Describe sensitivity
Ability of test to detect a TRUE positive
Define specificity
Ability of a test to detect a true NEGATIVE
What are important interferences with common lab tests?
Hemolysis
Lipemia (excess lipids in sample)
Icteric (high [bilirubin])
What effect can barbiturates have on lab tests?
Decrease bilirubin
What effect can any drug with liver toxicity have on lab tests?
Increase bilirubin
What effect can opiates have on lab tests?
Increase amylase
Define the reference range
Mean +/- 2 SD
How do you calculate sensitivity ?
What does it mean
Ability to detect a true positive in a person afflicted with the disease
Sensitivity = TP/ (TP + FN)
How do you calculate specificity?
What does it mean?
Ability to exclude a diagnosis in a healthy person
Specificity = TN / (TN + FP)
Sensitivity refers only to the _______ population
Specificity refers only to the ______ population
Sensitivity = diseased
Specificity = healthy
Describe how changes in disease prevalence affect predictive values of tests
Inc. prevalence
= predictive value of (+) test improves
Dec. prevalence
= predictive value of (-) test improves
= predictive value of positive test in diminished
How do you know if the therapy has changed the patient’s lab values?
To determine if there’s a difference between first and subsequent measurements,
Difference between two measurements must be >3x the SD of the assay
= 95% confident difference between measurements is not due to chance!
