What is the role of lab tests in the workup of Henoch-Schönlein purpura (IgA vasculitis)?

Updated: Oct 28, 2020
  • Author: Rajendra Bhimma, MBChB, MD, PhD, DCH (SA), FCP(Paeds)(SA), MMed(Natal); Chief Editor: Craig B Langman, MD  more...
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Answer

No specific diagnostic laboratory test is available to assess for markers of IgAV. General laboratory tests may reveal the following:

  • Antinuclear antibody (ANA) and rheumatoid factor (RF) - Absent
  • Factor XIII - Reduced in about 50% of patients
  • Urinalysis - Hematuria; proteinuria may also be found
  • CBC - Leukocytosis with eosinophilia and a left shift; thrombocytosis is present in 67% of patients
  • Platelet count - May be elevated; low platelet levels suggest thrombocytopenic purpura
  • Erythrocyte sedimentation rate (ESR) - Variably elevated; may be mildly elevated in as many as 75% of patients
  • Stool guaiac test - May reveal occult blood [89]
  • Blood urea nitrogen (BUN) and creatinine - May be elevated, indicating decreased kidney function
  • Amylase and lipase - May be elevated in patients with pancreatitis
  • Electrolytes - Generally in the reference range, but may be affected by excessive vomiting (eg, hypokalemia, hypochloremia)
  • Plasma D-dimer - May be substantially increased
  • Plasma thrombin-antithrombin (TAT) complex, prothrombin fragment (PF)–1, and PF-2 - May be abnormal
  • Prothrombin time (PT) and activated partial thromboplastin time (aPTT) - May be reduced (eg, hypoprothrombinemia)
  • Serum immunoglobulin A (IgA) - Increased in 50-70% of patients during the acute phase of illness; higher levels are associated with kidney involvement; circulating IgA immune complexes may be present in some patients, though data supporting the presence of classic antigen-antibody complexes have been questioned
  • Factor VIII - Decreased in some patients
  • Antistreptolysin O (ASO) - Elevated in 30% of patients
  • Complement studies - CH50 is decreased in 30% of patients; C3 and C4 are occasionally decreased
  • Immunocomplexes of IgG and IgA - May be increased

Total IgA levels are not very helpful in confirming the diagnosis or providing prognostic information. Elevated serum levels of galactose-deficient IgAseem to distinguish IgAV patients with nephritis from those without nephritis, but this assay is not used presently in clinical practice. [90, 91]


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