Newborn Screening

Bill Lefkowitz

December-ish 2001

The Exciting, Emotional and often The Exciting, Emotional and often Misunderstood World ofMisunderstood World of

PKU (Phenylketonuria)

Disorder of phenylalanine hydroxylation leading to accumulation of this amino acid. Patients with undiagnosed PKU have progressive developmental delay in the first year of life, severe mental retardation, seizures, autistic-like behavior and a peculiar odor.

Test: Bacterial inhibition assay to measure blood phenylalanine Using a cut-off level of 4 mg/dL, miss 16% under 24 hours, 2% over 48 hours old

Guthrie bacterial inhibition test: the prototype of metabolic screening tests relying on bacterial inhibition. Filter paper is saturated with heel-stick blood, allowed to dry, small disks are punched out for use in tests. Bacillus subtilis is spread uniformly on agar. Inhibitory amino acid analogs block specific metabolic pathways. Bacterial can grow only if exogenous amino acids competitively overcome the block. Can test in this manner for phenylalanine, leucine, methionine, galastosemia, histidine, and tyrosine. Antibiotics can also inhibit growth, however, causing false negatives.

False positives (1-3% of cases) non-PKU hyperphenylalanemia (1/60,000) pterin defect with secondarily hyperphenylalanemia transient elevation, acute galatosemia False negatives incorrect age, s/p transfusion urine screening unreliable in infants

Genetics Autosomal recessive 1:10,000 to 1:25,000 in US 1:6,000 in Ireland, Scotland and among the Yemenite Jews Frequently seen with biopterin and dihydropteridine reductase deficiencies DNA mutation heterogenous

Pathology Most commonly causes by a deficiency of phenylalanine hydroxylase leading to an accumulation of phenylalanine, which impairs the development of the central nervous system

Diagnosis Rarely diagnosed before 6 months and usually only after mental retardation is obvious Paler and fairer than siblings because melanin formation is competitively inhibited by high phenylalanine levels Progressive developmental delay in the first year of life, severe mental retardation, seizures, autistic-like behavior and a peculiar odor. Hyperactivity and eczema also common.

Treatment Dietary restriction of phenylalanine is highly effective if begun before the infant is 4 weeks old. Diet requires protein restriction and avoidanace of aspartame.

IntroductionIntroduction• Principles of ScreeningPrinciples of Screening• Lessons from the History of Newborn Lessons from the History of Newborn

ScreeningScreening• Some specifics about Maryland NBSSome specifics about Maryland NBS• The Other Controversies in Newborn The Other Controversies in Newborn

ScreeningScreening• Why the heck would anyone Why the heck would anyone refuserefuse

newborn screening newborn screening !?!!?!• Summary and closing points with Summary and closing points with

referencesreferences

• Principles of ScreeningPrinciples of Screening• Lessons from the History of Newborn Lessons from the History of Newborn

ScreeningScreening• Some specifics about Maryland NBSSome specifics about Maryland NBS• The Other Controversies in Newborn The Other Controversies in Newborn

ScreeningScreening• Why the heck would anyone Why the heck would anyone refuserefuse

newborn screening newborn screening !?!!?!• Summary and closing points with Summary and closing points with

referencesreferences

Principles of ScreeningPrinciples of Screening• What makes a test a screening test?

– Diagnostic test used to establish diagnosis– Screening test used to distinguish those who

PROBABLYPROBABLY have have the disorder from those who probablyprobably DON’TDON’T have have the disorder

– A “A “POSITIVEPOSITIVE” screening test must be followed ” screening test must be followed up by a definitive diagnostic test! up by a definitive diagnostic test!

– It’s not the test, it’s how you use it…

Principles of ScreeningPrinciples of Screening• Properties of a good (screening) test

– Cheap and quick

– Accurate and reproducible

– Noninvasive

– Has a good statistical profile• How well the test result predicts the diagnosis

– Positive and Negative Predicitive Values

• How much the diagnosis influences the test result– Sensitivity and Specificity

““The Square”The Square”

AA

True True PositivePositive

BB

False False PositivePositive

CC

False False NegativeNegative

DD

True True NegativeNegative

SensitivitySensitivity = = A/(A+C)A/(A+C)[TP/all those with disease]

SpecificitySpecificity = = D/(B+D)D/(B+D)[TN/all those without disease]

