Assay method for whole blood samples

A method for detecting the presence of a member of a specific binding pair ("sbp member") in a whole blood sample, said sbp member selected from the group consisting of ligand and homologous receptor, where said method involves (1) a binding agent for red blood cells in said sample;

• (2) a solid bibulous element to which is bound at least one sbp member;
• and (3) a signal producing system capable of producing a detectable signal, the members of which include at least one label which is bound to an sbp member, said method comprising:
• (a) combining in an aqueous medium a whole blood sample, a binding agent for aggregating red blood cells in said sample, and fewer than all the members of the signal producing system,
• (b) contacting a portion of said bibulous carrier with said aqueous medium to allow said medium to diffuse along said bibulous element and said aggregated red blood cells to concentrate in an area on said element adjacent the air/liquid interface,
• (c) contacting said bibulous element with any remaining members of the signal producing system, and
• (d) detecting the signal as a result of said signal producing system, wherein said signal is related to the amount of said sbp member in said sample.

A kit for use in a method for determining an analyte in a whole blood sample, said analyte being a member of a specific binding pair ("sbp member") selected from the group consisting of ligand and homologous receptor, which method comprises--

• contacting in an aqueous medium (a) a bibulous element, at a predetermined region of said element, said element having an sbp member substantially uniformly bound to the surface thereof with (b) said whole blood sample and (c) a binding agent for red blood cells present in said whole blood sample;
• whereby said medium traverses said element to define a border related to the amount of analyte and said red blood cells aggregate at a region on said element corresponding to the air-liquid interface;
• and
• determining said border by means of a signal producing system, which system includes a labeled sbp member;
• said kit comprising in a packaged combination in predetermined ratios for combination with said sample according to said method,
• (a) a binding agent specific for said red blood cells,
• (b) a bibulous element to which is bound at least one sbp member, and
• (c) a signal producing system capable of producing a detectable signal in relation to the amount of analyte present in said sample.