Emerging infectious diseases - Diagnostic response

Question 1

What are the steps in diagnostic assay development? (6)

Answer 1

1. Problem definition
2. Collection of background information about pathogen/infection
3. Defining criteria & assay requirements
4. Choosing a method
5. Validating
6. Interpretation of results

Question 2

What is important to take into account in the problem definition when developing diagnostic assays?

Answer 2

For which application the assay is going to be used

Question 3

Which to general groups of applications can assay be divided into?

Answer 3

Individual patient diagnostics vs. surveillance in larger population

Question 4

Which information about the pathogen of interest has to be gathered to be able to develop a (good) diagnostic assay? (6)

Answer 4

1. What is the pathogen
2. What are basic & structural properties of the pathogen
3. What is the clinical picture
4. What are the infection kinetics?
5. What is the epidemiology of the pathogen?
6. Are there asymptomatic cases?

Question 5

Which infection kinetics need to be known to be able to develop good diagnostics? (3)

Answer 5

1. Shedding -> when and into which bodily fluids?
2. Immune response -> when is protection & serology available?
3. Relation of infection kinetics to clinical symptoms

Question 6

What are assay requirements to take into account during diagnostic assay development? (7)

Answer 6

1. Turn-around time
2. Cost
3. Acceptability of false positives/negatives
4. Simplicity of performing the assay
5. Need for high throughput?
6. Safety requirements?
7. Possibility of cross-reaction

Question 7

Which questions need to be answered during validation of assays?

Answer 7

1. Sensitivity
2. Specificity
3. Detection limits
4. PPV/NPV

Question 8

What is important to be able to determine assay specificity/sensitivity?

Answer 8

A golden standard to compare the test against

Question 9

What happens when sensitivity is very high?

Answer 9

Higher amount of false positives -> need for extra confirmation

Question 10

What happens when specificity is very high?

Answer 10

Higher amount of false negatives -> can lead to missing cases

Question 11

When is sensitivity/specificity considered good/common/acceptable?

Answer 11

1. Good = 99%
2. Common = 95%
3. Acceptable = >90%

*note: this very much determines on the disease to be diagnosed

Question 12

Which factors are needed for correct interpretation of diagnostic assays? Who provides these factors?

Answer 12

1. Accurate specifications of the assay (manufacterer, lab)
2. Data on validation (lab)
3. Patient information (physician)
4. Optimal sampling (physician)