A rapid pregnancy test without using urine? Not so fast.

The rapid assessment of pregnancy status is important in urgent health care settings. Determining if a Tube of blood woman is pregnant or not is necessary to:

  • Determine if symptoms such as abdominal pain, vaginal bleeding, and/or vomiting are due to pregnancy;
  • Prevent fetal exposure to sources of radiation (x-ray, CT, scan, etc);
  • Prevent the administration of teratogenic medication.

In many health care setting, qualitative urine hCG testing is often used to quickly determine a woman's pregnancy status. Several posts on this blog have discussed the limitations of this type of testing (see here and here for some background). We have often advocated for the use of quantitative serum hCG testing over qualitative urine testing for this purpose but there are some logistical challenges with quantitative serum testing:

  • The use of a blood sample requires its collection and transport to a central laboratory.
  • Once received in the lab, a blood sample has to be centrifuged to separate the serum (the liquid part of the blood that is actually tested) from the blood cells.
  • Both of the above steps increase the amount of time needed to perform the test and report the result to the physician.

Although many qualitative hCG tests used in health care settings can be used with either urine or serum, qualitative serum testing is impossible to perform at the point-of-care. This is because obtaining serum requires centrifugation of the whole blood and centrifugation can't practically be done outside of a laboratory.

Recognizing that hCG tests performed on blood samples are generally better than thosed performed on urine, physicians are sometimes tempted to use whole blood (instead of serum) as the sample type for qualitative hCG testing at the point-of-care. An example of this type of use is described here.

That report describes the use of whole blood instead of urine or serum for the qualitative detection of hCG in a patient with a ruptured ectopic pregnancy. This was what I call a VBI: a Very Bad Idea. It is so wrong that two colleagues and I wrote to the journal that published the report to let them know it was a VBI.  Basically, we pointed out that:

  • Using whole blood instead of serum or urine was a modification of the intended use of an FDA-approved test and as such was against the law without appropriate validation experiments.
  • The peer-reviewers and journal editors failed to recognize that their report was in conflict with federal and state regulations and the report's publication essentially recommends the promotion of an unauthorized practice with serious patient safety risks.
  • Involving laboratory professionals to help identify solutions for clinical dilemmas involving laboratory tests is always a smart idea.

In response to our criticism, the authors replied with this:

"Physicians' judgment is relied upon to determine when benefit to the patient outweighs the risk of inaccuracy of unapproved use."

In other words they essentially said "we can do anything we want, regardless of regulations, when we act according to our best judgement."

How convenient. How utterly ignorant. How potentially dangerous.

Sadly, this type of mis-information is widespread. A website called "Emergency Physicians Monthly: The Indpendent Voice for Emergency Physicians" featured an article titled "Stat Pregnancy Test…Without Urine?" in September 2013. This article encourages the use of using whole blood for qualitative hCG testing and even provides a "Quick Trick" section on how to perform the test. This is grossly negligent on their part. I note that under the "Tips" section the author writes:

"Be sure to wait at least 5 minutes when using whole blood in the kit. It sometimes takes a while." (emphasis is mine)

Hmmmm, might someone want to define what "a while" is?

I think my opinion on this matter is evident. If reliable results are to be obtained and utilized for patient care decisions, clinical laboratory tests must be performed using validated methods (including the type of sample tested). To deviate from established protocols without guidance from laboratory professionals is a VBI.

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