A modified Apt test: a new look at an old test

This study was designed to verify the applicability of a modified Apt test to blood stains on cloth and to determine whether the time of testing affects the accuracy of the results. We collected cord blood samples from full-term newborns (n = 35) and venous blood samples from gravid females (n = 30) and applied them in a random fashion with a cotton swab to standard cloth diapers. A blinded investigator applied an alkali solution to each stain and recorded either color change or no color change. In addition, a time course was performed by applying infant (n = 4) and adult (n = 4) samples to a cloth diaper at an initial starting point and varying the time of the performance of our modified test in intervals up to four hours. Thirty-four of 35 infant samples had no color change, and 29 of 30 adult samples had an easily identified color change. The time course revealed that the samples were indistinguishable after 30 minutes had elapsed. Therefore, a modified Apt test can be used successfully to differentiate between adult and infant blood stains of nonstool origin, only if performed within 30 minutes of the time the stain is produced. This restriction is significant in the emergency department setting.