PPVPPV = = A/(A+B)A/(A+B)[TP/all positives]

NPV NPV == D/(C+D)D/(C+D)[TN/all negatives]

DiagnosisDiagnosisDiagnosisDiagnosisTest ResultTest ResultTest ResultTest Result

False positiveFalse positive

True positiveTrue positive

True negativeTrue negative

False negativeFalse negative

100%-PPV100%-PPV

100%-NPV100%-NPV

DiagnosisDiagnosisDiagnosisDiagnosisTest ResultTest ResultTest ResultTest Result

True negativeTrue negative

False positiveFalse positive

True positiveTrue positive

False negativeFalse negative

100%-100%-

SensitivitySensitivity

100%-100%-

SpecificitySpecificity

96% sensitive

98% specific

96% sensitive

98% specific

100% sensitive

80% specific

100% sensitive

80% specific

50% sensitive

100% specific

50% sensitive

100% specific

SensitivitySensitivity vs. vs. SpecificitySpecificity

WA

RW

AR

$20

$20 º

ººº

Height

SensitivitySensitivity vs. vs. SpecificitySpecificity

True NegativeTrue NegativeTrue NegativeTrue Negative False PositiveFalse PositiveFalse PositiveFalse Positive

PPV = TP/(TP+FP)PPV = TP/(TP+FP)

True PositivesTrue Positives

FPFP

980

20PPV = 980/(980+20)

PPV = 98%

PPV = 980/(980+20)

PPV = 98%

1000 1000

2000 patients, ½ with a disease. Lab value discriminates

98% Specific98% Specific 98% Sensitive98% Sensitive


FPFP

98

38PPV = 98/(98+38)

PPV = 72%

PPV = 98/(98+38)

PPV = 72%

1900 100

2000 patients, ½o with a disease. Lab value discriminates

98% Specific98% Specific 98% Sensitive98% Sensitive

PPV = TP/(TP+FP)PPV = TP/(TP+FP)

Limiting the Test PopulationLimiting the Test Population


FPFP

98

2PPV = 98/(98+2)

PPV = 98%

PPV = 98/(98+2)

PPV = 98%

100 100

“Diagnostic” tests have a good PPV because we don’t use them indiscriminantly. If we did, false positives

would increase, PPV would drop and the usefulness of the test would be lost

“Diagnostic” tests have a good PPV because we don’t use them indiscriminantly. If we did, false positives

would increase, PPV would drop and the usefulness of the test would be lost

ScreeningScreening


FPFP

9

2000PPV = 9/(9+2000)

PPV = 0.4%

PPV = 9/(9+2000)

PPV = 0.4%

100000 10

Sens and Spec with a good PPVSens and Spec with a good PPV

• False-negativeFalse-negative “cost”– $$ Cost of treating and

caring for patient– $$ Loss of “productive”

member to society– Emotional burden of living

with a preventable condition

• Would like NONO false negatives

• False-negativeFalse-negative “cost”– $$ Cost of treating and

caring for patient– $$ Loss of “productive”

member to society– Emotional burden of living

with a preventable condition

• Would like NONO false negatives

• Fewer false negatives meansmeans moremore false positives

• False-positiveFalse-positive “cost”– $$ Cost of retesting– $$ Cost of treatment

and/or iatrogenic injury (if started)

– Emotional burden of the “sick-child” syndrome

• Fewer false negatives meansmeans moremore false positives

• False-positiveFalse-positive “cost”– $$ Cost of retesting– $$ Cost of treatment

and/or iatrogenic injury (if started)

– Emotional burden of the “sick-child” syndrome

Minimize False Negatives and False Positives

What kind of things should be What kind of things should be screenedscreened

• Classically– Disorder is silent (no symptoms until irreversible damage done) (PKU)– Intervention is definitive (Diet prevents outcome)

• Current Model– Disorder that can be clinically diagnosed but early

diagnosis is advantageous (MSUD, CAH)– Intervention leads to improved outcome (HbSS)

• Future (constant) consideration?– Can diagnose the currently untreatable

• Opportunity for research, expanding the database• Genetic counseling …

Lessons from history:Lessons from history:THE PPhenylKKetonUUria STORY…

The PKU StoryThe PKU Story• 1934: Borgny Egeland presents Dr.

