Mar 29 2014
From Rose Markarian, Supervisor Hematology, Saint John’s Health Center, Santa Monica, CA: Hi George, We perform Stago’s confirmatory hexagonal phase Sta-Clot LA test for lupus inhibitor testing. We validated Stago’s recommended cut off value of ≤ 8.0 seconds several years ago when the test was implemented. Do we have to validate the cut off value with each new lot of reagent? Please advise.
Hi, Rose, I forwarded your question to Dave McGlasson, who did some of the early Sta-Clot LA work, and he asserts that you should validate the 8-second limit with each new lot of reagent, and also that the cutoff may vary among instruments. Dave’s comment appears below.
Comments (2)
Lupus Anticoagulant
An additional expert writes that Rose should refer to CLSI E
An additional expert writes that Rose should refer to CLSI EP26. Good laboratory practice dictates that a new lot should be validated prior to putting into use. If their studies indicate the current cutoff is still resulting in expected results they are OK. If not, they need to re-establish a new cutoff.
Rose, thanks for your question. We found that the 8-second c
Rose, thanks for your question. We found that the 8-second cutoff was determined on the old ST4 single channel Stago system. Our facility was one of the first to figure out how to automate that assay. See Charles LA, McGlasson DL et al: Blood Coagulation and Fibrinolysis, 1994, 5: 601-4. We used an MLA 900 which was a photo-optic system. The method then described by Stago for establishing the cut-off was to run at least 25 normal specimens and take the delta value of 4 SD’s from the mean of the LA1 LA2. Surprisingly ours was around 5 seconds. The photo-optic system picks up the clot faster than the mechanical system. Therefore your cut-off really depends on the instrument you are using. This became more evident over the years when I was working with other facilities with different lots of reagents and other instrumentation on comparison study protocols. Each facility had different lots of the reagent. They were surprised that our positive cut-off values were different. Therefore, I would advise performing this running protocol when you get a new lot of the reagent. Contact your Stago hotline on this issue for their current recommendation.