Large volume reverse passive haemagglutination greatly increases the sensitivity of the usual RPH assay

A modification of the RPH assay is reported with a much larger volume (LV-RPH) than usual of the analyte (e.g. 10 ml instead of 100 μl or the usual 30 μl). This “affinity-concentration” step produces an increase of sensitivity of the order of 100-fold. Experimental systems investigated were the assay of human chorionic gonadotropin (allowing detection of 5 pg ml−1), of progesterone-BSA conjugate (allowing detection of 10 pg ml−1) and detection of chlamydial antigen and rotavirus increasing the usual detection limit of 1640 to 140,000 or 180,000. It is anticipated that this LV-RPH will be of special value in testing urine and faecal extracts where there is usually no limit in the amount (volume) available.