An integral multilayer analytical element in which a first fibrous porous layer, a nonfibrous porous layer, and a second fibrous porous layer superposed in this order on a water-impermeable light-transmissive support the first fibrous porous-layer having a larger pore size than the nonfibrous porous...http://www.google.com.au/patents/US5393493?utm_source=gb-gplus-sharePatent US5393493 - Analytical element for whole blood
