Study disputes accuracy of some brands of home pregnancy tests

Some kits fail to detect hormone if test is done early in the pregnancy

Health & Fitness

April 25, 2004|By Maja Beckstrom | Maja Beckstrom,Knight Ridder / Tribune

Walk down a pharmacy aisle and you'll see these words on almost every home pregnancy kit -- "ready to use first day of missed period" and "more than 99 percent accurate."

But it turns out the vast majority of brands detect only 16 percent or fewer of pregnancies if they are used as early as recommended, according to new research. Only one test is sensitive enough to detect 95 percent or more of pregnancies when used so early.

"There is no incentive for the manufacturers to make them more accurate," said Lawrence Cole, professor of obstetrics and gynecology at the University of New Mexico at Albuquerque and author of the study, which appeared in the American Journal of Obstetrics and Gynecology. "All they care about is selling them, and they're selling just fine."

Researchers at the National Institutes of Health developed the first home pregnancy test in the early 1970s. Though the tests' technology has improved in the past 25 years, the basic concept remains the same.

Home kits detect the hormone human chorionic gonadotropin -- hCG -- in urine. An embryo releases hCG just a few days after conception. After the embryo attaches to the uterus, the concentration of hCG in a woman's body doubles every two days.

Cole, a leading researcher on hCG, became interested in home pregnancy tests after hearing about negative test results from women who actually were pregnant.

"People call and say, 'I can't understand it, my home pregnancy test said I wasn't pregnant, and I was,' " Cole said. "I was fed up with hearing about it."

Levels were too low

For the study, Cole and his colleagues measured the amount of hCG in the urine of 25 pregnant women on the first days of their first missed periods and tested 18 brands of home pregnancy tests to determine how well they detect those levels of hCG.

Though their levels of hCG varied widely, most levels were too low for most tests to detect. Only First Response Early Results, which sells for about $12, would detect more than 95 percent of pregnancies.

Only three of the 18 tests produced a positive result when testing urine that contained the amount of hCG typically present during the second day after a woman's first missed period. By the third day, eight tests appeared effective.

"If one waits a week after the missed period," said Cole, "any home pregnancy test will do."

The Target brand, which promises "unsurpassed accuracy" for $3.89, is among the least accurate, Cole said. It is manufactured for Target by Inverness Medical, which makes nearly identical kits for CVS and Walgreens.

In a subsequent, still unpublished study, Cole and his colleagues found, on the first day a woman misses her period, First Response and Clearblue Easy identified 95 percent and 80 percent of pregnancies, respectively.

All other tests seemed capable of diagnosing pregnancy in, at most, only 16 percent of early users.

Another reason for the failure to detect early pregnancies, Cole said, is most tests are designed to detect a regular form of hCG rather than a recently discovered variant present in early pregnancy.

Claims termed misleading

So how can manufacturers claim the tests are 99 percent effective? A small asterisk on the test packaging refers consumers to a notation saying the claim is based on "typical" hormone levels. Cole says the claims are misleading.

A Food and Drug Administration spokesman said manufacturers are required only to prove their test kits are as effective as a previously sold test kit to make that claim -- but there is nothing preventing them from using a 1970s test as a comparison.

"I didn't write the law. I only follow it," said Steven Gutman, a doctor and director of the FDA office of in vitro diagnostics. He said Cole's research has sparked "some internal discussion" at the FDA about ways to craft "more appropriate language."

Meanwhile, the research findings may change the recommendations some health-care providers give their patients.

Diana Saari, an obstetrician-gynecologist with the University of Minnesota-affiliated University Specialists in Minneapolis, said she now will be recommending First Response to people who want an early answer.

"It's really depressing," she said. "I had no idea most were this bad."

Saari said it is not uncommon for pregnant patients to come in saying they had a negative result on an early home pregnancy test.

"In the past, I'd look askance at that," Saari said. "I thought they had gotten their last menstrual period inaccurate. I had relied on the sensitivity of those tests being over 90 percent. I always thought it was the patient's mistake. And now I realize that is not the case."

So what is a woman to do?

Clearly the most sensitive tests are First Response and Clear Blue. The research also suggests that waiting 10 minutes to read the result rather than the recommended one to two minutes improves accuracy and makes test results easier to make out.

"I'd tell my patients that if they get a negative result but they still have breast tenderness and fatigue and their suspicion is high, they should take another test," Saari said. "And while you're waiting, don't start swigging the scotch."

Tell your pregnancy test story

Share your experience with a home pregnancy test on the National Institutes of Health Web site "A Thin Blue Line."

Compiled for the test's 25th anniversary, the site contains history, interviews with researchers, scientific background, advertisements from early pregnancy test kits and a place to anonymously add your story to an archive at George Mason University in Virginia.

Visit www.history.nih.gov / exhibits / thinblueline.

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