Trick of the Trade: Urine pregnancy test without urine

pregnancy_tests_in_bulk
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 cassette. In the photo below, the patient was pregnant with a serum beta-HCG level of 250 mIU/mL whose urine and whole blood qualitative tests were both positive.

PregWholeBood

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, Cardinal Health, 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. The whole blood testing approach missed a total 9 of 425 pregnancies. Interestingly, the urine pregnancy test was also negative in 5 of those 9 and not performed in the other 4.

Bottom Line

Believe a positive test. Confirm all tests with a urine qualitative test or quantitative serum beta-HCG.

Tip

  1. Be sure to wait at least 5 minutes when using whole blood in the kit. It sometimes takes a while.
  2. Do not apply additional drops of water or saline to the whole blood sample. This causes unnecessary dilution. Just wait for the blood to osmose across the entire test strip.
  3. This is trick is ONLY for medical professionals and not the lay public. We are discussing an actual blood draw and not a simple cut on a finger to obtain blood.

Another example courtesy of Dr. Joe Habboushe (New York Hospital–Queens of Cornell University) and Dr. Graham Walker (Stanford) 2 :

Pregnancy1
Time: 1 minute
Pregnancy2
Time: 5 minutes

S = Sample well; T = Test specific (will show bar if +HCG); C = Control (will always have a bar)

 

References

  1. Fromm C, Likourezos A, Haines L, Khan A, Williams J, Berezow J. Substituting whole blood for urine in a bedside pregnancy test. J Emerg Med. 2012;43(3):478-482. [PubMed]
  2. Habboushe J, Walker G. Novel use of a urine pregnancy test using whole blood. Am J Emerg Med. 2011;29(7):840.e3-4. [PubMed]

Paucis Verbis: Methotrexate for ectopic pregnancy

Ectopic pregnancy methotrexate

Ectopic pregnancies account for as many as 18% of patients who present with first-trimester bleeding or abdominal pain in the Emergency Department. This Paucis Verbis card summarizes the 2008 American College of Obstetricians and Gynecologists (ACOG) guidelines on the use of methotrexate (MTX) for ectopic pregnancies. Not all ectopic pregnancies require operative management.

What are the indications and contraindications to MTX? When should they follow up with their obstetrician?

Answer: In 4 days for a repeat b-HCG and possible second dose of MTX

Note that one of the eligibility criteria is that the patient must have an “unruptured ectopic pregnancy”. Many would consider that any ultrasonographic evidence of free fluid may be a sign of an early rupture. It is left up to clinician judgment in how “unruptured” is interpreted.

PV Card: Methotrexate for Ectopic Pregnancy


Adapted from [1]
Go to ALiEM (PV) Cards for more resources.

Reference

  1. ACOG Practice Bulletin No. 94: Medical Management of Ectopic Pregnancy. Obstetrics & Gynecology. 2008;111(6):1479-1485. doi: 10.1097/aog.0b013e31817d201e
By |2021-10-11T15:53:39-07:00Nov 11, 2011|ALiEM Cards, Ob/Gyn|
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