Thanks, Malcolm. I figured enzyme-IATs. For fun, a trip down memory lane....I'm so ancient that when I first started in the mid-60s as a child prodigy at Canadian Red Cross BTS (now Canadian Blood Services) in Winnipeg, Canada, where the BTS was (and still is) a combined blood donor centre and transfusion service for the entire city, we used capillary tubes to determine ABO and Rh groups, but also for antibody screening (IATs, enzymes, saline) For enzymes, I believe the order was serum, enzyme, rbc suspension, then invert and stick the capillary tube into plasticine on a special box with a back light, let sit, and read with a magnifying glass. Quite often index fingers would get punctured (enough to draw blood) as some cap tubes were jagged. All this a "good grief" to today's workers. Prehistoric paper by Brits evaluting the capillary method: http://tinyurl.com/3sj2lar Cheers, Pat UA: http://www.ualberta.ca/~pletendr/ TraQ: http://www.traqprogram.ca/