- Clinical science
Priapism refers to a sustained erection that lasts for more than four hours and is not the result of sexual excitation. Based on etiopathogenesis, priapism may be classified as either low-flow or high-flow. Low-flow priapism, which is caused by inadequate venous outflow from the corpus cavernosum, results in painful penile ischemia. Low-flow priapism in adults most commonly arises as an adverse effect from treating erectile dysfunction (e.g., sildenafil), while sickle cell disease is the most common cause in children. High-flow priapism is less common and usually the result of perineal trauma. High-flow priapism is not associated with penile ischemia and is therefore painless. Penile blood gas analysis and doppler ultrasound of the penis allow high-flow priapism to be distinguished from low-flow priapism. Low-flow priapism is an acute urological emergency that must be treated within 12 hours; treatment involves aspiration of blood from the corpus cavernosum and injection of phenylephrine. If priapism does not subside, surgical therapy to decompress the penis is indicated. When treated within 12 hours, complete restoration of erectile function is possible; delayed treatment leads to cavernous fibrosis and irreparable damage with erectile dysfunction. Non‑ischemic priapism usually does not require treatment.
- Priapism can affect individuals of all age groups but two peaks are observed at 5–10 years and 20–50 years. 
- Race: no racial predilection
- Sex: Priapism is almost exclusively a male disease (very rarely clitoral priapism may occur). 
Epidemiological data refers to the US, unless otherwise specified.
One or both of the following tests are used to differentiate high-flow from low-flow priapism: 
- Penile blood gas analysis
- Low-flow priapism: poor arterial influx
- High-flow priapism: high arterial influx and adequate outflow
- Other: complete blood count and differential count, peripheral blood smear