Today's post is by a guest author, Ian Schwartz, M.D. Dr. Schwartz is an assistant professor of emergency medicine at the Yale University School of Medicine and the former medical director of the adult emergency department at the Yale-New Haven Hospital in New Haven, CT. Here, he provides his perspective on determining a patient’s pregnancy status in an emergency setting and describes the possible consequences of erroneous hCG test results.
The practice of emergency medicine is a daily challenge for providers in the field. Patient histories are varied and nuanced and no two cases are ever the same. In the hectic, chaotic and over-flowing hallways of the emergency department (ED), providers (not surprisingly) look to hang on to objective evidence in order to come up with diagnoses and treatment plans.
Experienced providers realize, of course, that a diagnosis is usually a best guess. For the majority of patients, emergency room doctors are simply synthesizing a few facts and ideas into a coherent explanation for the symptoms that brought the patient to the ED.
The challenge is that even those elements that we call facts are, themselves, nuanced. Every ED doctor has had the experience of staring at a chest x-ray and debating whether the patient had pneumonia or some fluid in their lungs. X-ray interpretation is literally dealing in shades of grey.
As opposed to evaluating X-rays, laboratory test results would appear to be much more objective. The lab provides a discrete test result along with a reference interval for defining what is considered to be “normal.” For most health care providers the validity and accuracy of most test results go unquestioned. Yes, that patient absolutely has elevated calcium. Yes, this patient is anemic. Decisions for further testing, treatment and disposition are often made based solely on these test results.
Emergency providers (and others who practice evidence-based medicine), think in terms of odds and probability. That is, they think about the likelihood of a disease. Some examples: the likelihood of a blood clot in the lungs given a patient’s risk factors or the 30-day likelihood of a heart attack if a patient with chest pain is sent home. Each ED doc has his or her own acceptable “miss rate” for a given condition.
However, when it comes to pregnancy testing that sort of calculation and prediction simply doesn’t enter the mind of most ED providers. The pregnancy test is often considered to be the one single binary (yes/no) test that they can actually rely on.
Most emergency departments perform qualitative hCG tests using a urine sample to determine a woman’s pregnancy status. The tests are similar to those that can be purchased over-the-counter and performed at home. The person performing the test will be handed the urine sample, perform the test, and (hopefully) chart that result into the medical record and (hopefully) alert a nurse or other care provider of the result.
A provider sees this result and takes the appropriate action. There is usually no second thought about the quality of the test result. If it’s negative then the patient with abdominal pain is not pregnant and the physician can get the CT scan of the abdomen instead of the ultrasound. A negative result is also a license to order antibiotics, pain medications, and other drugs without concern for possible fetal harm. The urine hCG test is the standard way we define pregnancy in the emergency department and it gives the green (or red) light to treat the patient as not pregnant (or pregnant).
There is a problem with this type of reliance: the urine hCG test, itself, is simply not good enough to tell us whether or not a patient is pregnant.
Here are a few facts that most ED providers are unlikely to know about hCG testing:
- hCG appears in blood before urine, sometimes up to 5 days earlier.
- The claimed analytical sensitivity of most qualitative urine hCG tests is 25 IU/L whereas the quantitative blood assays are sensitive to 1-2 IU/L (commonly pregnancy is defined by greater than 5 IU/L).
- Even though common qualitative urine tests claim 99+% accuracy in determining pregnancy status, a recent study suggests that they are actually only 99% sensitive at an hCG concentration of 150-225 IU/L.
- There is a potential window of 3 to 7 days during the first trimester of pregnancy where a quantitative blood test will detect hCG while the qualitative urine test might not.
- Ectopic pregnancies can occur at hCG concentrations below what is detectable by current qualitative methods.
- In one study of over 11,700 urine samples, 69 (0.5%) of ED hCG test results were erroneous due to documentation errors, inherent deficiencies in qualitative tests or because the hCG concentration was below the level of detection.
So what are some real-world consequences of not using the most accurate hCG test at our disposal? If we believe a patient with abdominal pain is not pregnant (when in fact they are) we order CT scans of the abdomen looking for appendicitis or other abdominal diseases. That CT scan just delivered 10 mSv of radiation to the mother and fetus and doubled the risk of the fetus developing a childhood cancer (1 in 1,000). Or we just ordered Motrin, a medication known to cause neural tube defects and a variety of heart defects. And we have just increased the risk of miscarriage two and a half fold.
In a later post, I will address the erroneous belief that qualitative urine hCG tests are quicker to result than quantitative blood tests. However regardless of speed, ED’s across the country are utilizing a test that does not deliver the accuracy that most providers believe they are getting. This is a fact that should be quite troubling to all of us considering the number of urine pregnancy tests that performed each day. How many erroneous results are we are unknowingly receiving and what is the potential harm that is being done to a fetus in its most fragile period of growth?