Asbjörn Fölling with a urine sample (nwbws)

• Isolated Phenylpyruvate

• Still not sure of the physiologic link– But by 1959: shown that a low phenylalanine

diet can improve outcome (case series).– Youngest seems to do best

• Dr. Guthrie develops the “bacterial inhibition assay”– For testing blood levels on patients with PKU during therapy

PKU: the first milestonePKU: the first milestone• Dr. Guthrie takes his message to the streets

– Bypassed medical community– Politicians

• Looking for a magic bullet• Lots of money available• Presidents Advisory Committee

– Popular Press• NY Times• Good Housekeeping

• Emotional and popular push to institute state mandated universal newborn screening

The PKU StoryThe PKU Story• 1963: Mandatory newborn screening

begins in Massachusetts, then Maryland.– 1974: First systematic review of test accuracy

• Found twice as many cases as expected– The problem of assumptions:

• Some MR with hyperPhe all hyperPhe will get MR

– Incidence of HyperPhe in the general “normal” population? Up to 20mg/dL can be “normal”

– How many kids were picked up and treated unnecessarily? At what cost?

PKU: the second milestonePKU: the second milestone• 3 years without a hit in Wash DC

– Quit testing?– Load other tests (cheap)– Payoff for 1:15000 to 1:1500

• By 1975, 43 states mandated screening, None mandated treatment. – Formula gross and expensive and not always

reimbursed

Lessons from the PKU storyLessons from the PKU story

• Assumption about accuracy of test– FP/FN early on

• Assumption about efficacy of treatment– 5 years vs. a lifetime– Does all hyperPhe need to be treated?

• Early analysis focused on dollar-amount cost/benefit– Overly simplistic 50¢ to $100,000– Didn’t account for setup costs– Didn’t account for FOLLOW-UP / TREATMENTFOLLOW-UP / TREATMENT

Lessons from the PKU storyLessons from the PKU story

• Overall feeling is positive, however– Dove in unprepared, but learned to swim as we went– Adjustments have been made– Some information lost to assumptions forever

• “Sneaking” in the infrastructure and mandate makes adding tests VERY easy and cheap– Decreased costs decreased perceived need to show benefit– Which is why we need to be reminded

Lessons from history:Lessons from history:THE SSickle CCell Story STORY…

The HbSS StoryThe HbSS Story• 1970s, Public Health Agencies,

Physicians, African-American Activists, Federal and State governments, for unclear reasons, chose to implement mandatory sickle cell screening laws.– In retrospect, it was not clear what the laws

were hoping to accomplish– Screened were kids and young adults

• Already diagnosed, already “damaged”• No cure

The HbSS StoryThe HbSS Story• Lack of sensitivity to issues of race

– Most early programs targeted “high-risk” population, ie: African-Americans.

– NY State Law: all persons “not of the Caucasian, Indian, or Oriental races” be tested for sickle cell trait before being allowed to obtain a marriage license.

– DC law referred to sickle cell disease as a “communicable disease.”

– National focus on this “most vital health issue” took funds from other programs to fund sickle cell research.

The HbSS StoryThe HbSS Story• Controversy around accuracy and validity

of early screening tests

• Confusion about carrier vs. disease states– Carrier Status associated with:

• Denial of health and life insurance• Denial of employment opportunities• Denial of acceptance into the Air Force academy

– Boycotts of sickle cell screening programs were staged

The HbSS StoryThe HbSS Story• Inadequate protection of the patient’s

rights– Rush to get laws into place left out protective

clauses about• Result confidentiality• Competent genetic counseling• Adequate public education• Guaranteed medical benefits• Universal guidelines for quality control in labs

The HbSS StoryThe HbSS Story• 1980s found that newborn screening could

lead to improved outcome through use of antibiotics and vaccines.– From 5% mortality at 2 years of age to <1%– Decrease in morbidity and mortality compared

to historical cohort.

The Maryland Newborn The Maryland Newborn Screening ProgramScreening Program

MarylandMaryland• Second state to adopt state-wide newborn

screening, after Mass.

