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Myths in Emergency Medicine: Sense and Sensitivity Ectopic Pregnancy and Beta hCG

May, Natalie MBCHB, MPHE

doi: 10.1097/01.EEM.0000499533.27241.77
Myths in Emergency Medicine

Dr. Mayis a specialist in emergency medicine with paediatric emergency medicine in the UK and a registrar in prehospital emergency medicine in Sydney, Australia. She writes regularly forhttp://StEmlynsblog.org. Follow her on Twitter @_NMay, and read her past articles athttp://emn.online/MythsEMN.

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Our colleagues in gynecology are quick to remind us that pregnancy is not a disease state. While this is true, it is the duty of the diligent emergency physician to consider whether pregnancy might be the underlying condition contributing to, confounding, or accounting for presentations to the ED in women of childbearing age.

Pregnancy is not a disease, but ectopic pregnancy certainly is, one that carries a considerable mortality (five percent of maternity-related deaths in developed countries [Lancet 2006;367(9516):1066]) and morbidity (reproductive potential is sometimes affected; around eight to 15 percent of women go on to have another ectopic pregnancy. (Clin Obstet Gynecol 2012;55[2]:455.)

Ectopic pregnancy rates are estimated at one to two percent of spontaneous conceptions. (Arch Gynecol Obstet 2013;288[4]:747.) There are multiple factors (sexually transmitted diseases, pelvic inflammatory disease, assisted reproductive therapies) that increase the likelihood of implantation outside the uterus, but it is always possible that a woman may present with the condition without any discernible risk factors.

Before rupture and obvious clinical signs of hemodynamic compromise, women may present with vague signs and symptoms such as vaginal bleeding, cramping abdominal pain, and fainting. How do we determine, then, whether an ectopic pregnancy is present? If we assume that all women are pregnant until proven otherwise, how exactly do we prove otherwise?

If you are sufficiently skilled in ultrasound you might be able to rule the pregnancy in, but as with so much of our EM practice, it's a reliable rule-out we are after. (Ultrasound Obstet Gynecol 2016;47[1]:28.) Our patients will tell you it's simple: Do a pregnancy test.

Pregnancy tests used in the ED vary by geographical region but can be divided into two separate methods of measuring beta human chorionic gonadotropin (b-hCG). Home pregnancy tests consist of urine measurement of b-hCG. Some EDs use these as point-of-care tests while other institutions send urine to the lab for testing. Spoiler: Most laboratories use exactly the same point-of-care home pregnancy test as you would in the ED. Other departments use serum testing, reporting a positive or negative result, or a quantitative b-hCG.

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Pregnancy Test's Value

The problem comes when we try to translate what is essentially a quantitative measurement into a binary, qualitative outcome. What makes a pregnancy test negative?

Urine pregnancy tests are heterogeneous and their reliability depends to a degree on the manufacturer. Clarke and Shawkat performed a shortcut review in 2011 and found a variation in sensitivity between 87.5 and 100 percent for urine b-hCG measurement. (Best Evidence Topics 2011; http://bit.ly/2ajH2To.) A more recent comparison of four assays by Kamer, et al., found concerning proportions of false-negatives, particularly at low levels of b-hCG. The limit of detection of b-hCG by urine pregnancy tests means that it is possible some women with low levels of b-hCG might not be correctly identified. (Clin Biochem 2015;48[6]:448.)

So what's the value of a urine pregnancy test? If it's not sensitive enough to satisfy me that there isn't an ectopic pregnancy present, does it have some specificity value? Perhaps. A positive urine pregnancy test can be very helpful in facilitating the patient's journey, but if the patient is sick enough, the test is usually unnecessary (as is waiting for a urine sample), and if she is not compromised, it's likely a quantitative b-hCG will be useful for her ongoing care. It's worth considering whether skipping the urine test altogether actually makes financial sense, too.

Herein lies the problem. Even if you shun urine pregnancy testing in favor of serum (which you probably should if sensitivity is your aim), there is no upper level at which an ectopic pregnancy is completely ruled out. Studies have suggested that ectopic pregnancy is actually more likely with lower levels of b-hCG. (Acad Emerg Med 2003;10[2]:119.) Then there are the terrifying case reports of two women presenting with ruptured ectopic pregnancy, with b-hCG levels <10IU. (J Reprod Med 2007;52[6]:541.) That's enough to abolish my bravery in using b-hCG as my single rule-out strategy at all.

So what should we do with these patients in the ED? It is helpful to have an agreed departmental approach to identifying ectopic pregnancy, ideally one with which your gynecology colleagues agree.

  • You should resuscitate the hemodynamically compromised patient. Consider a RUSH protocol ultrasound examination. (Emerg Med Clin NA 2010;28[1]:29.) Free fluid in the abdomen can facilitate rapid transfer to the operating room, even before a pregnancy test has been taken.
  • Risk-stratify women who are not actively bleeding or who are hemodynamically stable but have high-risk features. A negative pregnancy test and a negative ultrasound will significantly reduce the probability of an ectopic pregnancy, but serial assessment is the safest way forward. Ensure appropriate return for assessment by gynecology in the clinic and make sure the patient knows to return to the ED if a change in condition occurs. My preference in performing a pregnancy test is serum b-hCG. It makes more sense to opt for greater sensitivity.

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