Down syndrome laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Dildar Hussain, MBBS [2]


Down syndrome is confirmed through cytogenetic studies which confirm trisomy 21. In addition complete blood count with differentials is performed to rule out leukemia, TSH and T4 are performed at birth, 6 months, 1 year and then annually to rule out hypothyroidism. Low level of IgG subclass 4 are correlated with bacterial infections. The mosaic trisomy 21 includes lymphocyte preparations, FISH, buccal mucosa cellular preparations and scoring frequency of trisomic cells.

Laboratory Findings

  • The following lab tests are done for the patients of Down syndrome to rule out conditions associated with down syndrome:[1][2]
    • CBC with differentials to rule out Leukemia
    • To rule out hypothyroid, the following tests are performed at birth, 6 months, 1 year and then annually:
    • Cytogenetic studies
    • Measurement of Immunoglobulin G
      • Subsequent low level of IgG subclass 4 are correlated with bacterial infections
    • The Mosaic trisomy 21 that includes:
    • Interphase fluorescence in situ hybridization (FISH)
      • Interphase fluorescence in situ hybridization is used for early and rapid detection of trisomy 21
      • The FISH test is beneficial in the diagnosis of Down syndrome in prenatal and neonatal period
      • The FISH test needs to be confirmed by a complete karyotype analysis as it does not provide information about the trisomy 21 to weather if it is secondary to a translocation


  1. Ringman JM, Rao N, Lu PH, Cederbaum S. Mosaicism for trisomy 21 in a patient with young-onset dementia. A case report and brief literature review. Arch Neurol. 2008. 65:412-415.
  2. Papavassiliou, Paulie; York, Timothy P.; Gursoy, Nurcan; Hill, Gloria; Nicely, Lauren Vanner; Sundaram, Usha; McClain, Allison; Aggen, Steven H.; Eaves, Lindon; Riley, Brien; Jackson-Cook, Colleen (2009). "The phenotype of persons having mosaicism for trisomy 21/Down syndrome reflects the percentage of trisomic cells present in different tissues". American Journal of Medical Genetics Part A. 149A (4): 573–583. doi:10.1002/ajmg.a.32729. ISSN 1552-4825.

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