• Policies set by the “Advisory Council on Hereditary and Congenital Disorders.”– legislative, medical and consumer members– consumers are the majority

MarylandMaryland• Council considers:

– incidence– cost of treatment– public sentiment– opinions of affected individuals– opinions of psychological, social, ethical and

economic “experts”

• Informed consent

• $15.75 per child, covers all tests

MarylandMaryland• PKU 1965• MSUD 1973• Homocystinuria 1973• Tyrosinemia 1973• Hypothyroidism 1979• Galactosemia 1981/1984• Biotinidase Deficiency 1984• HbSS 1985• CAH 2001• MCADD to be added

(medium chain acyl-CoA dehydrogenase deficiency)

MarylandMaryland Disorder Classic in MD Expected• PKU 1/ 12,712 1/ 15,000• MSUD 1/103,466 1/120,000• Homocystinuria 1/138,852 1/240,000• Tyrosinemia 1/116,056 1/100,000• Galactosemia 1/ 81,426 1/ 40,000• Hypothyroidism 1/ 6,365 1/ 5,000

We’re #1!We’re #1!We’re #1!We’re #1!

The ControversiesThe Controversies• National vs. Regional control

• Leftover Samples

• Informed Consent vs. Dissent

• MS/MS and DNA

The ControversiesThe Controversies• National vs. Regional control

– Universal newborn screening for PKU, CH– Additional test mandated by states, sometimes

for less than reasonable reasons• Very disparate screening programs

– Different states have different incidence of disease based on population

– Dr. Satcher’s equal access to care

The ControversiesThe Controversies• Leftover samples, Leftover samples, ((Maryland informs)Maryland informs)

– Linked (identifiable)Linked (identifiable)• retesting, forensicsretesting, forensics• consent and concern for confidentialityconsent and concern for confidentiality

– Unlinked (anonymous)Unlinked (anonymous)• population studies: drug exposure, genespopulation studies: drug exposure, genes• QA and trying out new testsQA and trying out new tests• right of refusal, concern for true unlinkingright of refusal, concern for true unlinking

– No reports of misuse, yet.No reports of misuse, yet.

The ControversiesThe Controversies• Informed Consent vs. Dissent

– State’s duty to protect it’s citizens vs. Parent’s duty to protect their child

– NAS, 1975 (National Academy of Sciences)• Informed consent

– IOM, 1994 (Institute of Medicine)• Mandatory offering• Informed consent

– Task Force on Genetic Testing, 1997• Informed consent, unless validity and utility of tests are

established

The ControversiesThe Controversies• Informed Consent vs. Dissent

– Wyoming and Maryland are only two states requiring informed consent. Mass for MS/MS

– Maryland study• 5/1000 refused newborn screening• Most moms preferred to be asked prior to testing• Took less than 5 minutes of staff time• Hypothetical advantage for understanding f/u information

including retesting.

The ControversiesThe Controversies• MS/MS and DNA testing

– Testing all babies for all possible things– Charles P. Hehmeyer: malpractice lawyer

• We knowingly kill or injure 1000 kids a year (by not screening) out of 4,000,000 (0.025%)

• Convincing emotional argument, loose with numbers

• March of Dimes: March of Dimes: AnyAny cost is worth it, [HbSS] cost is worth it, [HbSS]

Good of the manyGood of the many Good of the one Good of the one

The ControversiesThe Controversies• MS/MS

– good technology, fewer false positives– amino acids AND/OR acyl carnitines– limited ability to rationally use information, like PKU– Can pick up disease for which

• We can “intervene,” don’t know how useful interventions are• We don’t know if we need to intervene• We can detect but don’t know if they exist in nature

Things we do…Things we do…• These are some examples of tests we use on a

daily basis that evolved into routine practice before we knew how to interpret and act on the results. For the majority of patients we test, we’re still guessing.– Pulse-ox – Electronic Fetal Monitoring– Fetal pulse-ox– Newborn blood glucose– Home apnea monitors

Things we do…Things we do…

Parent RefusalParent Refusal• “…is it true that a hospital can *make* you have a

PKU test done? My mom talked me into getting [my son] a PKU test and I regretted it….it was awful seeing him in pain, and I ALREADY KNEW HE WAS JUST *F I N E*!!!”

• “… just like the other mandatory newborn crap (immunizations, eye meds, etc).”

