A couple years ago, my hospital pulled the POC urine pregnancy tests from the ED because of false negatives – leading to incredulous discussions of how it was possible for a nursing assistant to screw up something so simple as a dichotomous colormetric test.
Well, at Washington University, when they had multiple issues with their POC pregnancy test, they investigated the issue in more depth, and this nice little article is an overview of the limitations of the the test. There are two ways the POC test fails:
– Not pregnant enough.
– Too pregnant.
We all know about sensitivity in early pregnancy really only being 97% or so at one week, and no one will fault the test for that. However, their case series of five patients, all of whose serum hCG was >130,000, are hypothesized to have saturated the reagent to the point of a false-negative test.
In any event, interesting article about something I hadn’t put much thought into.
“‘Hook-Like Effect’ Causes False-Negative Point-Of-Care Urine Pregnancy Testing in Emergency Patients”
http://www.ncbi.nlm.nih.gov/pubmed/21835572