Trick of the Trade: Urine pregnancy test without urine

Trick of the Trade: Urine pregnancy test without urine

2016-11-11T18:45:11+00:00

pregnancy_tests_in_bulkEPR
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

Both the urine (top) and whole blood (bottom) of the patient was tested on a qualitative pregnancy test kit. After placing several drops of urine or blood in the sample (S) well, a visible bar appeared at the test (T) line similar to the control (C) line result for both, which indicates a positive pregnancy test.

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)

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]

Expert Peer Review

Thank you so much for your interest in our article, Dr. Lin. To date we have not formalized a process through our laboratory department. Similar to your shop, we use whole blood to make time-sensitive clinical decisions and then try to confirm. But in light of all the recent interest – I have received several inquiries about this matter (I suspect due to the popularity of this blog!) - I am considering taking this the next step, and I will keep you abreast of any developments.

I should like to add some detail to your discussion of the cases in which there were discrepancies between the urine or whole blood POC tests and the quantitative serum hCG testing. You correctly point out that the whole blood testing missed 9 out of 425 pregnancies and that the urine test was also negative in 5 of those (those 5 hCGs were 5, 16, 18, 47, and 50). Keep in mind that the test is intended to be 100% sensitive only for hCG >25, so that probably explains the false negatives for 3 of them, but is somewhat troubling that both the urine and whole blood missed the hCGs of 47 and 50.

On that point, we do know that false negative urine pregnancy testing can occur in the presence of high levels of hCG variants [please refer to the very interesting recent article by Dr. Richard T. Griffey: “Hook-Like Effect” Causes False-negative Point-of-Care Urine Pregnancy testing in Emergency Patients. J Emerg Med 2013;44(1)155-160], but I’m not sure how likely that is to be the case here with such low hCG values.

As you point out, the urine test was simply not performed due to oversight in 4 of the other discrepant cases in which the whole blood tests were falsely negative, so we will never know if the urine would have missed those too, but I suspect the urine would not have picked those up either because of the low hCG values, which were 6, 9, 12 and 22 (all below the test’s threshold of 25).

There were no discrepant cases in which the whole blood test was negative but the urine test was positive. However, there were two discrepant cases in which the urine tested negative but the whole blood was positive (those hCGs were 83 and 159). So, according to our data, there is a suggestion that the whole blood may actually be more sensitive than urine, but that might require a larger sampling to establish.

Dr. Christian Fromm
Assistant Professor of Emergency Medicine, Maimonides Medical Center

Expert Peer Review

ALiEM\'s Bottom Line is spot on -- believe a positive test. When we first discussed this technique in our paper, it was in the context of a fascinating case -- vomiting, no abdominal pain, breast-feeding a newborn, and having just eaten sushi -- except profoundly hypotensive and very ill appearing. This technique allowed us to confirm what seemed like an unlikely diagnosis at the time very quickly, and get to her the OR with OB-Gyn. We\'ve received criticism from our paper from several pathologist PhD\'s (none of which are physicians nor clinicians) that our test was not FDA-approved, but we see incredible value in this technique, regardless of its official use with serum vs. whole blood; we echo the second part of the Bottom Line: use an approved confirmatory test.

Dr. Graham Walker
Assistant Clinical Professor, UCSF. Emergency Medicine Physician, Kaiser San Francisco.

Michelle Lin, MD
ALiEM Editor-in-Chief
Academy Endowed Chair of EM Education
Professor of Clinical Emergency Medicine
University of California, San Francisco
Michelle Lin, MD
Michelle Lin, MD

Latest posts by Michelle Lin, MD (see all)

  • Wow. That is such a neat trick!
    Too bad it is not 100% sensitive but still can be very useful.

  • I agree – this is one of my all-time favorite tricks. It so makes sense that I wish I thought of it.

  • That’s amazing. Would it be okay to post this on my blog? I’ll obviously link heavily to you regarding it…

    @Stella – think you’ll find its not 100% sensitive with urine either!

    • Yes, you are welcome to post on your blog. Thanks for asking.

      • Issay

        Hi just wanna ask if how long does the serum will evaporate? Because serum is more concentrated than urine… just wondering how long shall I wait in able to get a valid result . In urine usually 3 to 5 minutes what about the serum? Beyond that posible you will get a evap line . I got a positive result on my serum pt but I’m not sure if is valid because I saw the fainted 2nd line after 15 or 20minutes. Best thing to do is do they test again. But I’m just curious . Thanks

        • Not based on any literature but on my anecdotal experience, I usually see the positive line at about 5 min.

  • Great idea could have used this a few years ago when an 18 year old female patient presented unresponsive with a positive FAST exam and hypotensive – we got a urine after cath but, this would have been easier to just use blood sample. She did fine but still less pucker time!