• The natural screening model

Parent RefusalParent Refusal• Reasons for refusal

– Paranoia (justified or not)• See: HbSS screening

– Leftover samples

• Pain of Heelstick– +/- Incentive to develop less painful procedure given

that it’s a requirement• Can supposedly be done

Parent RefusalParent Refusal• “Sneaking” and “Intimidation”

– When “reason” fails• Move to “SOP” and test baby “by accident”• Threaten that baby can’t leave hospital without test• “It’s the law”

– Arguing about health care is like arguing about religion

• Beliefs are deep and fundamental to the person’s identity

– All states allow for informed parent refusal– Overall, poor form to resist a decision that’s as

informed as it can be

SummarySummary(From the Task Force, 1997)• Infants should benefit from and be

protected by newborn screening systems• Not all conditions are good candidates for

screening– Should occur “often enough” to justify mass screening– Early treatment is effective, accepted and available– Test is simple, safe, valid, precise, acceptable

• Screening is part of a system of follow-up, Screening is part of a system of follow-up, diagnosis, treatment and evaluationdiagnosis, treatment and evaluation

SummarySummary• Infants born anywhere in the US should

have access to screening tests that meet national standards and guidelines.– Data on validity and utility collected through

pilot programs• Public screening programs should not be

implemented until they have first demonstrated their value in well-conducted pilot studies

SummarySummary• Parents, on behalf of their children, have

the right to– be informed about screening– refuse screening– confidentiality and privacy protections

• Parents and consumers must be involved in all parts of the policy-making and implementation process

Pitfalls of Newborn ScreeningPitfalls of Newborn Screening

• Assuming a negative (normal) result on Assuming a negative (normal) result on a newborn screen definitively excludes a newborn screen definitively excludes the conditionthe condition– false negatives are a given in any screening

program– screening tests are NOTNOT diagnostic tests, if

you have suspicions about a disease, test for it


• Not collecting newborn screening Not collecting newborn screening sample prior to transfusion because the sample prior to transfusion because the baby is “too young” or has not yet been baby is “too young” or has not yet been fedfed– Transfusions and feeding history alter results of some,

but not all of the newborn screening tests.– Card has place to list transfusions, time of first

feeding, antibiotics, overall health and birthweight.• Meaningful interpretation of test results takes all those bits of

information into account.


• Not collecting an adequate newborn Not collecting an adequate newborn screening samplescreening sample– Most newborn screening tests are quantitative.

• More or less blood means higher or lower values and may lead to false positives or negatives.

• Diagrams of correct circle filling are meant to ensure that the appropriate amount of blood is on the filter paper, and that there is no evidence of dilution (with alcohol, for example)

Pitfalls of Newborn ScreeningPitfalls of Newborn Screening• Assuming that an abnormal newborn screen Assuming that an abnormal newborn screen

is a false positive because the baby is well is a false positive because the baby is well and/or because factors known to be and/or because factors known to be associated with a false positive are present.associated with a false positive are present.– This runs counter to the whole purpose of newborn

screening, which is to pick up kids BEFOREBEFORE they are symptomatic

– Typical cases:• CH in a preterm infant: often false positives (low T4 then high

TSH), but they MAY have it. Checking TFTs is prudent.• Galactosemia: prematurity, heat-damage, TPN, or antibiotics

may lead to FP. Therapy while awaiting confirmation is easy (lactose-free) but may interfere with breast-feeding.

Questions?Questions?Comments? Criticisms? Anything?Comments? Criticisms? Anything?

Selected References:Selected References:

Newborn Screening Fact Sheets, Committee on Genetics, PEDIATRICS 98(3), Sep 1996, 473-501- summary of metabolic diseases and issues around screening, diagnosing and management

Serving the Family from Birth to the Medical Home, PEDIATRICS 106(2), Aug 2000, 389-426- summary of historical, ethical and practical issues with a call for national standards

Using Tandem Mass Spec for Metabolic Disease Screening Among Newborns- http//www.cdc.gov/mmwr/preview/mmwrthml/rr5003a1.htm

Tyler for Life: http://www.tylerforlife.com/- a nice web site for parents who want to know more about screening

Selected References:Selected References:

Newborn Screening Fact Sheets, Committee on Genetics, PEDIATRICS 98(3), Sep 1996, 473-501- summary of metabolic diseases and issues around screening, diagnosing and management

Serving the Family from Birth to the Medical Home, PEDIATRICS 106(2), Aug 2000, 389-426- summary of historical, ethical and practical issues with a call for national standards

Using Tandem Mass Spec for Metabolic Disease Screening Among Newborns- http//www.cdc.gov/mmwr/preview/mmwrthml/rr5003a1.htm

Tyler for Life: http://www.tylerforlife.com/- a nice web site for parents who want to know more about screening

Documents

Newborn Screening