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Home Diagnostic Tests: The Ultimate House Call?
by Carol Lewis

More and more Americans are playing doctor in the privacy of their own bathrooms, using a few drops of blood or a urine sample to test for cholesterol, blood glucose, or evidence of colon or rectal cancer. In fact, a snippet of a child's hair now can confirm the use of illicit drugs.

Often seen as a less expensive and a more convenient alternative to a trip to the doctor's office, self-testing diagnostic and monitoring devices are booming in sales. Devices such as blood-glucose tests and blood-pressure kits make it easier for people to self-monitor conditions such as diabetes and hypertension. However, this technology-driven trend is not without limits and could result in serious problems for those who rely on the tests instead of on the expertise of their health-care provider. A recent shift in the home diagnostics market--from monitoring chronic illnesses to diagnosing serious or potentially fatal diseases--is raising red flags among health professionals.

For years, pregnancy tests and ovulation predictors dominated the home test kit market. While these devices still generate large numbers of self-care sales, other tools of the medical trade are fast becoming available outside the doctor's office--no prescription needed. Spiraling health-care costs, increased interest in preventive health care, and a desire for privacy are paving the way for products that now include screening for the virus that causes AIDS and for drugs of abuse.

Screening tests often are used at home to check for symptoms of a disease when they may not be readily apparent. For example, people can measure their cholesterol and triglyceride levels--two types of fats in the blood--to help minimize the risk of cardiovascular disease.

Benefits and Limitations
Home test kits are, in many cases, as inexpensive as a co-payment to a doctor and a lot less time-consuming. Some can provide speedy results. Women often use home pregnancy test (HPT) kits for these reasons, as well as for the convenience of testing at home. Some women prefer to know for sure that they are pregnant before visiting their physicians, and HPT kits can help confirm pregnancy earlier. An earlier confirmation provides an opportunity for health-care providers to counsel women about their options, and to discourage potentially harmful behaviors, such as smoking and use of alcohol or drugs.

Kidney disease is one of the most devastating complications of diabetes, but it's also detectable and treatable in its earliest stages. A home test kit allows people with diabetes to test for glucose and even small amounts of protein in their urine--an early sign of kidney dysfunction.

Jim Watson, R.Ph., a pharmacist at the CVS pharmacy in Gaithersburg, Md., says that in his experience, blood glucose monitoring systems and home pregnancy tests are among the most popular tests purchased for home use.

"Diabetics already know they have the disease and so they test their blood sugar levels several times a day," he says. By contrast, Watson says, although women may only use a pregnancy test once, they are still one of the most popular tests the store sells. Sales of both HIV and drug screening home tests are infrequent, according to Watson.

One sign of their overall increasing popularity is the fact that many pharmacists are moving home test kits from behind their counters onto free-standing displays. The lure of the Internet is also helping to make these devices more readily available.

Steven Gutman, M.D., director of the Food and Drug Administration's clinical laboratory devices division, says that consumers need to be wary about buying and using the kits on their own. "People need to carefully read the test-kit labeling and instructions, where important information and warnings about the product are listed," he says. Among other things, this information tells how a test works, and what to do when it doesn't. Home test kits are meant to be an adjunct to doctor visits, not a replacement for them. "Although the menu of home testing products has expanded," Gutman says, "the advice is still the same."

See Your Doctor, Too
While convenience, confidentiality, and the cost-saving benefits of home testing cannot be overlooked, doctors are concerned about the availability of medical tests that encourage self-diagnosis because of the possibility that the results could be misinterpreted and treatment might be delayed.

For example, Sandy Stewart, Ph.D., a research biomedical engineer in the FDA's Center for Devices and Radiological Health (CDRH), says that blood pressure monitors should be used for tracking blood pressure readings between doctor's visits. "Users should never change their medications based on a home blood pressure reading." If there are significant changes, he says, the user should see his or her doctor immediately. "The blood pressure reading taken in the physician's office must be the final word."

In addition, the diagnostic value of home test kits can be affected by users who don't follow instructions carefully. In an effort to conceive a child, Donna Trossevin of Frederick, Md., bought from a local pharmacy an ovulation predictor that uses body temperature to help pinpoint a woman's most fertile time. Although the kit consisted of only a thermometer and special paper to chart her daily temperatures, Trossevin says it was difficult to get accurate readings because "if you don't hold the instrument just so, you can easily misread the numbers." And the half a degree increase from a person's normal temperature that a woman is looking for to predict ovulation "is such a small window of opportunity and easy to miss," says Trossevin. "I just never knew 100 percent whether I was ovulating or not."

Those who rely on home tests also miss out on pre- and post-test counseling, which offer information, support, competence, interpretation, and follow-up advice to consumers that only a health-care professional can give. The benefit of having a health-care professional involved in a test or screening procedure is that the results can be evaluated within the context of the whole health picture, not just one test. Furthermore, receiving news of potential pregnancy, illness, or infection over the phone, or from the color of a test strip, can be devastating.

"The first 72 hours following a positive result for an illness as serious as HIV is when people are most likely to hurt themselves," says Edward Geraty, a licensed clinical social worker with Behavioral Science Associates in Baltimore. Geraty says it's important to have a face-to-face relationship when delivering the news of a positive HIV test. Without it, he says, "there's a psychological component of the person's illness that is completely left out of the process."

