AmniSure: The effect of blood on ROM diagnosis accuracy of PAMG-1 and IGFBP-1 detecting rapid tests.

Babett Ramsauer, Wiebke Duwe, Bettina Schlehe, Regina Pitts, Dirk Wagner, Katja Wutkewicz, Dmitry Chuvashkin, Harald Abele and Robert Lachmann.
Journal of Perinatal Medicine. 2015; 43(4): 417-422

Research shows that conventional diagnostic tests, such as nitrazine (pH), ferning, pooling and ultrasound can be inaccurate and invasive. In fact Neil 2010^[1] shows that 47% of the time clinicians are not confident in their diagnosis of PROM based on history and examination alone. The current biomarker tests to aid in detection of PROM give clinicians the certainty they need to make a confident diagnosis, quickly and easily.

Recent meta-analyses of published literature has also shown that the PAMG-1 based test AmniSure out performs those tests based on IGFBP-1 in an unknown (clinically relevant) population.^[2] However, to date, there has been no research evaluating the two tests in a population presenting with signs of vaginal bleeding. Given that there is presence of PAMG-1 and IGFBP-1 in maternal blood, vaginal bleeding could impose on accurate diagnosis.

This prospective, observational, multi-site study aimed to compare the diagnostic performance of the PAMG-1 test (AmniSure) with the IGFBP-1 test, for the diagnosis of membrane rupture in patients with equivocal membrane status. The study compared the performance of both tests in the presence of light and heavy vaginal bleeding.

The patient sample (n=151 ranging from 10.5-41.0 weeks of gestation) was acquired from 21 German hospitals, from small birthing facilities to large University hospitals. The patients were randomly recruited presenting with non-obvious membrane rupture and evidence of vaginal bleeding presenting with signs, symptoms or complaints suggestive of ROM with no obvious leakage of fluid from the cervical os during speculum examination. Patients with no vaginal bleeding or a clinically visible rupture of membranes were excluded from this study.

The sensitivities of the PAMG-1 and IGFBP-1 tests in patients with blood admixtures (this study) compared with the sensitivities of patients with equivocal ROM but without vaginal bleedings. The sensitivity of IGFBP-1 seems to be higher in patients with blood admixtures, possibly due to an artefact related to the exclusion of 11% of all IGFBP-1 patients due to results that were difficult to interpret (Figure 3).

The author’s found that the differences in specificities and positive predictive value (PPV) to be statistically significant. The IGFBP-1 test specificity decreased by 12.8 percentage points to a value of 75% whereas the PAMG-1 (AmniSure) test only decreased by 7 percentage points to a value of 91.5%. Showing that while the presence of vaginal bleeding impacts both tests the IGFBP-1 is much more affected than the PAMG-1 test. In fact, the specificity of AmniSure in the presence of blood (91.5%, this study) is greater than that of the IGFBP-1 test without vaginal bleeding (87.8%, this study) (Figure 4).

In conclusion, the presence of vaginal bleeding in a women presenting with uncertain ROM diagnosis seems to have a greater impact on the biomarker test for IGFBP-1 than on the performance of AmniSure.

AmniSure is recommended by RANZCOG guidelines in the diagnosis of term PROM.

Will you consider AmniSure as the first test you turn to for confirmation of your ROM diagnosis?