|*****NOTE = The ROM Plus test replaced AmniSure in 2014*****]
To: Ervin B. Shaw, M. D., Director of Anatomic Pathology
From: John B. Carter, M. D., Director of Clinical Pathology
Subject: January 16 meeting of Maternal/Child Department Physicians
Date: January 16, 2008
Memo in which three topics were presented:
AmniSure test:We have done a brief in-the-lab validation study of the AmniSure test for PROM at the request of several obstetricians. (This is keeping in
line with our policy of confirming or challenging vendor claims for test performance.) A small sample of 22 patients, those from whom specimens were collected by L&D
nurses during December 2007, noted 9 patients positive for PROM by discharge chart review; 13 patients to be negative for PROM. Of the 9 "positive" patients, the
AmniSure test was positive in 7 -- a 20% false-negative rate. The currently used waived nitrazine test for pH 7.0-7.5 of amniotic fluid had a similar false-negative rate. The waived ferning test by low-power microscopy was positive in only 30%
of positive patients tested -- a 70% false negative rate.
Of the 13 "negative" patients, all AmniSure and nitrazine tests were negative. The Ferning test had one false-positive result.
While the AmniSure vendor literature claims a 99% sensitivity rate, our small sample of patient tests could not confirm this. While there are some clinical advantages (swab test rather than speculum collection, and a more objective read-out), the need for strict performance and quality control of this moderate complexity test entails a $130/test reagent cost. The AmniSure test would be performed in the laboratory, 3-shifts, most likely as one of the Body Fluid Analysis tests, and is not technically difficult or work-intensive to perform.
The OB physicians were of mixed opinion, one noting that the test had been voted down at RMH. The decision was left in their hands to get back to us.
Fetal fibronectin test: results of the evaluation of the Fetal Fibronectin test were presented:
51 patients were tested from October 9 to December 13;
46 were reported as normal and none of these patients delivered within the 14 days following testing. The only positive patient on which we were able to obtain follow-up delivered a stillborn infant two days after testing. The other 4 positive patients were transferred.
Thus there appears to be real clinical value to fibronectin testing as a predictor of false vs. true labor, an outcome that we noted 12 years previously when initially offering the test through LML, though the test was ordered only by Dr. Fitzgibbon and we ceased offering the test due to lack of use upon his retirement. Interestingly, a couple obstetricians noted that they were doing the fibronectin test in their office.
Rh typing test: weak-D (Du) typing of Rh-negative patients:
Since resumption of testing for weak-D Rh antigen on Rh-negative patients last summer, 2 of 326 Rh-negative patients have typed as positive for weak-D (Du) antigen. This low percentage of weak-D (Du) positivity reflects the significantly increased sensitivity of RhD anti-sera compared with previous years in which Rh-negative Du positive patients were a reasonably frequent finding. [discussion of Du issue HERE]
In addition to Dr. Stallard's index patient, who we typed as Rh-negative (Weak-D/Du not tested) who claimed she had "always been Rh-positive", two other obstetricians at the meeting noted that they had had an Rh typing discrepancy. Other obstetricians expressed unawareness that we had not been doing "Du" typing. All members present were supportive of the idea that we continue to routinely test Rh-negative patients for weak-D/Du antigen, and we plan to do so, though not repeating the test once the result was documented and on file.
Committee response to this presentation and to our lab services was strongly positive.
(posted 19 January 2008; a link added 9/25/09; addition 11/17/2014)