Psoriasis Workup

Updated: Sep 14, 2022
  • Author: Jacquiline Habashy, DO, MSc; Chief Editor: William D James, MD  more...
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Approach Considerations

The diagnosis of psoriasis is clinical. The differentiation of psoriatic arthritis from rheumatoid arthritis and gout can be facilitated by the absence of the typical laboratory findings of those conditions. Overlap with other arthritic syndromes is possible, however.


Laboratory Studies

Laboratory studies and findings for patients with psoriasis may include the following:

  • Test result for rheumatoid factor (RF) is negative.

  • Erythrocyte sedimentation rate (ESR) is usually normal (except in pustular and erythrodermic psoriasis).

  • Uric acid level may be elevated in psoriasis (especially in pustular psoriasis), causing confusion with gout in psoriatic arthritis.

  • Fluid from pustules is sterile with neutrophilic infiltrate.

  • Perform fungal studies. (This is especially important in cases of hand and foot psoriasis that seem to be worsening with the use of topical steroids.)

If starting systemic therapies such as immunological inhibitors, consider obtaining baseline laboratory studies (ie, complete blood cell [CBC] count, blood urea nitrogen [BUN]/creatinine, liver function tests [LFTs], hepatitis panel, tuberculosis [TB] screening, and pregnancy test).


Other Tests

Although most cases of psoriasis are diagnosed clinically, some, particularly the pustular forms, can be difficult to recognize. In these cases, dermatologic biopsy can be used to make diagnosis. Biopsy of the skin lesion may reveal basal cell hyperplasia, proliferation of subepidermal vasculature, absence of normal cell maturation, and keratinization. A large number of activated T cells are present in the epidermis. Biopsy of acral skin may be less useful as chronic eczematous dermatitis may be psoriasiform and psoriasis  of the palms and soles may show spongiosis more often associated with eczema.

Radiographs of affected joints can be helpful in differentiating types of arthritis. Joint x-rays can facilitate the diagnosis of psoriatic arthritis. Bone scans can identify joint involvement early.

Conjunctival impression cytology has demonstrated an increased incidence of squamous metaplasia, neutrophil clumping, and snakelike chromatin.

When the scales are removed, small droplets of blood appear within a few seconds from exposed vessels in the dermal papillae; this is known as the Auspitz sign.



Punch biopsy of the skin may act as a confirmatory workup procedure.


Histologic Findings

Histopathology findings include the following [38] :

  • Regular acanthosis of the epidermis 
  • Parakeratosis
  • Kogoj spongiotic pustules
  • Munro microabscesses