Heart Education Awareness Resource and Training through eLearning (HEARTe)



Sensitivity & Specificity of Tests

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How accurate is the test?
Appreciation of the value of tests requires an understanding of the sensitivity and specificity of the test as well as the pre-test probability of disease. No test result is 100% accurate in every case, every time. Very few are sensitive enough to accurately detect disease in every case nor specific enough to accurately rule out those who don’t have the disease. A reliable test has a high level of both sensitivity and specificity.

Sensitivity is the fraction of all those with the disease who correctly get a positive (abnormal) test result, for example, ETT has 67 % sensitivity1 so for 67 in 100 with Angina, it can be expected to give a true positive result. Compare this to the sensitivity of CT coronary angiography2 which is 89%.

Specificity is the fraction of those without the disease who correctly get a negative (normal) test result, for example, an ETT has 72 % specificity1 so for 72 in 100 without Angina, it will give a true negative result. Compare this to the specificity of CT coronary angiography2 which is 96%.

Pre-test probability is also important. This means considering how likely the person is to have underlying coronary heart disease and this will be dependent on their risk factor profile as well as the prevalence of the disease in that particular population.

A young woman about 35 years old, who has never smoked, has a normal cholesterol and no diabetes has a low probability3 of coronary heart disease. If she presents with chest pain which sounds non-cardiac, she only has a 3% probability of CHD. If you give her an ETT “just to make sure” it is not cardiac, you may get a false positive result.

Whereas,if you do an ETT on a 65 year old man with atypical angina, who smokes, has a raised cholesterol and type 2 diabetes and therefore a high probability3 of CHD of 86%, the ETT result will be much more reliable. The ETT is more sensitive in the moderate-high probability group.

Pulse point

It is important to consider that sometimes, for example, with an ETT, the result will be more reliable/meaningful if we ensure that the individual does not have a physical condition, such as peripheral arterial disease (PAD) or arthritis as these may limit how many minutes they can exercise for.

Page last reviewed: 30 Jul 2020