Trick of the Trade: Urine pregnancy test without urine

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.

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

Be sure to wait at least 5 minutes when using whole blood in the kit. It sometimes takes a while.
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.
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 :

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

References

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]
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]

By Michelle Lin, MD|2020-12-04T13:15:41-08:00Apr 10, 2012|Expert Peer Reviewed (Clinical), Ob/Gyn, Tricks of the Trade|

Trick of the Trade: Fluorescein eyedrops

This is a guest post by Dr. Ian Brown (Stanford):

The Roberts textbook describes the procedure of corneal fluorescein staining as touching a moistened fluorescein strip to the cornea. Maybe it is an irrational fear of a paper cut to the sclera, or a fear of touching an already abraded cornea with the paper, but I try to find an alternative. I have seen physicians hold the eye open with one hand, hold the fluorescein with a second hand and then drip tetracaine on the paper and let it drip into the eye with a third hand. I, unfortunately, only have two hands.
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By Michelle Lin, MD|2019-01-28T23:36:28-08:00Mar 27, 2012|Ophthalmology, Tricks of the Trade|

Trick of the Trade: Pelvic speculum for peritonsillar abscess

Peritonsillar abscess drainage in the ED continues to be one of my favorite procedures to perform. There are several tricks to increase your chances for a successful aspiration. One trick involves using a curved laryngoscope to help depress the tongue AND provide a bright light source.

What if you don’t have a laryngoscope readily available?

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By Michelle Lin, MD|2019-01-28T23:36:17-08:00Mar 20, 2012|ENT, Tricks of the Trade|

Trick of the Trade: Irrigation fluid is key – but not in your eye!

High pressure irrigation of wounds is critical in reducing the rate of wound infection. There are a variety of commercial irrigation kits which include splash guards. If you are irrigating correctly and generating at least 8 PSI of pressure, some irrigation fluid should splash up and out of the wound. Be careful not to splash irrigation fluid in your eyes.

What if you don’t have a commercial irrigation setup?

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By Michelle Lin, MD|2026-06-16T16:02:49-07:00Mar 13, 2012|Tricks of the Trade|

Trick of the Trade: Another magnet trick for metallic FB removal

Last week, I talked about the use of Rare Earth Magnets for removing metallic foreign bodies. Sometimes a straight magnet though isn’t quite strong enough to grab a metallic foreign body. If only you had a small magnetic hemostat.

This week Dr. Catherine Perry (Culpepper Memorial Hospital) and Dr. Kolapo DaSilva (PGY-2 at UVA) emailed me with a creative solution. They encountered a patient with a BB pellet lodged deeply in the soft tissue. Small mosquito clamps couldn’t get around the BB. A cardiac magnet alone caused the BB to tent the skin up.

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By Michelle Lin, MD|2019-01-28T22:25:49-08:00Mar 6, 2012|Tricks of the Trade|

Trick of the Trade: Rare earth magnets for metallic FB removal

NasalFB

A child presents to your Emergency Department with a small button battery up her nose. Your usual tricks fail:

Occluding the other nostril and having the mother blow in the patient’s mouth forcefully.
Using a small curette or forceps to scoop or pull it out.

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By Michelle Lin, MD|2026-06-16T16:02:51-07:00Feb 28, 2012|Tricks of the Trade|

Trick of the Trade: Difficult intubation — making lemonade out of lemons

In many cases of massive GI bleeding, airway control is essential. During endotracheal intubation, suction sometimes just isn’t adequate enough to allow to get a good view of the vocal cords. The pool of blood keeps re-accumulating faster than you can suction. You think you see an arytenoid, pointing you in the direction of the trachea, and so you slide the endotracheal tube in.

Unfortunately, when you bag the patient, you realize that you are in the esophagus.

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By Michelle Lin, MD|2016-11-11T18:51:16-08:00Jan 31, 2012|Tricks of the Trade|