Biochemistry Flashcards
Where does biochemistry fit in making a diagnosis
Used at the end of a clerking after differential diagnosis has been made to tease out different explanations
Marker for myocardial infarction
Troponin
Marker for muscle breakdown
Creatine kinase
Terms used in biochemistry to describe how good a test is
Accurate - How close result is to the true value
Precise - How predictable test result is
False positive vs false negative
False positive is a healthy person whose result lies in disease territory whereas false negative is a disease person who lies in healthy category
Sensitivity of a test
% of disease people who have a positive test
Specificity of a test
% of healthy people who have a negative test
Pitfall of sensitivity and specificity
You have to know who has or doesn’t have the disease which isn’t always possible.
Positive predictive value
% of positive tests in disease people; post-test probability of disease
Negative predictive value
% of negative tests in healthy people; post-test probability of health
Prevalence
% of total people tested who have disease; pre-test probability of disease
How does prevalence affect positive predictive and negative predictive valule
As prevalence falls, positive predictive value falls
As prevalence falls, negative predictive value rises
How does prevalence affect sensitivity and specificity
Stays the same
