Performance Data

AmniSure® is a one-step immunochromatographic assay. Several monoclonal antibodies are used in the test to detect PAMG-1. AmniSure® works within a wide range of PAMG-1 concentrations in vaginal discharge (from 5 ng/ml to 100 µg/ml). The diagnostic accuracy of the test relies on only a miniscule amount of released amniotic fluid.

The clinical performance of the AmniSure® test was determined by three studies where it was compared to clinical diagnosis provided by a combination of routinely used Nitrazine, Ferning and Pooling tests. The diagnosis was set when two out of three control tests gave identical results (2-out-of-3 method). A total of 432 patients were evaluated at different sites. Patient gestational age ranged from 11- 41 weeks. Relative to clinical diagnoses determined by routine clinical tests, AmniSure®’s sensitivity and specificity were estimated as follows:

The test employs highly sensitive monoclonal antibodies that detect even a minimum amount of the protein, which is present in cervico-vaginal discharge after the rupture of the [fetal] membranes. To minimize the frequency of false results, two monoclonal antibodies have been selected to set the sensitivity threshold of AmniSure® at the optimal low level. This level allows the detection of the extremely small quantities of amniotic fluid in vaginal discharge. Background concentration of PAMG-1 that uses this combination of monoclonal antibodies is around 50-220 picogram (i.e. 0.05-0.22 ng) per 1ml of vaginal discharge. The sensitivity cut-off of AmniSure® is 5 ng/ml, i.e. at least 20 times higher than the background concentration. This gap allowed increasing the accuracy of AmniSure®.

As a first step of the test, the vaginal swab is used non-invasively to take a sample of vaginal discharge. The swab is then dipped into a vial with solvent that extracts the sample substance from the swab. Finally, the test strip is inserted into a vial and result can be read within minutes.

The Pad Region of the test strip is dipped into the vial (see CHART). A-MABs in soluble form are located in the Pad Region. These MABs have colloidal gold particles attached to them. When A-antibodies come in contact with PAMG-1 protein, resulting from the rupture of fetal membrane and the subsequent leakage of the amniotic fluid, they “catch” PAMG-1 and transport it to the test region.

The test region of the test strip has B-antibodies immobilized on it. B-antibodies “meet” PAMG-1 bound to A-MABs flowing up from the Pad Region. This “meeting” immobilizes the system of PAMG-1/A-MABs, resulting in a brown/yellow stripe that becomes visible in the test region. This stripe is produced by gold dye attached to A-antibodies and indicates a rupture of fetal membranes.

The second stripe, the one in the control region, has nothing to do with fetal membrane rupture. It is designed to provide indication that the test strip is functioning properly. This stripe appears when rabbit anti-mouse IgG antibody (not shown in the CHART) catches the mouse A-antibody with dye gold. Gold dye gives the resulting stripe its color.