Questioning the Effectiveness of Preoperative Pregnancy Tests
Preoperative pregnancy testing is a controversial subject. Many anesthesia departments mandate preoperative pregnancy testing before surgery on all patients of reproductive age while others rely on the preoperative assessment to determine the need for pregnancy testing.
The American Society of Anesthesiologists (ASA) Task Force on Preanesthesia Evaluation published an advisory in 2002 that stated pregnancy testing may be considered for all female patients of childbearing age (Practice Advisory for Pre-Anesthesia Evaluation. Anesthesiology 96:485-496, 2002). Clinical characteristics to consider included an uncertain pregnancy history or a history suggestive of current pregnancy. The Task Force recognized that a history and physical examination may be insufficient for identification of early pregnancy.
An updated Practice Advisory for preanesthesia evaluation was published in March 2012. ASA reiterated that the literature was inadequate to inform patients or physicians on whether anesthesia causes harmful effects on early pregnancy. Pregnancy testing may be offered to female patients of childbearing age and for whom the result would alter the patient's management.
In 2013, as part of the Choosing Wisely campaign, ASA reiterated that they did not include pregnancy testing in their top 5 preoperative recommendations of tests to avoid because physicians and hospitals already had the opportunity to set their own practice and policy (October 12, 2013, www.choosingwisely.org). Thus, ASA does not require preoperative pregnancy testing.
A review of the literature reveals that the incidence of detecting a previously unrecognized pregnancy preoperatively ranges from 0.2 to 1.2%. One of the earliest studies that tested women of childbearing age within six days of ambulatory surgery in Chicago detected 7 previously unrecognized pregnancies out of 2056 women tested for an incidence of 0.3%. (Manely et al. Preoperative Pregnancy Testing in Ambulatory Surgery: Incidence and Impact of Positive Result Anesthesiology vol 83 (4), October 1995, 690-693).
A retrospective chart review of preoperative pregnancy testing of adolescent females in Saint Louis revealed an overall positive rate of 1.2% (Azzam et al. Preoperative pregnancy testing in adolescents. Anesth Analg 1996; 82: 4-7).
A more recent article described the experience of an ambulatory surgery center that implemented urine hCG testing for all women of childbearing age on the day of surgery. A retrospective chart review found 5 positive test results out of 2588 women, which is an incidence of 0.2%. Further analysis revealed that 3 were previously unrecognized pregnancies, one was an unrecognized ectopic pregnancy and 1 was a false positive result in a premenopausal woman. The cost of testing to detect one true positive result was calculated to be $3723. (Kahn et al. One-year experience with day-of-surgery pregnancy testing before elective orthopedic procedures. Anesth Analg 2008; 106 (4): 1127-31).
Most preoperative testing for pregnancy has relied on qualitative urine hCG testing using a point of care device. These tests were originally designed to confirm pregnancy after a missed expected menstrual period. These devices generally have cutoffs for positivity that vary from 20 to 50 IU/L, depending on the brand. Because of this limited sensitivity, first morning urine samples are recommended because they are the most concentrated of the day. Urine hCG tests were not intended for preoperative detection of early pregnancy on a random urine sample. Early pregnancies are most likely being missed using this testing strategy.
Quantitative hCG assays performed on blood samples are much more analytically sensitive than qualitative urine assays. Most quantitative hCG assays can detect hCG at concentrations of 0.1 to 2.0 IU/L. Also, hCG concentration is more than twice as high in serum than urine and serum concentration is not affected by fluid intake. Therefore, quantitative assays detect pregnancy earlier and more reliably than qualitative urine assays. Quantitative serum hCG assays are better designed for preoperative detection of early unrecognized pregnancy, but are much more expensive. The cost benefit ratio of preoperative testing with a quantitative assay needs to be calculated.
Based on review of available literature, the following conclusions are warranted:
- Routine preoperative pregnancy testing for all female of childbearing age remains controversial.
- According to the ASA, preoperative pregnancy testing is optional.
- If pregnancy testing is offered, informed consent should be obtained from competent patients and/or parents.
- Urine hCG has been the test of choice preoperative testing, but is not optimal.
- Quantitative hCG testing of serum would be more sensitive but significantly more expensive.
