A 25 year old woman presents to the Emergency Department having syncopized in the waiting room, where she was triaged with the chief complaint of abdominal pain. Ectopic pregnancy immediately bubbles to the top of your differential diagnosis.
The patient is too dizzy to walk to the bathroom to give you a urine specimen to check a urine pregnancy test. Plus, she admits that she just urinated in the waiting room bathroom a few minutes ago - so no urine now.
Trick of the Trade
Apply several drops of whole blood (instead of urine) into the pregnancy test casette
Did you know that most urine pregnancy test kits are approved for both urine and serum samples? On a quick Google search, I found that Accutest, ICON, OSOM, and Rapid Response all are approved for both. The question is whether this will work for whole blood.
One study (1) in the Journal of Emergency Medicine by Dr. Fromm from Maimonides Medical Center looked at exactly this issue. Whole blood pregnancy test performed extremely well, especially if positive:
- Sensitivity 95.8%
- Specificity 100%
- Negative predictive value 97.9%
- Positive predictive value 100%
In their study, very low beta-HCG values (<159 mIU/mL) occasionally yielded a false negative for whole blood pregnancy tests. It missed 9 of 425 pregnancies.
Bottom line: Believe a positive test. Confirm with a urine test or quantitative beta-HCG.
Tip: Be sure to wait at least 5 minutes when using whole blood in the kit. It sometimes takes a while. See the photos, courtesy of Dr. Joe Habboushe (New York Hospital–Queens of Cornell University) and Dr. Graham Walker (Stanford).
Time = 1 minute
Time = 5 minutes
S = Sample well
T = Test specific (will show bar if +HCG)
C = Control (will always have a bar)