SCID Screen (Severe Combined Immunodeficiency screen) by Flow Cytometry

Immunology

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Description

 Severe Combined Immunodeficiency is a rare but potentially fatal condition of the immune system. Treatment with bone marrow transplantation is more likely to be successful the earlier in life it is given and is most successful in the first 3 months. In 2017 it was suggested by the National Screening Committee that an evaluation into the effectiveness of newborn screening for SCID should be made to increase the number of cases detected early. Currently six Genetic screening centres are taking part in the evaluation (Newcastle, Manchester, Sheffield, Birmingham, GOSH and South East Thames) and further testing by flow cytometry being performed by Immunology laboratories in those regions if required.

A blood spot sample is taken on day 5 of life to test for the number of TRECs (T cell Receptor Excision Circles) via Genetic services. A screen positive result triggers the need for follow up flow cytometry testing to confirm if the patient is has SCID. The markers: CD3, CD19, CD56/16, CD4, CD8, CD45RA, CD27 and HLA DR are used to detect T cells, B cells, NK cells, CD4 T cells, CD8 T cells, naive T cells and MHC II expression.

False positive results will be detected by the blood spot TREC assay therefore normal results will be seen when flow cytometry is performed. Low TRECs can be seen in conditions other than SCID. Any samples with <1500 CD3/uL and naive T cells <70% are abnormal and should be followed up to determine the cause. Non-SCID T cell lymphopaenia in newborns may be secondary to the mother taking immunosuppressive agents, syndromic causes of non-SCID T cell lymphopaenia (eg. DiGeorge) and idiopathic T cell lymphopaenia.

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Indications

Evaluation for the newborn screening for SCID.

Patients older than the newborn screening age who have suspected SCID.  

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Sample Type

2mL EDTA whole blood. Samples must be urgently transported to the laboratory. Requests from outside Sheffield: Please discuss transport requirements prior to requesting this test.

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Reference Range

Flow cytometry normal is defined as >/= 1,500 CD3/µl AND naive T cell >/=70%

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Turnaround Time

<24 hours

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Testing Frequency

By request

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Patient Preparation

Discussion about the test and consent to be taken by Midwives.

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References

PHE Clinical Pathway for babies who screen positive for SCID: https://www.gov.uk/government/publications/clinical-pathway-for-babies-who-screen-positive-for-scid/clinical-pathway-for-babies-who-screen-positive-for-scid SCID Screening Evaluation documents: https://www.gov.uk/government/collections/newborn-blood-spot-screening-programme-supporting-publications scid-screening-evaluation

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Please note: the above information is subject to change and we endeavour to keep this website up to date wherever necessary.