Screening

Question 1

Sensitivity

Answer 1

Remember SnNout- a sensitive test means a Negative helps rule the disease OUT.
sensitivity is the proportion of those who test positive when the disease is present i.e. True positive/ (true positive + false negative)

Question 2

Specificity

Answer 2

Remember SpIN- a specific test helps rule IN a positive test

Proportion of people who test negative when the disease is absent i.e. True negative/(true negative + false positive)

Question 3

PPV

Answer 3

Probability that following a positive test result, the individual truly has the specific disease i.e. True positive/(true positive + false positive)
- INCREASES as prevalence INCREASES - more false positives for every true positive (high prevalence)

Question 4

NPV

Answer 4

Probability that following a negative test result, the individual will truly not have the disease i.e. True Negatives/(true negatives + false negatives)
- INCREASES as prevalence DECREASES bc more true negatives for every false negative- false negative unlikely though as disease is rare (low prevalence)

Question 5

Screenings in first trimester

Answer 5

Booking blood test:
Syphilis 
Hepatitis B & C
Thalassaemia
Rubella
HIV
Blood Group & Rhesus

Ultrasound:
aneuploidy

Question 6

Screening in 2nd trimester

Answer 6

Pre-eclampsia

Question 7

Screening in 3rd trimester

Answer 7

Gestational diabetes (28 w)
Group B Streptococcus (28/34 w)
Macrosomia / growth restriction
Preeclampsia