Bob Barret, Ph.D., agrees. A professor of counseling at the University of North Carolina at Charlotte, Barret believes that home test kits, particularly for HIV, "are best used only by those who are well-educated about the disease, and who are in touch with their emotions and have a good support system around them."

Find a Reputable Source
Accuracy, too, is an important consideration when it comes to home testing. False positive test results indicate that a condition is present when, in fact, it is not. False negatives are results that do not identify a condition that is present.

The Federal Trade Commission, which enforces consumer protection laws, recently reviewed results of several unapproved HIV test kits advertised and sold on the Internet for self-diagnosis at home. In every case, the kits showed a negative result when used on a known HIV-positive sample.

Similarly, the FDA recently tested a number of unapproved home HIV test kits sold on the Internet that were confiscated during a criminal investigation. None produced accurate results. In reality, the outcome could have had grave consequences for a user in terms of mental and emotional stress, access to proper medical treatment, and transmission of the disease to others. The FDA's Center for Biologics Evaluation and Research, which reviews all blood-related products, continues to investigate firms and people involved in the illegal sale of unapproved HIV home test kits in the United States.

Follow the Directions
Home test kits, for the most part, involve relatively simple procedures. Some are as straightforward as one pregnancy test in which chemically treated test strips dipped in urine produce colored indicator lines. Others require a finger prick and the placement of a blood sample onto a reagent strip. The strip is inserted into a machine that measures blood glucose levels. Still others, like the only FDA-cleared HIV home sample collection kit, consist of multiple components, ranging from pre-test counseling information to a personal identification number for obtaining the test's results. In any case, the FDA requires that the kits be simple enough for an average consumer to use at home without a doctor's supervision.

Some home tests give their results as positive or negative. Performance of these is described in terms of sensitivity--the probability that the results will be positive when a disease or condition is present; and specificity--the probability that the results will be negative when a disease or condition is not present. Other home tests give numerical results. Performance of these is described in terms of precision--how reproducible the results are when a test is run over and over; and accuracy--how well the results compare to a laboratory test. All diagnostic tests have limitations, and sometimes their use may produce erroneous or questionable results. Test results obtained at home can often be clarified by a physician, who may recommend another test that is handled by a laboratory.

Gutman, whose office is within CDRH, says that home test kits should not be stored in places where they might be exposed to extreme temperatures, since this may cause product deterioration over time. He also stresses the importance of checking test-kit expiration dates--chemicals in an outdated test may no longer work properly, so the results are not likely to be valid.

While manufacturers of professional test kits used in clinics and hospitals or doctor's offices are required to include sensitivity and specificity information in their labeling, the FDA does not make manufacturers of home test kits do so. But Lori Moore of Maysville, Ky., thinks they should.

"As a consumer, I want to see the data that supports this being a good brand," she says. "For the average person, this information truly lets them know what they're purchasing." But Moore happens to be more familiar with sensitivity and related product information than most people, since she has worked as a registered laboratory technician. Still, she insists that today's consumer wants more information visible on the product's label than is currently available.

Dave Lyle, a medical technologist in the FDA's clinical laboratory devices division, explains that "the decision was made several years ago to exclude this information from over-the-counter kits because it might confuse the consumer." However, Lyle agrees that "in today's world, most consumers are very sophisticated and want as much information as possible to make an informed decision."

Complications of home testing may interfere with obtaining accurate results. Consumers may not be able to follow the instructions. Proper collection, storage and shipment of specimens are all critical for accuracy. Samples held too long, for example, or subjected to severe temperature changes could generate false positive or negative readings. Urine samples taken too early or too late in the day or foods eaten that mimic the metabolites being measured also can produce inaccurate readings.

And people need to beware of bogus tests--those not cleared by the FDA. Unapproved home test kits do not come with any guarantee of accuracy or sensitivity, nor do they have a documented history of dependability. Proper training to interpret results is not provided with the kits, and they do not have a validated record of precision. This means that unapproved tests may be inconsistent and inaccurate.

Approved tests, on the other hand, have undergone extensive study and review by the manufacturer of the product to satisfy the FDA's requirement that they are as safe and accurate for consumer use as their laboratory counterparts are for professional use. For any in-home test, the manufacturer must convince the FDA that the results of a test will benefit consumers and that consumers have the knowledge necessary to decide whether testing themselves is appropriate.

For example, Stewart says people purchasing blood pressure monitors should look for a statement in the label that says the device has been validated in a human study "where the statistics have been calculated to ensure that good accuracy can be demonstrated." Stewart says the label also should include a statement that says measurements obtained by the blood pressure monitor are equivalent to those obtained by a trained observer using a cuff and stethoscope.

"Indeed, reading the label is the most important thing," he says, "but it might also be useful to ask the pharmacist or one's doctor to get a recommendation."

Popular But Not Perfect
Amid sweeping changes in U.S. health care, the trend toward cost-effective self-care products used in the home emphasizes prevention and early intervention. The home test kit market is offering faster and easier products that lend themselves to being used in less-sophisticated environments to meet consumers' needs.

However, Gutman emphasizes, "even the best screening tests are occasionally wrong. No tests, whether performed at the lab or in the home, are perfect."