What is the role of lab tests in the workup of priapism?

Updated: Dec 26, 2019
  • Author: Osama Al-Omar, MD, MBA, FACS, FEBU; Chief Editor: Edward David Kim, MD, FACS  more...
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A complete blood cell count (CBC) should be performed to determine whether the patient has anemia, leukocytosis, or thrombocytosis. Rarely, the CBC will identify undiagnosed leukemia as the cause of priapism.

Patients with sickle cell disease should have a CBC and a reticulocyte count. If sickle cell status is unknown, a hemoglobin S determination may be useful. Patients with sickle cell disease may also need a blood type and screen performed in case transfusion or plasma exchange is necessary.

Measurement of plasma thromboplastin or activated partial thromboplastin time to determine coagulation status may be useful, as priapism may require surgical intervention if medical treatment fails.

Penile blood gas (PBG) test results allow differentiation between high- and low-flow priapism. Low-flow PBG findings may include a pH of less than 7.0, a PCO2 of greater than 60 mm Hg, and a PO2 of less than 30 mm Hg. Variation depends on the duration of the episode. High-flow PBG findings should reflect normal arterial values.

Urine toxicology and psychoactive medication screening should be considered, in suspected patients, as some of these medications are known to cause priapism in standard doses or overdoses.

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