Helen Murray Free with her husband and scientific collaborator Alfred in 1955 Credit: BAYER Helen Murray Free, who has died aged 98, was the co-developer, with her husband Alfred Free, of Clinistix, the first dip-and-read diagnostic test for diabetes and for monitoring glucose levels in urine, an achievement that revolutionised diagnostic testing. Before the introduction of Clinistix in 1956, laboratory technicians tested for diabetes by adding a reagent to urine in a test tube and then heating the mixture over a Bunsen burner, a process that was not only cumbersome but also imprecise because it could not distinguish glucose from other sugars. Working at Miles Laboratories in Indiana, the Frees worked out how to impregnate thin strips of filter paper with chemicals that changed colour based on the concentration of glucose present in the urine, the intensity of the resulting blue-green depending on the amount of peroxide, and hence, glucose, in the sample.