Guidance for primary care clinicians receiving a positive newborn screen result

Other Names

ICD-10 Coding

Disorder Category

Abnormal Finding

Tested By

• TREC test; PCR-based assay that detects the number of TRECs
• Additional testing may be done to confirm the diagnosis and determine the type of SCID, which will determine next steps in management.

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 may be absent or compromised. Impairment of both B and T cells leads to the term “combined.” In certain presentations, NK cells may also be affected in about 50% of patients with SCID. 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).
• Refer the patient to the pediatric bone marrow transplant (BMT) group.
• Until testing is complete, avoid exposing the infant to those who are sick and large groups.
• 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 risk of transfer of CMV from breastmilk. Some treatment centers recommend stopping breastfeeding/breastmilk unless the mother is known to be CMV-negative and will continue to monitor the mother for potential CMV infections when using breastmilk.
• 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 NM providers [3])
  • Pediatric Allergy (see NM providers [8])
  • Pediatric Immunology (see NM providers [3])
  • Pediatric Infectious Disease (see NM providers [2])
• Patients with positive newborn screening for SCID need to be referred to the Pediatric Bone Marrow Transplant group for further workup and management.
• Confirmatory testing done by pediatric BMT 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 a 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 genetic variants associated with SCID. Commonly, testing for transplacental maternal engraftment of T cells is performed.

If the Diagnosis is Confirmed

• After a positive newborn screening test for SCID, the patient will be connected with the pediatric BMT group who will be able to assist the family with management and treatment options and, if needed, discuss hematopoietic stem cell transplant.
• Educate the family about signs, symptoms, and need for urgent care when the infant becomes ill before being seen by the BMT group.
• Provide the family with basic information about SCID and T-cell lymphopenia.• Provide the family with basic information about SCID and T-cell lymphopenia.