If you could find out exactly how long you have left to live, would you want to know?

A blood test could show you just that - and it is terrifyingly accurate.

Telomeres are located at the end of chromosomes. Each time that a cell replicates itself, the telomeres became shorter and shorter until they snap off. The length of telomeres should indicate how long you have left to live if you were to die of natural causes.

Telomeres have long been believed to be linked to the age of death and can be thought of as internal clocks. Tests are even on the market right now; a test in the United Kingdom can be bought for £400, or about $640.

However, many doctors had been wary of the tests, saying that the science behind them was still in its infancy. Previously, the test had only been administered on experimental animals in laboratories. A recent study published in the journal Molecular Ecology, on the other hand, performed the tests on wild animals for the first time.

The test was performed on a population of 320 Seychelles Warblers living on the Cousin Island. The birds were studied for 20 years. Because the birds are on a remote island, there are no natural predators and not a lot of migration, so researchers could accurately find a link between an individual bird and the average life expectancy rate.

"We saw that telomere length is a better indicator of life expectancy than chronological age. So by measuring telomere length we have a way of estimating the biological age of an individual - how much of its life it has used up," David Richardson, one of the study authors, said to The Independent.

Researchers had previously thought that telomeres shorten uniformly across a population. However, this study found that some people have longer telomeres than others. Individuals with longer telomeres will live longer natural lives than people with shorter telomeres.

"However while telomeres do shorten with chronological age, the rate at which this happens differs between individuals of the same age. This is because individuals experience different amounts of biological stress due to the challenges and exertions they face in life. Telomere length can be used as a measure of the amount of damage an individual has accumulated over its life," Richardson said.