Kastle–Meyer test

[1] In 1901, Joseph Hoeing Kastle and Oliver March Shedd in the U.S. found that biological material could cause the oxidation of phenolphthalin to phenolphthalein in slightly alkaline solutions.

[6] However, in 1908, Pozzi-Escot (who by then was living in Lima, Peru) found that the test produced false positive reactions in response to a number of substances besides blood.

Waiting for periods over 30 seconds will result in most swabs turning pink naturally as they oxidize on their own in the air.

[citation needed] Optionally, the swab can first be treated with a drop of ethanol in order to lyse the cells present and gain increased sensitivity and specificity.

Chemical oxidants such as copper and nickel salts will cause the Kastle–Meyer reagent to turn pink before the addition of the hydrogen peroxide, thus it is vitally important to add the reagent first, then wait a few seconds, then add the hydrogen peroxide.

The phenolphthalein used in this test has been modified from its conventional form, in that it has been reduced by two electrons and is pre-dissolved in alkaline solution.

Donating electrons to hemoglobin converts the phenolphthalin back into the intensely colored phenolphthalein.