neonatal screening in Kuwait how to decrease false postive

1. By
Dr.Amir Abdelazim Ahmed

2. Introduction:
• Newborn screening is not the same as diagnostic testing.
• A diagnostic test can tell with more certainty whether or not a child
has a genetic condition.
• On the other hand, a screening test simply indicates that a child may
have a condition.
The purpose of a screening test is to catch all babies that may have a
condition. This means that many children with an out-of-range
screening result are healthy. When a child with an out-of-range
newborn screening result has a follow-up test result within the
normal range, it is sometimes called a “false positive”.

3. •DELFIA
•TANDEM MASS
SPECTROMETRY

4. Wilson and Jungner
Principles and practice of screening for disease WHO 1968
• An important health problem
• Accepted treatment
• Facilities for diagnosis and treatment
• Recognizable latent or early symptomatic stage
• Suitable test or examination
• Test acceptable to the population
• Natural history understood
• Agreed policy on who to treat
• Costs economically balanced
• Case finding a continuous process

5. Expanding of Kuwait national program in Oct2014
Why more diseases?
• More treatment available
• Early detection: less health damage
• More tests available (high throughput)
• MS/MS

7. Decreased credibility
result from false positive results

8. Impact of false positive results
• Anxiety
• Increased costs to parents
• Increased costs to society
• Decreased credibility for NBS program
• Potential for missing appropriate follow-up of a real patient
• Missing a diagnosis of a potentially treatable metabolic condition,
resulting in Morbidity and mortality associated with the condition

9. First test positive, more tests needed…

11. MOTHER
TANSPORTATION
LAB ANALYSIS
BABY
COLLECTION
RESULT INTERPRETATION
WHY DID THIS HAPPEN?
EG:
MATERNAL PKU
MATERNAL TREATED FROM HYPERTHYROID
MATERNAL WITH CAHEG:
PREMATURE
LOW BIRTH WT
SICK
SPECIAL FEEDING
EG:
BAD QUALITY
BAD QUANTITY
TIME OF COLLECTION
EG:
HEAT AND HUMIDITY
EG:
IMPROPER PIPITING
INCORRECT STEPS TIMING
EG:
CUTOFF UNSUITABLE

14. • Exogenous pivalate administration had been previously identified as
the causal agent of this concern. No pivalic-ester prodrug is
commercially available in Belgium, but pivalic derivates are also used
in the cosmetic industry as emollient under the term
“neopentanoate”. We have identified neopentanoate-esters in a
nipple-fissure unguent that was provided to young mothers. Ceasing
distribution of this product hugely reduced the C5-carnitine false
positivity rate.

15. We have lab challenge

16. RESULT INTERPRETATION

17. To understand we will discuss
• Screening tests
• Optimising screening cutoffs
• Second tier testing

18. Screening tests
“The presumptive identification of unrecognized disease or defect by
the application of tests, examinations, or other procedures which can
be applied rapidly” Oxford dictionary
• Screening tests are not intended to be diagnostic.
• Screening tests sort out apparently well persons who probably do not
have the disorder from those who probably do.
• Persons with a positive or suspicious finding must be referred for
diagnostic testing. “”confirmatory tests “”

19. number of positive or negative depending on
cutoff
Setting action limits--‐
Accepted compromise

21. How to decrease false positive

27. 2nd tier test
• 2nd specific test on same sample used for primary screen
• Different target analytes –different methodology used
• Can use more moderate primary cut off (in house false positive)
• Usually slower (turn around time )
• Often uses column separation (separates isomers)
• A cost effective approach to implement clinically
• defined cutoffs when normal population and disease range overlap (poor specificity).
• After primary screening test.
• Same specimen = no additional patient contact!
• Normal result overrules primary screening result!
• Can be regionalized.

28. 2nd tier

29. Test discrimination
Primary screen test
Disorder possible
Second tier test
Further testing on the original sample
to provide better discrimination
Disorder likely
Diagnostic tests
Disorder proven

30. What is the purpose of second tier tests?
• Identify infants at risk of having a metabolic condition, while
• Reducing false positives (proportion of non-affected individuals who test
positive), and
• Reducing false negatives (proportion of true affected individuals who test
negative)

31. • Steroid profile for CAH
• Total homocysteine (elevated/low methionine)
• Glutarylcarnitine (elevated C5DC-carnitine)
• Methylmalonic/methylcitric acid (elevated C3)
• Allo-isoleucine (elevated Xle)
• Ethylmalonic acid (elevated C4-carnitine)
• Guanidinoacetate for GAMT deficiency

32. 2nd tier test for elevated C3-carnitine
• Specific markers for metabolic conditions: Elevated C3-carnitine
Methylmalonic/methylcitric acid
year marker condition postive confirmed Ppv%
2006 C3 PA.MMA 202 1 0.5
2013 C3 PA,MMA 11 11 100
ATLANTA

33. Steroid profile
• Primary screen (immunoassay)
• 2nd tier
- Can not test all babies using
same tandem due to run time

34. 2nd tier DNA
• Used for many disorders
• Moving toward diagnostic
• Use NGS

36. Disorder Marker First screen confirmed PPV%
1 Biotindase Biot.enz 81 61 75.31%
2 VLCAD C14:1 38 6 15.79%
3 IVA C5 28 0 0.00%
4 CAH 17OHP 232 7 3.02%
5 MMA/PA C3 118 5 4.24%
6 MCAD C8 57 0 0.00%
7 LCHAD/TFP C16OH 16 0 0.00%
8 3HMG/MCC/MCD/BKT C5OH 14 3 21.43%
9 GALACTOSEMIA T.GAL + GALT 15 4 26.67%
10 CONGENITAL HYPOTHYRODISM TSH 110 44 40.00%
11 MSUD LEU/IISe 70 0 0.00%
12 HOMOCYSTINURIA/HYPERMETHIONEMIA Met 119 2 1.68%
13 PKU/HYPERPHENYLALANEMIA Phe 49 6 12.24%
14
TYROSINEMIA
TYR+ 2nd tier succinylacetone
16 1
6.25%
15 CITRULINEMIA/ASA Cit 33 2 6.06%
16 GLUTRIC ACIDURIA C5DC 14 3 21.43%