Assessing the nicotine content in toenail clippings may help predict a woman's risk of developing heart disease, says a new study.
The US study on nurses suggests that measuring the nicotine content in toenail clippings can help in calculating the risk.
The researchers analysed the toenails of more than 62,500 women, who showed double the level of nicotine in those with heart disease than those without the condition.
The team believes that the test can bring out more accurate results than simply asking a person about their smoking history.
It is well established that smokers have a higher risk of heart disease.
There are existing tests for the presence of nicotine in the body, for example testing the amount of nicotine breakdown products in saliva or urine, but they only reflect recent exposure to cigarette smoke.
Lead researcher Dr Wael Al-Delaimy from University of California, San Diego said because toenails grow slowly - at a rate of around 1cm a year - they may offer a longer-term estimate of a person's total exposure to tobacco smoke, whether active or passive.
"The use of toenail nicotine is a novel way to objectively measure exposure to tobacco smoke and could become a useful test to identify high-risk individuals in the future," BBC quoted him, as saying.
During the study 900 women were diagnosed with heart disease. The women in the top fifth for toenail nicotine content were thinner, less active, heavier drinkers, and more likely to have high blood pressure or diabetes, as well as a family history of heart attack, compared to those with less nicotine in their toenails.
Ellen Mason, a cardiac nurse at the British Heart Foundation (BHF) said the study emphasised that smokers are storing up health problems for the future.
"Men and women who smoke are around twice as likely to suffer a heart attack in their life time as those who don't, and quitting smoking is one of the most effective ways to reduce this risk," she said.