Propanil is an aniline herbicide that is widely used for rice cultivation, but is also used for self-poisoning. Toxicity from propanil is largely due to methemoglobinemia. In resource-poor settings, the capacity to determine methemoglobin concentration is insufficient and prevents effective case management, which results in increased deaths from propanil poisoning.

Blood with a methemoglobin concentration greater than 15% of total haemoglobin levels appears brownish in colour. We introduced a colour reference chart that can be used to semiquantitatively determine methemoglobinemia. Each ward in three rural hospitals received a chart. Ward staff, medical officers and trainee doctors were given a presentation describing the test method and how it should be used with the relevant national treatment guidelines.

In three rural hospitals in Sri Lanka, 401 patients were admitted with a diagnosis of propanil poisoning before the introduction of this test (2003–2007) and 262 patients after it was introduced (2008–2014), 46 of 663 patients died.

The chart can be freely produced with any good-quality colour printer. In three rural hospitals, deaths from propanil poisoning fell from 10% of those admitted with this diagnosis in 2003–2007 (38/401) to 3% (8/262) in 2008–2014 and the use of methylene blue increased from 10% (13/136) to 55% (59/107) over this period.

This simple bedside test was associated with increased use of the first line treatment for propanil poisoning and improved survival. In 2011, the test was included in the national guidelines for the management of propanil poisoning.