Biochemistry tests Flashcards
What are tests used for?
Monitoring, diagnosis, screening, prognosis, treatment
What is accuracy?
How close the result is to the true value
What is precision?
How reproducable the result is
What is the reference interval?
The middle 95% of the population
What are false positives?
People who do not have the disease but test positive because they have a high level of the marker
What are false negatives?
People who DO have the disease but test negative because they have a low level of the marker
What is sensitivity and how do you calculate it?
How good a test is at identifying disease.
True positives/True positives+False negatives
What is specificity and how do you calculate it?
How good a test is a identifying the healthy population
True negatives/True negatives+False positives
What is the Positive Predictive Value and how do you calculate it?
Post test probability of disease.
True positives/True positives+False positives
What is the Negative Predictive Value and how do you calculate it?
Post test probability of health
True negatives/True negatives+False negatives
What is the prevalence and how do you calculate it?
Pre-test probability of disease (the percentage of the population with the disease)
True positives+False negatives/Total population
How does the prevalence affect the PPV, NPV, sensitivity and specificity?
If prevalence rises:
PPV increases
NPV decreases
Sensitivity and specificity remain the same
When are tests most useful?
When the prevalence is 50%. When you are 50:50 as to whether this presentation matches this disease
Where is the diagnostic cut off?
The upper end of the reference value
If someone has a negative troponin after 12 hours have they had an MI?
NO
