With Congress poised to eliminate a big barrier to genetic testing for risk of certain diseases, consumers still face challenges in figuring out which ones offer useful information.

Despite heavy marketing by some genetic-test makers, the wide use of genetic tests has been held back by a variety of factors, including questions about the tests' usefulness and concerns that results could be used by employers and insurers to discriminate against people. Critics argue that many tests can't accurately identify which people are at risk for various illnesses.

But genetic researchers say that certain genetic tests are valuable because they do tie closely to particular medical conditions and patients can help their health by acting on the tests' findings.

Among tests that have broad support among doctors are a breast- and ovarian-cancer test that looks at genes known as BRCA1 and BRCA2, and a colon-cancer test that examines three genes linked to a form of the disease known as hereditary nonpolyposis colorectal cancer, or HNPCC. The tests are generally given only to patients who, due to family history and other factors, appear likely to carry the problematic genes.

Kenneth Offit, chief of the clinical genetics service at Memorial Sloan-Kettering Cancer Center in New York, says that when these tests signal a genetic risk, patients can take action. In the case of the breast-cancer test, for instance, he recommends that patients get yearly magnetic resonance imaging scans starting at the age of 25, rather than relying on typical mammograms that often start in the mid-30s. If the colon-cancer test results show a danger, he urges patients to begin annual colonoscopies at 25, rather than the typical practice of having a first one at 50.

Gene tests associated with a number of relatively rare diseases have also won general acceptance. One detects a condition called factor V Leiden, which is associated with an elevated risk of blood clots. Brian F. Gage, an associate professor at Washington University in St. Louis, suggests the test for women with a strong family history of clotting problems who are considering taking birth-control pills, which also carry a clotting danger. If a woman does have the risky genetic variant, he would urge her to consider different contraception.

New congressional action is expected to boost the tests' appeal. The House was expected as soon as Thursday to pass a bill that will bar employers and insurers from discriminating based on genetic makeup. The long-stalled legislation won a unanimous Senate vote and is expected to get President Bush's signature. The insurance provisions are set to take effect a year after the bill is signed, while those dealing with employers kick in after 18 months.

But newly interested consumers will find a confusing landscape, with an array of companies marketing more than 1,400 different genetic tests, sometimes with little evidence. Unlike new drugs, lab tests typically aren't reviewed by federal regulators before they go on the market. In a draft report last year, a federal advisory committee called for more oversight of genetic testing; a final version is supposed to come out Thursday.

Many new genetic tests — even those based on well-regarded research — have so far won only limited support from medical groups. Genetic researchers say this is often because the genes don't account for a large portion of the disease risk, or the tests' results don't clearly justify changes in patients' behavior.

Major insurers such as Aetna Inc., WellPoint Inc. and Cigna Corp. say they're generally not paying for broad genome reviews or tests that they believe fall into the unproven category, such as ones that are supposed to signal a predisposition toward Type 2 diabetes, early heart attacks or prostate cancer.

Very-well-established genetic checks, such as the BRCA test, do tend to be covered for patients who meet certain criteria. The federal Medicare program, which isn't mandated to include screening technologies, doesn't typically pay for genetic tests meant to detect disease risks.

Tests are often pricey, costing hundreds of dollars. "In the common diseases, there's more predictive information today in knowing family members had it than knowing" the results of the newly developed genetic tests for such conditions as Type 2 diabetes, says David Altshuler, a professor at Harvard Medical School.

For instance, it isn't clear how much patients can learn from current genetic tests designed to signal heart-attack risk, beyond standard measures such as blood pressure that are already checked by doctors, says Teri Manolio, director of the office of population genomics at the National Human Genome Research Institute. "It's just way too early," she says.

On the other side, Jianfeng Xu, a professor at Wake Forest University who helped to research a prostate-cancer test highlighted this year in a study published in the New England Journal of Medicine, says he believes that the test can be useful for patients with a family history of prostate cancer. It will be more powerful, though, when scientists can distinguish whether the risk is for more-aggressive form of the disease, says Dr. Xu, who has co-founded a company that will market the test.

Kari Stefansson, chief executive of deCODE genetics Inc., an Icelandic company that markets an array of genetic tests as well as a broad genetic scanning service, says tests for such conditions as Type 2 diabetes are important, partly because negative results may convince consumers to try healthier behaviors. "All preventative medicine is based on the assumption that you can raise concerns," he says. "Are these guys telling me it hasn't been worth measuring cholesterol all these years because other factors also affect heart disease?"

Some researchers say they are also skeptical of the health value of services that broadly scan patients' genetic patterns.

"You get a lot of information, but very little knowledge," says Howard McLeod, a professor at the University of North Carolina. Anne Wojcicki, co-founder of 23andMe Inc., a company that markets genetic information to consumers, says she agrees that "it's still the early stages of what the clinical utility is," but some consumers are interested in their genetic makeup.