Sol capture immunoassay kit and procedure

An immunoassay procedure for detection of analytes in urine wherein an immunological reaction is conducted in an aqueous phase containing the urine and a filterable immunocomposite containing an inherently colored gold sol particle is formed if the assay is positive. The colored, gold sol particle containing immunocomposite is collected for direct visual observation on a filter element. False positive readings are minimized by (1) removing contaminants from the urine to prevent clogging of the filter element and non-specific binding of unreacted reactants thereto by contacting the urine with a porous contact element having a detergent material dispersed on its external and interstitial surfaces; (2) preventing non-specific binding of unreacted immunoreactive substances to the filter element by blocking the latter with polyvinyl pyrrolidone; and/or (3) including a green dye material in the aqueous reaction phase to improve the optical distinction after washing the collection filter between negative and positive results on the filter.