Intro to Lab Tests - Parsa

Question 1

What does test accuracy depends on?

Answer 1

1. Specificity
2. Sensitivity
3. Predictive value

Question 2

What is specificity?

Answer 2

• Negativity (true negatives) in the absence of disease
• If there are no false positives then test is 100% specific
• True Neg/(True Neg + False Pos)

Question 3

What is sensitivity?

Answer 3

• Positivity (true positives) in the presence of disease
• If there are no false negatives then test is 100% sensitive
• True Pos/(True Pos + False Neg)

Question 4

What is prevalence of disease?

Answer 4

• % of people with disease in a given population at a point in time
• As prevalence increases:
o True positives increase relative to false positives
o Predictive value of a positive test goes up
o Predictive value of a negative test goes down
• No effect on sensitivity and specificity of the test

Question 5

How do you establish referent (cut-off) values?

Answer 5

The best cut-off (referent) value is one with highest sensitivity (highest true positive rate) and highest specificity (lowest false positive rate)

Question 6

Parallel approach to multiple testing

Answer 6

• Low specificity

* If disease is considered present when any single test intended for the disease is positive

Question 7

Series approach to multiple testing

Answer 7

• High specificity

* If disease is considered present only when all the tests intended for the disease are positive

Question 8

What is an organ profile?

Answer 8

• Biochemical findings expected in organ damage
• AST and ALT as liver function tests
• BUN and creatinine as renal function tests

Question 9

What are Diagnostic Related Groups (DRGs)?

Answer 9

• Classify hospital patients into one of approximately 500 diagnostic groups
• DRG payment to hospital is based on diagnosis

Question 10

What is a disease profile?

Answer 10

• Abnormal biochemical findings expected to be found in a particular disease
• Ex: high cholesterol level in hypothyroidism

Question 11

Who are screening tests used on?

Answer 11

Asymptomatic population

Question 12

When would you use a diagnostic test?

Answer 12

When you suspect someone of having a certain disease

Question 13

What is predictive value?

Answer 13

• The predictive value of a positive result is the probability that the disease is present when the test is positive
• The predictive value of a negative test is the probability that the disease is absent when the test is negative

Question 14

What are the different types of testing that typical hospital lab does?

Answer 14

1. Blood chemistry
2. Hematology
3. Blood bank (immunohematology)
4. Microbiology
5. Urinalysis, serology, etc.