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.
Apply several drops of whole blood (instead of urine) into the pregnancy test cassette. In the photo, 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? A quick Google search reveals that Accutest, Cardinal Health, ICON, OSOM, and Rapid Response all are approved for both. The question is whether this will work for whole blood. Recall that serum is the extracellular component of whole blood.
One study in the Journal of Emergency Medicine by Dr. Fromm from Maimonides Medical Center looked at exactly this issue(1). 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 nine of 425 pregnancies. Interestingly, the urine pregnancy test was also negative in five of those nine and not performed in the other four.
Believe a positive test. Confirm all tests with a urine qualitative test or quantitative serum beta-HCG.
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.
1. Fromm C, Likourezos A, Haines L, Khan AN, Williams J, Berezow J. Substituting whole blood for urine in a bedside pregnancy test. J Emerg Med. 2012 Sep;43(3):478-82.
2. Habbousche JP, Walker G. Novel use of a urine pregnancy test using whole blood. Am J Emerg Med. 2011 Sep;29(7):840.e3-4.
more on the web
Content for this column taken from
Michelle Lin, MD
Editor-in-Chief of Academic Life in Emergency Medicine
Methotrexate for Ectopic Pregnancy
ACOG Practice Bulletin No. 94: Medical management of ectopic pregnancy. Obstet Gynecol. 2008;111(6):1479-85.
• 2% of all first-trimester pregnancies and 6% of all pregnancy-related deaths
• Risk factors:
- Prior tubal, pelvic, or abdominal surgery
- Genital infections leading to pelvic inflammatory disease
- Prior ectopic pregnancy
- In utero exposure to diethylstilbestrol (DES)
- History of infertility
- Use of assisted reproductive technologies (in vitro fertilization)
- Tobacco use
• Dihydrofolate reductase inhibitor – inhibits DNA synthesis, repair, and cell replication
• Overall success rate for treating ectopic pregnancy = 71-94%
• Success rate of single-dose MTX for B-hCG > 5,000 mIU/mL = 85.7%
Side effects: Abdominal pain, nausea/vomiting, stomatitis
Eligibility criteria for MTX in ectopic pregnancy:
• High clinical suspicion or confirmed ectopic pregnancy,
• Hemodynamically stable,
• Unruptured mass,
• Able to comply with close follow-up
• Normal creatinine, liver transaminases, WBC, hematocrit, and platelet counts
Contraindications for MTX in ectopic pregnancy:
• Overt or lab evidence of immunodeficiency
• Alcoholism, alcoholic or chronic liver disease
• Preexisting blood dyscrasias or significant anemia
• Known sensitivity to MTX
• Active pulmonary disease
• Peptic ulcer disease
• Hepatic, renal, or hematologic dysfunction
• Gestational sac > 3.5 cm on U/S (relative contraindication)
• Embryonic cardiac motion on U/S (relative contraindication)
• MTX 50 mg/m2 IM on Day 1
• Measure B-hCG on Days 4 and 7
• Check for 15% B-hCG decrease between days 4 and 7
• Measure B-hCG weekly until nonpregnant level
• If B-hCG dose not decrease by >15% as expected, re-dose 50 mg/m2 IM and repeat B-hCG on days 4 and 7 after 2nd dose.
Alternative regimens: Two-Dose and Fixed Multidose regimen
(consider for BhCG level > 5,000 mIU/mL)
>>from the comment stream
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!
-Brian Rike, DO
… 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?
-Daniel Lakoff, MD
I have not implemented formally. I am 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.
-Michelle Lin, MD
Response letter from Dr. Christian Fromm, first author of the cited study, Substituting Whole Blood for Urine in a Bedside Pregnancy Test
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 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.