What is the role of lab studies in the workup of psoriasis?

Updated: Nov 20, 2020
  • Author: Jacquiline Habashy, DO, MSc; Chief Editor: William D James, MD  more...
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Answer

Testing

There is no specific or diagnostic blood test for psoriasis. Laboratory studies and findings for patients with psoriasis may include the following:

  • Rheumatoid factor level: Negative

  • Erythrocyte sedimentation rate: Usually normal, except in pustular and erythrodermic psoriasis, where it may be elevated along with the white blood cell count

  • Uric acid level: May be elevated in psoriasis (especially in pustular psoriasis)

  • Examination of fluid from pustules: Sterile bacterial culture with neutrophilic infiltrate

  • Fungal studies: Especially important in cases of hand and foot psoriasis that seem to be worsening with the use of topical steroids or to determine if psoriatic nails are also infected with fungus

  • Conjunctival impression cytology: Increased incidence of squamous metaplasia, neutrophil clumping, and snakelike chromatin

The differentiation of psoriatic arthritis from rheumatoid arthritis and gout can be facilitated by the absence of the typical laboratory findings of those conditions.


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