Sensitivity and Specificity

From my LinkedIn Post

For the less scientific it might be worth revisiting the concepts of sensitivity and specificity. 

The ideal test should be 100% accurate, it should be specific ie never say you have a disease when you don’t (low false positives) and sensitive ie never say you don’t have a disease when you do (low false negatives)

Now very few medical tests meet this 100% goal. The classic example that people might be familiar with is the urine pregnancy test – if it says you are pregnant you almost certainly are pregnant, but if it says you aren’t, there is a chance you are so check again..

Now Covid testing is interesting as although the experts say the lab bit of the test is almost 100% there is a huge human factor involved in the test especially in self testing or through a car window. If you don’t insert the swab far enough in or get enough of a sample the false negative rate can apparently be high.

What does this mean & what is the implication? Well it means if it says you have covid – you almost certainly do.. but if it says you don’t, well you might still have it.. especially if you have classic symptoms – temp and cough.. 

So my advice is don’t rely on a negative test to assume you are safe to go back to work or see vulnerable relatives, which is what some of my patients are doing.