From Joe Lamb, St. Francis Hospital, Columbus, GA: Hi George. Recent updated test directories for the two big reference labs that serve local physicians state the specimen stability for partial thromboplastin time (PTT, APTT) is 24 hours at room temperature. This causes much confusion when we reject a specimen more than four hours old for PTT testing. Did these guys do their own studies? Who’s right, the Clinical and Laboratory Standards Institute (CLSI) or the Big Guys?
Hi, Joe, and thanks for alerting me to this apparently new requirement. I checked the “Big Guys’” web sites and confirmed your statement, which seems to contradict standard H21-A5 that limits the PTT to four hours’ room temperature storage. I’ve forwarded your question to several colleagues to see if they have some new data. You have to admit, 24 hours, if correct, is a lot better than 4 hours! Geo.