Some babies need to have the newborn screening test repeated. The baby’s midwife or the hospital where the baby was born should organize the repeat newborn screen.
Reasons a baby may need a repeat newborn screen
1. The first newborn screening sample was “unsatisfactory”
This means that the sample could not be tested properly. A sample could be unsatisfactory because:
- the newborn screen was taken too soon, before 24 hours of age;
- the newborn screening card was not filled out properly;
- the sample was received at Newborn Screening Ontario (NSO) more than two weeks after it was taken;
- there was not enough blood to test;
- the quality of the blood sample was too low to test;
- the sample was damaged in transit;
- the sample was mislabeled.
When a baby’s sample can not be properly tested, a repeat sample is needed as soon as possible to perform newborn screening.
2. The baby had a Packed Red Blood Cell Transfusion (PBRC) before their first newborn screening sample was taken
A blood transfusion is when a person gets blood that comes from someone else. Some babies need a blood transfusion if they are sick. Only the type of transfusion called a Packed Red Blood Cell (PRBC) transfusion affects the newborn screening test. Testing for most diseases is accurate even if a baby had a transfusion before his or her newborn screening test. However, PRBC transfusions interfere with newborn screening for galactosemia and the hemoglobinopathies. To accurately screen for these diseases, a repeat newborn screen is needed 4-6 months after the baby’s last PRBC transfusion. For example, if a baby had transfusions at 1 day of age, 2 weeks of age, and 6 weeks of age the repeat newborn screen should be taken 4-6 months after the 6 week transfusion.
If your baby had a PRBC transfusion, please review our transfusion information sheet for more information.
3. The baby was born at less than 33 weeks gestational age and/or had a birth weight of less than 1500g
Babies born before 33 weeks gestational age and/or who have a very low birth weight (less than 1500 grams) may have inaccurate newborn screening results on their first sample and require a repeat newborn screening sample at 3 weeks of age. Testing for most diseases is accurate even when a baby is premature and/or very low birth weight. However, significant prematurity and/or very low birth weight can affect newborn screening results for Congenital Hypothyroidism (CH) and Severe Combined Immune Deficiency (SCID). To accurately screen a baby for these diseases, he or she needs a repeat newborn screen at 3 weeks of age. If a baby is discharged from hospital prior to 3 weeks of age, a repeat sample may be taken at the time of discharge or the parents may be asked to return to the hospital for a repeat newborn screen.
If your baby was significantly premature or had a very low birth weight, please review our prematurity/low birth weight information sheet for more information.