Category: Obstetrics

Whole Blood Works For POC Pregnancy Tests

If there is such thing as a “cult favorite” article amongst Emergency Physicians, right now, this probably qualifies as the one receiving its 15 minutes of fame on Twitter.

If there is any singular agony known to all Emergency Physicians it is the inability to obtain urine samples in a timely manner.  Sometimes, this is for the urinalysis.  Other times, this is for the qualitative pregnancy test result.  If only there were a better way….

And, perhaps, there is.  This is a two year study of sensitivity/specificity of the POC pregnancy test using the Beckman Coulter ICON 25 – comparing the performance of using urine vs. whole blood, with laboratory quantitative bHCG >5 as the gold standard.  95.3% sensitivity for the urine test, 95.8% sensitivity for whole blood, with 100% specificity.  Most of the false negatives were due to beta hCG < 100.

Interesting alternative!

“Substituting whole blood for urine in a bedside pregnancy test”
http://www.ncbi.nlm.nih.gov/pubmed/21875776

Sometimes, The Pregnancy Test Lies

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