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.
Thanks George. I will ask for any documenatation from our r
Thanks George. I will ask for any documenatation from our reference lab. A four hour stability is certainly not reference lab friendly for any assay. Coag stability certainly has evolved over the years. I remember collecting these samples in school back in the dark ages and we put them in a dixie cup filled with ice chips. Even the instrument had a chilled rack for storage.
Joe, I’ve sent messages to several of the folks at LabCorp a
Joe, I’ve sent messages to several of the folks at LabCorp and Quest, and have received one response, based upon which, I assume they have run internal validations on PTT stability that have satisfied state and CAP assessors. I’ve noted that ARUP hews to the H21-A5 standard of four hours stability. I’m not sure if this helps you deal with your local physicians, however it seems you could request documentation from your reference laboratory that will help you set or modify your specimen management policy. Geo.