Continuity Clinic The Exciting, Emotional and often Misunderstood World of

Continuity Clinic Objectives Identify what makes a screening test effective and its limitations Understand sensitivity, specificity, positive predictive value, and negative predictive value Be familiar with the Virginia Newborn Screen Know how to deal with a positive screening value for hypothyroidism

Continuity Clinic Principles of Screening What makes a test a screening test? –Diagnostic test used to establish diagnosis PROBABLY have probablyDON’T have –Screening test used to distinguish those who PROBABLY have the disorder from those who probably DON’T have the disorder –A “POSITIVE” screening test must be followed up by a definitive diagnostic test! –It’s not the test, it’s how you use it…

Continuity Clinic Principles 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

Continuity Clinic “The Square” A True Positive B False Positive C False Negative D True Negative Sensitivity =A/(A+C) [TP/all those with disease] Specificity =D/(B+D) [TN/all those without disease] PPV = A/(A+B) [TP/all positives] NPV =D/(C+D) [TN/all negatives]

Continuity Clinic DiagnosisDiagnosis Test Result False positive True positive True negative False negative 100%-PPV 100%-NPV

Continuity Clinic What kind of things should be screened 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 …

Continuity Clinic The Virginia Newborn Screening Program

Continuity Clinic Virginia Newborn Screening Services Diagnosed Cases by Disorder 2002

Continuity Clinic 28 Items Screened in VA 1.Congenital Hypothyroidism (CH) 2.Medium-chain acyl-CoA dehydrogenase deficiency 3.Galactosemia 4.Congenital Adrenal Hyperplasia 5.Biotinidase Deficiency 6.Sickle Cell Anemia (Hb SS disease) 7.Maple syrup urine disease (MSUD) 8.Hemoglobin Sickle/Beta-Thal 9.Hemoglobin Sickle/C Disease 10.Homocystinuria 11.PKU Original tests prior to March 2006

Continuity Clinic 28 Items Screened in VA 12.Cystic Fibrosis 13.Argininosuccinic aciduria 14.Beta-Ketothiolase Deficiency 15.Carnitine uptake Deficiency 16.Citrullinemia 17.Glutaric Acidemia type I 18.Isovaleric Acidemia 19.Long Chain hydroxyl-CoA Dehydrogenase Deficiency 20.Methylmalonic acidemia (mutase deficiency) 21.Methylmalonic acidemia 22.Multiple carboxylase deficiency 23.Propionic acidemia 24.Tyrosinemia type I 25.Trifunctional protein defic. 26.Very long chain acyl-CoA dehydrogenase deficiency 27.3-hydroxy 3-methyl glutaric aciduria 28.3-methylcrotonyl-CoA carboxylase deficiency NEW TESTS

Continuity Clinic Summary 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

Continuity Clinic Pitfalls of Newborn Screening Assuming a negative (normal) result on a newborn screen definitively excludes the conditionAssuming a negative (normal) result on a newborn screen definitively excludes the condition –false negatives are a given in any screening program NOT –screening tests are NOT diagnostic tests - if suspecting a disease, test for it!!!

Continuity Clinic Pitfalls of Newborn Screening Not collecting newborn screening sample prior to transfusion because the baby is “too young” or has not yet been fedNot collecting newborn screening sample prior to transfusion because the baby is “too young” or has not yet been fed –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.

Continuity Clinic Pitfalls of Newborn Screening Not collecting an adequate newborn screening sampleNot collecting an adequate newborn screening 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)

Continuity Clinic Pitfalls of Newborn Screening Assuming that an abnormal newborn screen is a false positive because the baby is well and/or because factors known to be associated with a false positive are present.Assuming that an abnormal newborn screen is a false positive because the baby is well and/or because factors known to be associated with a false positive are present. BEFORE –This runs counter to the whole purpose of newborn screening, which is to pick up kids BEFORE 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.

Continuity Clinic Congenital Hypothyroidism The most common case example of the newborn screen at work

Continuity Clinic Newborn Screen for Hypothyroidism Thyroxine (T4) level is measured If T4 level falls in lowest 10% of the results a TSH is measured on same specimen An elevated TSH indicates primary hypothyroidism and the pediatrician is notified

Continuity Clinic Epidemiology Most cases are sporadic – 10-15% are inherited defects –Inherited defects: usually autosomal recessive defects of thyroid hormone production 1/ newborns (in populations with normal iodine nutrition) More common in hispanic and asian populations

Continuity Clinic Back to the Basics

Continuity Clinic Etiology Thyroid Dysgenesis1:4500 –Aplasia, hypoplasia, ectopy Thyroid Dyshormonogenesis1:30,000 Hypothalamic-pituitary deficiency1:100,000 Transient *1:200 Thyroid-binding globulin deficiency1:10,000 * common in areas of iodine deficiency; less common elsewhere and due to antithyroid drug in mom or transplacental thyroid-stimulating hormone antibodies

Continuity Clinic False Positives Blood Transfusion – false elevation of FT4 and false depression of TSH Premature infants – low FT4 as unable to mount TSH surge Perinatal exposure to iodine – betadine during labor or use of iodine containing substance on cord

Continuity Clinic Newborn Screen What do you do if TSH on screen is elevated? –Check serum TSH and FT4 to confirm  The test is a screen not a diagnostic test!!!!!

Continuity Clinic A sign for every office….