By ANDREW POLLACK
Want to know how long you will live?
Blood tests that seek to tell people their biological age — possibly offering a clue to their longevity or how healthy they will remain — are now going on sale.
But contrary to various recent media reports, the tests cannot specify how many months or years someone can expect to live. Some experts say the tests will not provide any useful information.
The tests measure telomeres, which are structures on the tips of chromosomes that shorten as people age. Various studies have shown that people with shorter telomeres in their white blood cells are more likely to develop illnesses like cancer, heart disease and Alzheimer’s disease, or even to die earlier. Studies in mice have suggested that extending telomeres lengthens lives.
Seizing on that, laboratories are beginning to offer tests of telomere length, setting off a new debate over what genetic tests should be offered to the public and what would be the ethical implications if the results were used by employers or others.
Some of the laboratories offering the tests emphasize that the results are merely intended to raise a warning flag.
“We see it as a kind of wake-up call for the patient and the clinician to say, ‘You know, you’re on a rapidly aging path,’ ” said Otto Schaefer, vice president for sales and marketing at SpectraCell Laboratories in Houston, which offers a test for $290.
A company in Spain, provocatively named Life Length, has begun selling a test for 500 euros ($712), that says that it can tell people their biological age, which may not correspond to their chronologic age.
Another company, Telome Health of Menlo Park, Calif., plans to begin offering a test later this year for about $200. It was co-founded by Elizabeth H. Blackburn of the University of California, San Francisco, who shared a Nobel Prize in 2009 for discoveries related to telomeres.
Calvin B. Harley, the chief scientific officer at Telome Health, said the test would be akin to a car’s dashboard signal, a “check engine light.” He compared it with a cholesterol test, but more versatile since it can predict a risk of various illnesses, not just heart attacks.
But among the critics of such tests is Carol Greider, a molecular biologist at Johns Hopkins University, who was a co-winner of the Nobel Prize with Dr. Blackburn.
Dr. Greider acknowledged that solid evidence showed that the 1 percent of people with the shortest telomeres were at an increased risk of certain diseases, particularly bone marrow failure and pulmonary fibrosis, a fatal scarring of the lungs. But outside of that 1 percent, she said, “The science really isn’t there to tell us what the consequences are of your telomere length.”
Dr. Greider said that there was great variability in telomere length. “A given telomere length can be from a 20-year-old or a 70-year-old,” she said. “You could send me a DNA sample and I couldn’t tell you how old that person is.”
Dr. Peter Lansdorp, a telomere expert at the British Columbia Cancer Agency, also had doubts. “If telomeres are short for you or me, what does it mean?” he said. Dr. Lansdorp started a company, Repeat Diagnostics, which conducts telomere testing for medical researchers only.
Recent media reports speculated on the tests and their possible implications, including ethical problems.
“You could imagine insurance companies wanting this knowledge to set rates or deny coverage,” said Jerry W. Shay, a professor of cell biology at the University of Texas Southwestern Medical Center in Dallas, who is an adviser to Life Length.
Test vendors say the speculation is running wild.
“It doesn’t mean we will tell anyone how long they will live,” said María Blasco, a co-founder of Life Length and a molecular biologist at the Spanish National Cancer Research Center in Madrid. Even if a 50-year-old has the telomere length more typical of a 70-year-old, she said, “This doesn’t mean your whole body is like a 70-year-old person’s body.”
Still, she said, “We think it can be helpful to people who are especially keen on knowing how healthy they are.”
Generally tests offered by a single laboratory do not have to be approved by the Food and Drug Administration. But the F.D.A. has been cracking down recently on some tests offered to the public, saying they may need approval. The FDA said in a statement Wednesday that it was aware of the tests, and had not come to any conclusions.
Executives at both Telome Health and Life Length say they will require a doctor to be involved in ordering the test, though SpectraCell said it allowed individuals to order the test.
Telomeres are stretches of DNA linked to certain proteins that are at the ends of chromosomes. They are often likened to the caps at the end of shoelaces. Each time a cell divides, the telomeres get shorter. Eventually, the telomeres get so short that the cell can no longer divide. It enters a state of senescence or dies.
One study in Utah, using blood samples from 143 elderly people collected in the 1980s, found that those with shorter telomeres were almost twice as likely to die in the ensuing years as those with longer ones.
Another study, published in The Journal of the American Medical Association last July, followed 787 people in Italy, all initially free of cancer. Those with the shortest telomeres had three times the risk of developing cancers in the next 10 years as those with the longest telomeres.
Still, not all studies have found such strong correlations. In any case, correlations do not prove that the shorter telomeres are causing the problems, although experts say some animal and cell studies do suggest causality.
Some say that the telomere test might not tell people much that cannot be learned in other ways.
“You can pretty much look at people and determine their biological age,” said Michael West, who founded Geron, the biotechnology company that sponsored and conducted some important research on telomeres. He now runs BioTime, another biotechnology company.
It is also unclear what to do about short telomeres. At the moment, there is no drug that can lengthen telomeres, though researchers are working on drugs and stem cell therapies.
There is some evidence, however, that stress is associated with shorter telomeres and that stress relief, exercise or certain nutrients such as omega-3 fatty acids might at least slow the decline in telomere length. But healthy lifestyles are already recommended for people without having to know their telomere length.
There are also disputes about how to measure telomeres. Life Length says its technique, while more expensive, can detect not only average telomere length but the shortest telomeres in cells. The shortest telomeres cause the health problems, said Dr. Shay, the adviser to Life Length.
Telome Health and SpectraCell use a DNA amplification technique called polymerase chain reaction, or P.C.R., which is cheaper but provides only an average length. And there are some questions about the accuracy.
Dr. Harley of Telome said the P.C.R. test was more relevant because virtually all the studies correlating telomere length with disease had used that test.
For those wanting to know how long they might live, there are already some indexes that are used by geriatricians to estimate the chances of a patient dying in anywhere from six months to nine years. A patient with a short expected lifespan, for instance, might no longer need to undergo annual screening for cancer.
These estimates rely on factors such as person’s age, gender, smoking history, whether they have certain diseases and whether they can perform certain functions, like walking several blocks, pushing an armchair or managing their finances.
Dr. Sei Lee, an assistant professor at the University of California, San Francisco who developed a test that estimates the probability of dying within four years, said he was not sure how much telomere length testing would add. “The chance of any single factor being a great predictor is probably low,” he said.