Pediatric Chronic Granulomatous Disease Workup

Updated: Aug 07, 2019
  • Author: Lawrence C Wolfe, MD; Chief Editor: Cameron K Tebbi, MD  more...
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Workup

Laboratory Studies

The following tests are indicated in chronic granulomatous disease (CGD):

  • Nitroblue tetrazolium (NBT) test

    • The standard assay for phagocytic oxidase activity is the NBT test. The colorless compound NBT is reduced to blue formazan by the activity of the phox enzyme system. Several versions of the test exist; each has advantages and disadvantages.

    • The most efficient and informative version is the NBT slide test, in which a drop of whole blood is placed on a microscope slide coated with an activating agent, such as lipopolysaccharide or phorbol ester. Phagocytes adhering to the slide are activated and develop blue inclusions on incubation with NBT. The number of NBT-positive cells is scored under a microscope. This test is often preferred because of the small amount of blood required and the lack of a need for specialized equipment. Although the result is nonquantitative, an experienced technologist can differentiate normal phagocytes reliably from low-level phox activity observed in some cases of p47 deficiency.

    • The NBT test can be useful in identifying X-linked carrier female individuals when peripheral phagocytes consist of 2 cell populations: one that reduces NBT to formazan and one that does not.

    • The NBT is limited by its subjectivity, need for experienced technician, and false-negative results that cause the diagnosis of chronic granulomatous disease to be missed. False-negative findings occur when formazan accumulates in cells with low levels of active adenine dinucleotide phosphate (NADPH) oxidase. These patients clinically have the disease, but their NBT test results are negative.

    • In an alternative technique, leukocytes are isolated from blood and incubated with NBT in a test tube. Formazan is solubilized by addition of an organic solvent, and the blue color intensity is read by a spectrophotometer.

  • Dihydrorhodamine (DHR) test

    • This flow cytometric test is now widely and commercially available and should be considered the preferred screening and diagnostic test for chronic granulomatous disease. This test should be considered the most accurate diagnostic test for chronic granulomatous disease.

    • Phagocytic cells reduce DHR to the strongly fluorescent compound rhodamine. Individual fluorescent cells can then be counted, and the amount of fluorescence per cell is quantified with flow cytometry.

    • This test combines the best features of the slide and tube NBT tests, although a specialized instrument is required.

    • Deficiencies of gp91 (no activity, no DHR conversion) and p47 (low activity, minimal DHR conversion) can be distinguished with this method. X-linked carriers of chronic granulomatous disease can also be identified with the DHR test.

  • Genetic testing

    • Specific gene mutation is useful to establish the genetic inheritance pattern and aid in family counseling. Although the family history is sometimes informative in cases of X-linked chronic granulomatous disease (X-CGD), the high incidence of new mutations and the appearance of male subjects with autosomal recessive mutations make some type of laboratory confirmation important.

    • The low incidence of chronic granulomatous disease and the large number of unique mutations preclude standardized genetic testing. Therefore, individual genetic analysis remains the domain of specialized research laboratories.

    • Mutations can currently be identified in nearly all patients and in about 90% of mothers of affected children.

    • Identification of the precise molecular defect in individual patients takes on added importance with the recent initiation of gene-therapy trials in chronic granulomatous disease.

  • Other tests

    • When screening results are inconclusive or when additional confirmation is required, other assays of phagocyte oxidative metabolism can be performed in research laboratories capable of studying phagocytes.

    • On Western blot analysis, failure to detect the p22, p47, or p67 products can be taken as evidence of autosomal recessive mutation in the corresponding gene.

  • Prenatal diagnosis

    • Prenatal diagnosis for siblings of affected patients can be achieved in one of two ways. When a mutation is precisely identified in the affected child, chorionic villus biopsy can be performed to obtain enough DNA to identify affected fetuses. As an alternative, dinucleotide repeat polymorphisms linked to the CYBB gene may be useful in the prenatal diagnosis of X-CGD.

    • When these DNA detection methods are not available, fetal blood can be sampled and an NBT slide test performed.

    • Chorionic villus sampling is technically preferred because of its applicability early in gestation and the reduced risk of fetal loss.

    • If parents are not considering termination of a pregnancy, newborns can be tested by using the slide NBT or flow cytometric DHR tests because affected fetuses do not appear to be at increased risk of infection in utero.

  • Other laboratory findings

    • Other than the specific tests of phagocyte oxidative metabolism that help in establishing the diagnosis, no consistent or characteristic laboratory findings define this disease.

    • Most patients have WBC counts that are within the reference range or elevated, with further increases during infectious episodes.

    • Phagocyte morphology, phagocytic cell-surface adhesion proteins, chemotaxis, and phagocytosis are normal.

    • Patients may have anemia of chronic disease.

    • The erythrocyte sedimentation rate can be elevated even between infections.

    • Hypergammaglobulinemia is a common feature of the illness and is believed to represent a host response to recurrent or persistent infection.

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Imaging Studies

Imaging studies such as chest radiography and CT imaging are valuable in the diagnosis and management of pulmonary and hepatosplenic infections.

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Histologic Findings

The two most frequent findings on histologic examination of the lesions observed in chronic granulomatous disease are infection and postinfectious granulomas.

Frequent sites of infection are the skin, lymph nodes, lungs, liver, spleen, bones, and joints; the brain and the GI and genitourinary (GU) tracts are less commonly involved.

Histologic findings consist of suppurative lesions with collections of phagocytic cells, predominantly neutrophils, with the causative bacteria or fungi and abscess formation.

Granulomatous involvement of the GI and GU tracts is not uncommon. Biopsy of these lesions shows necrotic granulomas with pigmented histiocytes and macrophages. These are most often sterile.

Similar granulomatous infiltrations of the skin and lungs are described.

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