Guidance for primary care clinicians receiving a positive newborn screen result

Other Names

ICD-10 Coding

Disorder Category

Abnormal Finding

Tested By

Severe combined immunodeficiency (SCID) includes a group of rare, but serious and potentially fatal inherited immune disorders in which T lymphocytes fail to develop and B lymphocytes either are absent or compromised. Impairment of both B and T cells leads to the term “combined.” Untreated patients develop life-threatening infections. The screening test for TRECs, a byproduct of normal T-cell development, identifies SCID and some related conditions with low T cells that result in less severe immunodeficiency. Some infants with mild to moderately low TRECs have a transient lymphopenic condition related to delay in maturation of the immune system, which can be more common in the neonatal intensive care unit /premature infant population.

Clinical Characteristics

Incidence

Inheritance

Next Steps After a Positive Screen

• Contact the family to inform them of the newborn screening result. Point out that additional tests are required to determine whether the baby actually has an immune deficiency (1:10-1:20 of abnormal SCID screening tests in Utah that require confirmatory testing are consistent with SCID). The remainder of abnormal screening tests may include infants with mild-to-moderate immune defects, those with transient delays in T-cell maturation, or those with false-positive tests).
• Until testing is complete, avoid exposing the infant to those who are sick.
• If the infant has any signs of illness, refer to a pediatric hospital right away for evaluation and potential administration of immune globulin and antibiotics.
• If the infant requires transfusion of any blood product, be sure that only leukocyte-reduced, irradiated products that are negative for cytomegalovirus (CMV) are used.
• There is a theoretical risk of transfer of CMV from breastmilk. Some treatment centers recommend stopping breastfeeding/breastmilk unless mother is known to be CMV-negative.
• DO NOT give live attenuated rotavirus vaccine, which could cause infection and prolonged diarrhea in a baby with SCID. This vaccine is to be given only after an immunology specialist confirms that the baby’s immune system is normal.

Confirming the Diagnosis

• To confirm the diagnosis of SCID, work with Newborn Screening Services (see NW providers [1]) Pediatric Allergy (see NW providers [1]) Pediatric Immunology (see NW providers [0]) Pediatric Infectious Disease (see NW providers [0]).
• Confirmatory testing after an abnormal screening result will include lymphocyte subset enumeration of T, B, and NK cells.
• If there are further concerns of SCID or other immune deficiency, full characterization of the immune system will include complete blood count with differential lymphocyte subset enumeration of T, B, and NK cells, antibody levels, lymphocyte proliferation to mitogens, and molecular genetic testing for specific gene diagnosis. In some cases, chimerism studies are completed since some infants with SCID acquire maternal lymphocytes in utero.

If the Diagnosis is Confirmed

• Consult with a specialist in pediatric immunodeficiency diseases who will be able to assist the family with treatment options and, if needed, a bone marrow transplant.
• Educate the family about signs, symptoms, and the need for urgent care when the infant becomes ill.
• Provide the family with basic information about SCID and T-cell lymphopenia.• Provide the family with basic information about SCID and T-cell lymphopenia.