What is the role of lab tests in the workup for Shwachman-Diamond syndrome (SDS)?

Updated: Nov 17, 2020
  • Author: Antoinette C Spoto-Cannons, MD, FAAP; Chief Editor: Hassan M Yaish, MD  more...
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Answer

See the list below:

  • CBC to assess neutropenia, anemia, and thrombocytopenia

    • Cyclic or persistent neutropenia is observed in 88-100% of patients with Shwachman-Diamond syndrome (SDS). [61, 62, 63, 6, 64, 52] Because the neutropenia may be intermittent, CBC counts may need to be repeated biweekly over a 3-week period to document neutropenia. [65]

      • Neutropenia is defined as an absolute neutrophil count (ANC) of less than 1500/mcL in whites and less than 1200 in blacks. See the Absolute Neutrophil Count calculator.

      • Mild neutropenia is defined as an ANC of 1000-1500/mcL.

      • Moderate neutropenia is defined as an ANC of 500-1000/mcL.

      • Severe neutropenia is defined as an ANC of less than 500/mcL.

    • Anemia is present in more than 50% of patients with Shwachman-Diamond syndrome secondary to iron deficiency and/or bone marrow hypoplasia.

    • Thrombocytopenia is present in more than 25% of patients with Shwachman-Diamond syndrome.

    • A CBC count should also be obtained every 3-6 months or as clinically indicated. [66]

  • Neutrophil function studies: A neutrophil migration defect may be documented.

  • Fetal hemoglobin: This is elevated in approximately 80% of patients with Shwachman-Diamond syndrome. [31]

  • Iron, folate, and vitamin B12 levels: Patients may have associated iron, folate, or vitamin B12 deficiency secondary to malabsorption. Obtain at time of diagnosis and as clinically indicated. [66]

  • A 72-hour fecal fat measurement:

    • An increase in fecal lipids and fatty acids is present in persons with Shwachman-Diamond syndrome.

    • The fecal fat losses vary from 3-60%, and these losses decrease with age. After an individual with Shwachman-Diamond syndrome is aged 8 years, fecal fat losses average 8% of intake. [67] This decrease in fecal fat losses may be related to the patient's increasing pancreatic secretion of lipase coupled with the decreased dietary fat with age.

    • The absence of steatorrhea does not exclude the diagnosis of Shwachman-Diamond syndrome. [10]

  • Secretin-cholecystokinin quantitative stimulation test: Pancreatic insufficiency is evidenced by the absence or decrease of trypsin, lipase, colipase, and amylase activities in pancreatic secretions from less than 2% to approximately 10-14% of the reference range after quantitative stimulation test with intravenous secretin and cholecystokinin. [5] Obtain at time of diagnosis and as clinically indicated. [66]

  • Sweat test: In individuals with Shwachman-Diamond syndrome, this test demonstrates no increase in chloride, in contrast to cystic fibrosis, in which the chloride level is abnormally elevated; however, false positives have been reported. [68, 69] The test should be repeated if there is any doubt regarding the diagnosis. [69]

  • Glucose tolerance test: These findings are generally normal. Rarely, patients with Shwachman-Diamond syndrome may have diabetes mellitus.

  • Urinalysis: In persons with Shwachman-Diamond syndrome, urinalysis reveals inconsistent galactosuria with the presence of reducing substances but without glucosuria.

  • Serum bicarbonate, PCO2, hydrogen ion concentration (H+), and urinary pH: Measured simultaneously, these may suggest renal tubular acidosis.

  • Liver function tests

    • Transaminases (ie, alanine aminotransferase, aspartate aminotransferase) may be elevated in individuals with Shwachman-Diamond syndrome. [70]

    • Alkaline phosphatase may be within the reference range or slightly increased.

    • Findings on coagulation studies are normal, and the serum bilirubin level is within the reference range.

    • Hypoalbuminemia may be present secondary to malabsorption.

    • These should be obtained at time of diagnosis and as clinically indicated. [66]

  • Immunoglobulin levels: Immunoglobulin A (IgA), IgM, and/or immunoglobulin G (IgG) levels may be low. Obtain at time of diagnosis and as clinically indicated. [66]

  • Growth hormone levels: These are often decreased in persons with Shwachman-Diamond syndrome.

  • Vitamin A, D, E and K levels: These may be low due to malabsorption. [63] Obtain vitamin A, D, and E and prothrombin time at time of diagnosis, one month after initiation of pancreatic enzyme therapy, then every 6-12 months. [66]

  • Serum calcium and phosphorous: These levels are within the reference range.


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