Blood is known widely by healthcare professionals as an accurate, reliable sample type for pregnancy testing.
You might be wondering, “What’s wrong with peeing on a stick?”
Urine pregnancy tests are not “wrong,” but blood has shown less susceptibility to some of the issues that are seen with urine hCG tests.
Why Use a Blood Pregnancy (hCG) Test?
Think about a typical process for a woman wondering if she’s pregnant. In general, she might take a urine test (or three) at home. If that test comes back positive, she’ll schedule a doctor’s visit. When she gets to the doctor’s office, they’ll more than likely give her a urine pregnancy test. If that test comes back positive, they will generally draw blood and send off for a confirmatory, blood-based pregnancy (hCG) test result.
Why would they send off for blood? Can’t they trust the results from the urine tests? Truth is, blood is often used by doctors when they need to be sure of a pregnancy diagnosis because blood-based hCG tests aren’t as susceptible to the problems outlined below.
Issues With Urine Pregnancy Tests
Urine-based tests are facing increasing attention due to false negatives. Why does this happen? Well, it can get technical very fast (and I’m not a laboratorian), but I’ve broken down the top reasons below. See my previous post for more:
- Higher limit of detection for urine tests vs. blood tests. In other words, blood-based tests can be more sensitive.
- Beta core fragments. These are present in urine and can cause interference and false results. Read this for more.
- The “hook effect.” At a certain point in a woman’s pregnancy, hCG spikes up severely and the extreme level of hCG can actually overwhelm the test lines, causing a false result. Dr. Ann Gownowski has an excellent blog called The Pregnancy Lab and has written extensively about female reproductive health, and specifically issues with pregnancy testing today.
- Diluted urine. Most of you probably already know to check for pregnancy in the morning. Urine can become diluted and therefore the hCG levels may not be detected if a women is early in her pregnancy. The time of day does not matter to a blood-based pregnancy test.
How Big is This Issue?
Getting a get a “false result” can have huge implications, depending on the treatment the woman is about to receive. Any false result is not good, but false negatives are particularly concerning. Consider a woman being admitted for a scheduled surgery. They will test her for pregnancy to be sure it’s safe to do the surgery. Some procedures can be harmful or even fatal to a developing fetus. It’s critical that early pregnancy cases are detected before these procedures are completed.
University of Kentucky Validation Study
Robert Nerenz, PhD, DABCC, a well-respected and widely-published author in the field of women’s health, completed third-party field evaluations at the University of Kentucky to confirm the accuracy of NOWDiagnostics’ easy-to-use technology. The study took place in the Emergency Department and outpatient clinics at the University of Kentucky Medical Center in Lexington.
Principal investigator of the study was Dr. Nerenz, who served as an Assistant Professor in the Department of Pathology and Laboratory Medicine and the Director of Point-of-Care Testing at the University of Kentucky Medical Center. He is now an Assistant Professor of Pathology and Laboratory Medicine and Assistant Director of Clinical Chemistry at the Dartmouth-Hitchcock Medical Center. His recent work has focused on the evaluation of qualitative hCG device performance and the impact of misleading test results on patient care. View the full publication by clicking here.
Currently, POC hCG testing at the University of Kentucky is performed using urine specimens, but urine-based testing is not without flaws, as Nerenz noted in the Journal of Applied Laboratory Medicine report.
“Unfortunately, urine qualitative hCG devices are subject to false negative results in early pregnancy when urinary hCG concentrations fall below the devices’ limit of detection and after week six of pregnancy due to the “hook effect” caused by high concentrations of hCG variants,” Nerenz wrote. “Furthermore, collection of urine often delays testing in trauma patients, dehydrated women or those who choose not to provide a urine specimen out of distrust of medical professionals. As an alternative approach, quantitative hCG measurement in plasma or serum can detect pregnancy earlier than urine-based methods and eliminates the risk of false negative results caused by hCG variants found only in urine.”
The field evaluations validated the ADEXUSDx® test as an acceptable method for point-of-care testing using capillary (finger stick) blood. This is important because samples do not have to be taken using a traditional blood draw and the samples do not have to be transported to a central, complex laboratory.
“Despite its superior analytical performance, quantitative plasma/serum hCG testing has not been widely adopted for the rapid determination of pregnancy status because it requires transporting the specimen to a central laboratory, processing and analysis, all of which contribute to an unacceptably long turnaround time,” Nerenz wrote. “A device that could be used at the POC using a whole blood specimen would harness the benefits of plasma/serum-based testing while providing reduced turnaround time relative to central laboratory testing.”
UCLA Validation Study
A second study validating the ADEXUSDx hCG test was completed at the University of California at Los Angeles (UCLA) and recently published. UCLA tested 283 samples. First, they tested the samples for pregnancy using NOW Diagnostics’ whole blood, point-of-care pregnancy test, the ADEXUSDx® hCG test.
Next, UCLA tested the same patient samples on a lab analyzer. In this case, quantitative total hCG values were obtained from the RochehCG+β2 sandwich assay. The goal was to assess if the new point-of-care test (POCT) could obtain comparable results to the lab analyzer.
” The test would offer improved turnaround time without sacriﬁcing sensitivity or speciﬁcity as compared with a laboratory based immunoassay, which typically has an overnight turnaround time at our institution… In addition, the ADEXUSDx hCG test represents a valuable and unprecedented alternative to a laboratory-based assay in settings where diagnostic and laboratory services are unavailable.”
See this post for more.
ABOUT NOW DIAGNOSTICS INC.
NOW Diagnostics is a leader in innovative diagnostics testing. Its ADEXUSDx® product line features a lab at your fingertip, using only a single drop of blood to test for a variety of common conditions, illnesses, and diseases with results in a matter of minutes. By eliminating the need to send tests to off-site laboratories, NOW Diagnostics has the potential to decrease by days the waiting period to determine test results. The company’s Springdale, Ark., facility was officially registered with the U.S. Food and Drug Administration in December 2014. The company is currently offering an hCG (pregnancy) test in the United States and Europe, and three cardiac (heart attack) tests and three toxicology tests in Europe. Additional tests are in the development pipeline, including sexually transmitted diseases, more cardiac (heart attack), food intolerances, common infectious diseases, and a variety of screening tests. For more information about NOW Diagnostics, visit www.nowdx.com. For more information about the ADEXUSDx® hCG test, visit https://www.nowdx.com/products/hcg.