Therefore, SCID should be considered an immunologic emergency, requiring rapid referral to a medical center where therapy can be initiated. If transplantation is delayed past 6 months of age, the survival rate falls to <50%, generally due to opportunistic infections or non-engraftment. This test can be performed using small volumes of blood (90%. The most effective screening test for SCID is a lymphocyte subset analysis using flow cytometry to enumerate the proportion of T cells, B cells and natural killer (NK) cells in the peripheral blood. A caveat is that some subsets of patients with SCID have severe lymphopenia, thus providing a clue to the diagnosis based on a complete blood count (CBC) that shows an absolute lymphocyte count of less than 1000 cells/μL. However, SCID must be specifically suspected because common laboratory testing, such as complete blood counts, comprehensive metabolic panels, and urinalysis, often will produce normal or near-normal results. What laboratory studies should you request to help confirm the diagnosis? How should you interpret the results?Īny infant or child who has clinical conditions suggestive of SCID can be easily screened, and in most cases laboratory results will quickly lead to a diagnosis. Malnutrition and parental neglect can also mimic the clinic manifestations of SCID.Ī focused laboratory evaluation often quickly differentiates SCID syndromes from these other conditions. Many inborn errors of metabolism and genetic conditions such as cystic fibrosis have clinical characteristics similar to SCID because of the common association of FTT with recurrent infections. The most common T cell deficiency in children worldwide remains perinatally acquired HIV infection, and children with AIDS have clinical courses very similar to SCID. CGD is characterized by infections with catalase positive organisms such as Staphylococcus aureus and Aspergillus, although infections with atypical Mycobacteria and Nocardia can be seen in either CGD or SCID. Antibody deficiencies generally become apparent in older infants following the decay of transplacentally derived maternal IgG, but these patients can also have viral and bacterial infections that mimic SCID. The most common include defects in B cell development, including X-linked agammaglobulinemia (XLA), X-linked hyper IgM (XLHIGM), or chronic granulomatous disease (CGD). There are several primary immune deficiencies that share clinical features of SCID. What other disease/condition shares some of these symptoms? Infants with ectodermal dysplasia with immune deficiency have abnormal hair and malformed conical teeth, in addition to recurrent infections. Patients with Wiscott-Aldrich syndrome, a form of combined immune deficiency, have a distinct clinical phenotype of eczema, thrombocytopenia and recurrent infections. Some forms of SCID, such as Omenn syndrome, display erythroderma and eosinophilia that are manifestations of immune dysregulation. However, most infants with SCID appear normal at birth with no obvious physical findings or signs that would raise clinical suspicion. These infants display chronic inflammatory dermatitis, hepatitis, and diarrhea. On the other hand, in some cases the clinical manifestations can be indolent, consisting of failure to thrive (FTT), intestinal malabsorption due to chronic viral or parasitic infections, or persistent rash and hepatitis due to either chronic viral infection or graft-versus-host-disease (GVHD).Īpproximately 20% of patients with SCID will exhibit maternally derived GVHD, the result of transplacental transfer of maternal lymphocytes that are able to proliferate freely in the immune incompetent host.
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