Biochemistry tests and what they mean Flashcards
What are clinical biochemistry tests used for?
Various different purposes, diagnosis, guiding treatments, prognosis and screening
What is accuracy?
How close the result is to the true value
What is precision?
A different concept that requires repeated measurement of something, - it gives you an idea of how predictable your test result will be
E.g Precise - gives the more of less same result each time, even if its not on target
What is a false positive?
A healthy person who’s result is the ‘disease’ territory and which therefore acts as a false alarm (abnormal test result, disease absent)
False positive: the patient does not have the disease but the test is positive
What is a false negative?
A person with the disease whose result is in the healthy territory and which is therefore false reassuring (normal test result, disease present)
False negative: the patient has the disease but the test is negative.
What can you measure as a marker of muscle damage?
CK creatine kinase
What is a true positive?
A result in which the test is abnormal in a person with a disease (person has the disease)
True positive: the patient has the disease and the test is positive.
What is a true negative?
Where the test is normal in a person who does not have the disease (person doesnt have the disease)
True negative: the patient does not have the disease and the test is negative
What is sensitivity?
The sensitivity of a clinical test refers to the ability of the test to correctly identify those patients with the disease.
Sensitivity = true positives/(true positives + false negatives)
(need to know who does and who doesnt have the disease to know this info)
What is specificity?
The specificity of a clinical test refers to the ability of the test to correctly identify those patients without the disease.
Specificity = true negatives / (true negatives + false positives)
(need to know who does and who doesnt have the disease to know this info)
What is the positive predictive value?
‘How likely is it that this patient has the disease given that the test result is positive?’
The likelihood of a disease in a person with a positive test.
(you dont need to know who and who doesnt have the disease)
What is negative predictive value?
‘How likely is it that this patient does not have the disease given that the test result is negative?’
Likelihood of health in someone with a negative (normal) test result. ??
(you dont need to know who and who doesnt have the disease)
What is prevalence?
Prevalence is a statistical concept referring to the number of cases of a disease that are present in a particular population at a given time
What is incidence?
incidence refers to the number of new cases that develop in a given period of time.
Describe how prevalence affects PPV and NPV?
As prevalence falls - PPV falls
As prevalence falls - NPV rises
