Pruritus and Systemic Disease Workup

Updated: Mar 03, 2020
  • Author: David F Butler, MD; Chief Editor: William D James, MD  more...
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Laboratory Studies

When a primary dermatologic condition is excluded and a systemic cause is suspected, certain laboratory tests may aid diagnosis. If suspicion is low concerning a systemic disease, a 2-week trial of therapy with oilated soap for bathing, emollients for after the bath, and oral antihistamines may be attempted. If this fails, a laboratory evaluation is indicated.

The following screening laboratory tests are recommended:

  • CBC count with differential: This test assists in uncovering polycythemia vera, in which the hemoglobin level, hematocrit value, WBC count (including absolute neutrophil count; see the Absolute Neutrophil Count calculator), and platelet count are elevated. Abnormalities are also seen in persons with hematologic malignancies. Patients with iron deficiency may have microcytosis and low hemoglobin levels. However, those with pruritus and iron deficiency may not be anemic; tests of and serum iron, ferritin, and total iron-binding capacity may be ordered to confirm or exclude the diagnosis.

  • Serum creatinine and blood urea nitrogen values: Persons with CRF have elevated levels.

  • Serum alkaline phosphatase and bilirubin, direct and indirect: Elevated levels may suggest cholestasis. If elevated, antimitochondrial antibody and serum anti–hepatitis C tests may be ordered to confirm primary biliary cirrhosis and hepatitis C, respectively, if these are suspected. Other tests may be needed to confirm other causes of cholestasis. A positive antimitochondrial antibody finding has 98% specificity for primary biliary cirrhosis.

  • Thyrotropin and thyroxine: The results assist in ruling out hypothyroidism and hyperthyroidism.

  • Fasting glucose value, if prompted by signs or symptoms

  • Stool for occult blood in patients aged 40 years or older: A positive result suggests possible malignancy in the GI tract.

  • HIV antibody test, if risk factors are present

  • Skin biopsy for routine pathology and immunofluorescence to exclude subacute occult autoimmune conditions such as pemphigoid and dermatitis herpetiformis


Imaging Studies

In patients with Hodgkin disease, chest radiography may help in detecting lymphadenopathy in the mediastinum. If cholestasis is present, abdominal ultrasonography may be performed to evaluate the biliary tract.


Other Tests

When the results of initial laboratory screening are negative and when the physician still suspects a systemic cause, tests of the following may be ordered:

  • Serum protein electrophoresis

  • Stool for ova and parasites

  • Stool for occult blood (may reveal source for anemia)

  • Urine for hydroxy indole acetic acid (5-HIAA) and mast cell metabolites

Negative findings from the initial evaluation do not necessarily exclude systemic disease, and follow-up screening may be repeated every 3-6 months if clinical suspicion continues.



Endoscopic retrograde cholangiopancreatography should be performed when primary sclerosing cholangitis, choledocholithiasis, or obstructive malignancy is suspected.

Skin biopsy for direct immunofluorescence and special stains may help exclude a primary dermatologic condition, such as dermatitis herpetiformis or bullous pemphigoid (ie, pruritic pemphigoid), or confirm a systemic cause, such as in mastocytosis.


Histologic Findings

Because skin lesions are most likely secondary to scratching, biopsy reveals nonspecific findings. Histologic features may include a hyperkeratotic epidermis with acanthosis and parakeratosis and elongation of the rete ridges. A perivascular lymphoid infiltrate may be present.