Patients who go to Brigham and Women’s Hospital for routine care will soon be asked to provide a blood sample for genetic testing, with the results used to build a massive database to help untangle how genes affect human health.

The researchers ultimately hope to compile genetic information from 100,000 patients — some ill, some healthy. By linking the data to medical records and following patients over time, the scientists hope to illuminate the interplay of genes, lifestyle, and the environment in causing disease.

Participation will be voluntary, and patients will not have access to results. The information will be used entirely for research.

The new effort at the Brigham is part of a much broader international trend, in which researchers are asking volunteers to become part of such large databases.

Also in Boston, Children’s Hospital’s Gene Partnership Project has signed up close to 500 participants since last fall, and eventually it hopes to enlist 10,000 to 20,000 patients a year.

Further afield, health care provider Kaiser Permanente is building a large database of participating members, the UK Biobank has recruited more than a half-million people, and at Children’s Hospital of Philadelphia, researchers are more than halfway toward their goal of building a genetic database of 100,000 children.

“Researchers, clinicians, and patients are aware of the critical role that genes, as well as environment, as well as lifestyle, play in terms of human health and human disease,’’ said Dr. Christine Seidman, a cardiologist who is a leader of the new OurGenes, OurHealth, OurCommunity program at the Brigham.

“The opportunity to understand those has been limited to selected investigations of a particular disease — cancer, diabetes, or the like — yet we know that individuals, patients in the hospital, don’t have just one thing . . . and we’d also like to understand the crosstalk between those different conditions,’’ such as how diabetes affects kidney disease and heart disease, she said.

What sets such efforts apart from previous genetic studies is not only their size, but also the way in which they are designed to integrate genetic information with the medical record, family history, and a detailed health questionnaire. In addition, the patients’ health will be tracked over many years.

“Many of us feel that within 10 years, it’ll be routine to sequence a human genome — at less than the current cost of the colonoscopy,’’ said David Hunter, a professor of cancer prevention at the Harvard School of Public Health, who is not involved in either of the Boston studies. “The problem is converting all those sequences into actionable clinical information will require very, very large studies. These are the first generation of such studies.’’

In the decade since the first human genome was decoded, important progress has been made in understanding the genome, and technology has been developed at breathtaking speeds. But even as studies have made progress in finding genetic variations that contribute to disease, they haven’t yet yielded much information useful for guiding treatment.

The Brigham study will start later this month with a pilot phase that will recruit 600 patients through six clinics. Patients will receive a letter at home about two weeks before an appointment, alerting them to the possibility of participating. Their data will not be given to health insurers, nor will it be put in patients’ medical records. Patients will not be charged for the testing, with the $250,000 cost covered by internal hospital funds. Researchers will need to raise further funds to pay for the full project.

The genetic information collected will not affect patients’ medical care unless researchers find something with profound and immediate medical implications. An example, Seidman said, of such a condition is a mutation known to cause sudden cardiac death.

“The way I would look at it is sort of like the Census — you want your information to be recognized and be part of any solution that’s found to any health issue. And if your genetic material is not there, it can’t be counted,’’ said Dr. Elinor Mody, medical director of the Fish Center for Women’s Health, one of the Brigham pilot sites.

The Children’s Hospital Boston project, on the other hand, is taking the unusual step of informing families about what researchers find in their genes.

Ultimately, the study offers benefits to both doctors and patients. Patients’ data will contribute to new genetic research, and patients themselves will potentially benefit from findings about risk or potential therapies that are relevant to their genetic makeup, said one of the leaders of the Children’s initiative.

“Every single patient we encounter should be an opportunity to learn, and these are the first important steps,’’ said Dr. Isaac Kohane, one of the principal investigators of the Gene Partnership Project.

Carolyn Y. Johnson can be reached at cjohnson@globe.com.

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