Diagnostic Tests

Table of Contents

1. Understanding diagnostic tests
   1. What is a 2 x 2 (read two by two) table, and what is it used for?
   2. Implications in clinical practice
   3. Likelihood ratios
   4. Using likelihood ratios
   5. Conclusion
2. Measures of diagnostic tests
3. Diagnosis

Using likelihood ratios

Going back to our patients, Fred, Jean and Kylie

Some clinical features have been found to make it more likely that the patient with acute chest pain has had a myocardial infarction. One their own they do not tell you much, but when you link them together i.e. the more of these clinical features the patient has, then the more likely it is that the patient has had a myocardial infarction, then they can help you be more certain of your diagnosis.

Equally, there are some clinical features that make it less likely the patient with acute chest pain has had a myocardial infarction.

In fact Fred had an ECG that revealed 2-mm ST-segment elevation in leads V1 to V4, Jean's ECG revealed 3-mm ST-segment elevation in leads II, III, and aVF and 1-mm ST-segment depression in I and aVL, and Kylie had a normal ECG.