    • I sooo love this trick as well. Would have saved me a lot of angst of waiting in the past.

  • I agree – this is one of my all-time favorite tricks. It so makes sense that I wish I thought of it.

  • Anonymous

    I have tried this a gotten all positives but urine and lab blood tests are negative. Which do i trust?

    • Weird results. I suppose I would trust the urine and serum tests, I suppose. That is a bit odd though. Do you know what brand of urine preg test kits you are using? All that I have checked thus far have been approved for urine AND serum qualitative testing.

  • Anonymous

    Several different brands. Ept, clearblue, dollar tree etc… I had my tubes tied so I NEED to know ha! Is there somewhere I could email you the pics?

  • Daniel Lakoff

    A little late to the discussion, but we’re trying to implement Whole-Blood HCG testing as a Department, and are running into the not “FDA-Approved” barrier. Has anybody else discussed with Lab/Pathology departments about this?

    • Michelle

      I have not implemented formally. We are using only in very time-sensitive, active scenarios (hypotensive young woman whose chief complaint is abdominal pain and vag bleeding). We also get a standard urine pregnancy test or serum beta-hcg as a confirmatory test. Let me know if you have any luck with this!

  • Michelle

    From Dr. Christian Fromm (first author of first citation):

    Thank you so much for your interest in our article, Dr. Lin. To date we have not formalized a process through our laboratory department. Similar to your shop, we use whole blood to make time-sensitive clinical decisions and then try to confirm. But in light of all the recent interest – I have received several inquiries about this matter (I suspect due to the popularity of this blog!) – I am considering taking this the next step, and I will keep you abreast of any developments.

    I should like to add some detail to your discussion of the cases in which there were discrepancies between the urine or whole blood POC tests and the quantitative serum hCG testing. You correctly point out that the whole blood testing missed 9 out of 425 pregnancies and that the urine test was also negative in 5 of those (those 5 hCGs were 5, 16, 18, 47, and 50). Keep in mind that the test is intended to be 100% sensitive only for hCG >25, so that probably explains the false negatives for 3 of them, but is somewhat troubling that both the urine and whole blood missed the hCGs of 47 and 50.

    On that point, we do know that false negative urine pregnancy testing can occur in the presence of high levels of hCG variants [please refer to the very interesting recent article by Dr. Richard T. Griffey: “Hook-Like Effect” Causes False-negative Point-of-Care Urine Pregnancy testing in Emergency Patients. J Emerg Med 2013;44(1)155-160], but I’m not sure how likely that is to be the case here with such low hCG values.

    As you point out, the urine test was simply not performed due to oversight in 4 of the other discrepant cases in which the whole blood tests were falsely negative, so we will never know if the urine would have missed those too, but I suspect the urine would not have picked those up either because of the low hCG values, which were 6, 9, 12 and 22 (all below the test’s threshold of 25).

    There were no discrepant cases in which the whole blood test was negative but the urine test was positive. However, there were two discrepant cases in which the urine tested negative but the whole blood was positive (those hCGs were 83 and 159). So, according to our data, there is a suggestion that the whole blood may actually be more sensitive than urine, but that might require a larger sampling to establish.

  • J D

    There is a letter to the editor (attached) that discusses the use of whole blood on urine HCG POC kits. Please see attached.

    https://www.evernote.com/shard/s243/sh/896c0dd6-ea54-4054-8246-5be3f5fe5b45/22fb9f141ea22ed250fe6f42cc997259

  • Joyce

    Interesting, this would have helped me when I presented to the er with iud and left lower quad. Pain. Was sent home after urine hpt was neg. pain got intense went to another hospital that drew blood and hcg level was 200. Ectopic preg and tube burst.

  • LF

    This link is being posted in pregnancy forums and ladies are pricking themselves at home, dripping blood on home pregnancy tests and saying it works to show a positive pregnancy. Can you clarify that whole blood is not just blood you prick yourself with at home and that this isn’t reliable to do yourself, that it has to be done by a medical professional? Thank you!

    • Michelle Lin

      Wow thanks for letting me know. First and foremost this described technique is a nonstandard approach for diagnosing pregnancy using these kits. This is solely to be used an emergency. Furthermore this post is meant for solely medical professionals who can draw whole blood and not just fingerstick blood. These are two types of different bloods. Please do NOT use this trick if you’re not a medical provider who understands the nuances of this technique. Thank you again for alerting me to this problem. Feel free to share this comment with the appropriate people.

  • Janae

    Why even post this then if you can’t even do it ? That makes no sense especially if doctors are the only ones that can do it

  • Glen

    So how do you get the blood…prick myself with a needle

    • No this is only meant for a medical setting and a true blood draw by a medical professional. Needlestick doesn’t count