Disorders Screened and Test Accuracy

1. What disorders does the newborn screen detect?
2. Why screen for these disorders and not others?
3. What are the possible results of a newborn screen?
4. What is the process if a baby has a “positive screen” for one of these disorders?
5. What is the process if a baby is identified as a cystic fibrosis (CF) carrier or as having a hemoglobinopathy trait?
6. If parents wish to have carrier testing for CF or hemoglobinopathy screening, what is the process?

7. Will the newborn screening test identify disorders other than the 22 targeted disorders?
8. How accurate are the newborn screening tests?

1. What disorders does the newborn screen detect?

• BC's Newborn Screening Program screens for 22 disorders.
• CAH screening was added in the fall of 2010.

• The disorders on the screening panel were selected by the Newborn Screening Advisory Committee of BC following an evidence-based review process.
• Factors considered in the decision process included: incidence and seriousness of the disorder, evidence of improved health outcomes with early detection, test performance (accuracy and reliability), availability of confirmatory testing and follow-up treatment.
• The Newborn Screening Advisory Committee will review the panel of screening tests periodically and recommend changes as new tests and/or information about disorders becomes available.

• “Negative screen” for all disorders. The NBS Laboratory will send a “negative screen” report to the physician/midwife listed on the blood spot card and to the baby’s birth hospital.
• "Repeat sample requested". The NBS Laboratory will send a report to the physician/midwife listed on the blood spot card to request a repeat sample. A copy of the report will be sent to the baby’s birth hospital. Usual reasons are:
• Baby was less than 24 hours old at the time of collection;
• Baby was less than 1,500 grams at birth;
• Baby had a blood transfusion prior to collection of the sample; or
• Sample was unsatisfactory.
• “Positive screen” for one of the disorders. A positive screen does not mean that the baby has a disorder, but only that further testing is required. See question #4.
• Baby is a “CF carrier” or has a hemoglobinopathy “trait.” See questions #5 and #6.

Back to Top

4. What is the process if a baby has a “positive screen” for one of these disorders?

• The NBS Laboratory will contact the baby’s physician/midwife by phone to discuss the positive screen and coordinate the next steps.
• Generally, the physician/midwife will be asked to contact the family to assess the clinical state of the baby and organize the repeat testing. Contact information for an appropriate specialist on-call will also be provided in cases in which there are immediate clinical concerns.
• The NBS Laboratory will contact the baby’s physician/midwife with the repeat testing results as soon as they are available and will coordinate referral to the appropriate clinical specialty if the repeat results are positive.

• Screening for cystic fibrosis and hemoglobinopathies may identify a baby that is a CF carrier or has a hemoglobinopathy trait.
• It is important for the parents to know if the baby is a CF carrier or has a hemoglobinopathy trait so they can:
• Tell their child later in life. His or her future partner can choose to have testing to identify the couple’s chances of having a baby with CF, or a clinically significant hemoglobinopathy.
• Decide whether they wish to be tested. If the baby is a CF carrier or has a hemoglobinopathy trait, one parent is almost certainly a carrier. There is a small risk that both parents are carriers which would have implications for future pregnancies.
• Resources are available to assist in counseling families with regards to these issues. Referral to the BC Medical Genetics program (see question #6) for genetic counseling may also be appropriate under some circumstances.

Back to Top

6. If parents wish to have carrier testing for CF or hemoglobinopathy screening, what is the process?

• Pre-test counselling and testing can be done by the physician.
• If parents wish additional genetic counselling, the physician may refer them to the Provincial Medical Genetics Program in Vancouver (604-875-2157) or Vancouver Island Medical Genetics in Victoria (250-727-4461).
• Questions from physicians and nurses about carrier testing and the interpretation of results may be directed to a genetic counsellor in one of the Medical Genetics clinics listed above.

• Ten secondary disorders that are not primary targets of the screening program may be identified as “byproducts” of the screening process:
• a. Amino Acid Disorders
• i. Hypermethioninemia (MET)
• ii. Citrin Deficiency (CIT II)
• iii. Mild Hyperphenylalaninemia (H-Phe)
• iv. Biopterin Biosynthesis Defects (BIOPT BS)
• v. Biopterin Recycling Defects (BIOPT REC)
• b. Organic Acid Disorders
• i. Cobalamin C/D (Cbl C/D)
• ii. 2-methylbutyrylglycinuria (2MBG)
• c. Fatty Acid Oxidation Disorders
• i. Trifunctional Protein Deficiency (TFP)
• ii. Multiple Acyl-CoA Dehydrogenase Deficiency (MAD)
• d. Hemoglobinopathies
• i. Variant Hemoglobinopathies (Var Hb)

Back to Top

8. How accurate are the newborn screening tests?

• Screening for some of the new disorders (MSUD, Hcy, CAH, PROP, MUT, CbIA,B) will be introduced in two phases. First tier testing (phase 1) began in November 2009 and second tier testing with additional analytes (markers) was added in the fall of 2010.
• The “second tier” tests are performed on the original blood sample when the first screen is abnormal. Second tier testing will increase the:
• a. sensitivity (proportion of cases detected); and
• b. positive predictive value (PPV; percentage of babies with a positive screen that truly have the disorder).
• Sensitivity and Positive Predictive Value Table

Updated: December 16, 2010