulatory acceptance. Plain language summary Thirty years ago, a simple idea emerged: Instead of injecting rabbits to check medicines for dan­gerous fever-causing contaminants, why not use a drop of human blood in a test tube? That idea became one of the monocyte activation tests (MAT), and this article takes stock of how far the field has come. The progress has been remarkable: Europe officially retired the rabbit test in January 2026 after 55 years. New validation studies have proven the MAT works at least as well as the rabbit – and often better, catching contaminants that the rabbit test routinely misses. Yet important gaps remain. The MAT is still underused for blood transfusions, cell therapies, and airborne contami­nants. Some countries have yet to accept it. The story of the MAT is ultimately one of good science slowly, stubbornly winning, and the work is not finished yet.