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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

Doxepin, a tricyclic antidepressant (TCA) with antihistaminic properties, at dosages of 25-50 mg at bedtime may be quite helpful. Mirtazapine at 15-30 mg at bedtime has also been effective. Please consult your doctor before using any medication.


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wishing you best of health

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