Serum sickness


Typical appearance of serum sickness rash
  • A type III hypersensitivity reaction (secondary to injection of anitoxins e.g. tetanus, rabies)
  • Reactions secondary to the administration of nonprotein drugs (e.g. Amoxicillin, cefaclor, cephalexin (Keflex), trimethoprim-sulfamethoxazole)
  • Primary occurs 6-21 days after initial exposure
    • 1-4 days after subsequent exposures to the same antigen
  • Symptoms usually last 1-2 weeks before spontaneously subsiding
  • Long-lasting sequelae generally do not occur
  • Fatalities are rare and usually are due to continued administration of the antigen

Clinical Features

Differential Diagnosis


Algorithm for Polyarticular arthralgia


  • Clinical diagnosis in which labs may be suggestive but not required[1]
    • Careful investigation of new medications
    • List of serum sickness medications
  • Mild leukopenia or leukocytosis
  • ESR elevation
  • Mild proteinuria
  • Mild hematuria
  • Mild serum creatinine elevation
  • Decreased C3, C4
  • Other labs to obtain:
    • CH50
    • LFTs
    • Urine electrolytes (Na, K, Cr, eosinophils)
    • ESR and CRP
    • Viral hepatitis panel, HIV, RPR/VDRL



  • Admit for:
    • Significant comorbidities (advanced or very young age, immunocompromised)
    • Severe symptoms
    • Hemodynamic instability/hypotension
    • Unclear diagnosis

External Links

See Also


  1. Alissa HM et al. Serum Sickness Workup. Dec 14, 2015.