Home testing kits can check for high cholesterol, but not Lp(a) specifically
Scientists say they have found proof that another "bad" type of cholesterol contributes to heart disease.
Unlike the well-known LDL cholesterol, lipoprotein(a) or Lp(a) cannot be controlled by cutting down on dietary fats or taking a statin drug.
But researchers say high levels do not carry the same risk as LDL.
And other drugs might work to minimise its effects, they told the New England Journal of Medicine.
LDL is considered the aggressive tiger of the cholesterol world, furring the arteries and greatly increasing heart risk. Scientist believe Lp(a), which is inherited, is more of a pussycat, although it does appear to upset blood clotting.
The researchers used gene-chip technology to scan DNA that they knew from previous studies were potential "hotspots" for heart disease risk. This analysis revealed the two genetic culprits.
Professor Martin Farrall, lead author of the study carried out at Oxford University, said one in six people carries one or more of the genes for Lp(a).
He said: "The increase in risk to people from high Lp(a) levels is significantly less severe than the risk from high LDL cholesterol levels.
"So Lp(a) doesn't trump LDL, which has a larger impact and which we can already control pretty effectively.
"The hope now is that by targeting both we could get even better risk reduction."
Some existing drugs, such as Niacin, and others coming on to the market, such as CETP-inhibitors, lower Lp(a) as well as LDL cholesterol.
Professor Peter Weissberg of the British Heart Foundation, which funded the study, said the findings were useful but urged people not to be alarmed by them.
"They highlight the importance of trying to lower Lp(a), which will spark new efforts to design a medicine to achieve this effectively.
"And they reveal clues that open a new avenue for research to decipher how heart disease develops.
"But LDL is still the type of cholesterol to be more concerned about."
Fats from food are turned into cholesterol by the liver. There are different types but some, such as LDL, are known as "bad" cholesterol. They can lead to a build-up in the body's cells.
Prof Weissberg said everyone could reduce their risk of heart disease by eating a healthy balanced diet, being physically active and avoiding smoking.