Oxidative stress levels in semen (ROS test)

Sperm produce small amounts of free oxygen radicals (ROS) that are required for their normal function. It is important that these free radicals are removed as soon as they have performed their function so that their levels remain low. There are antioxidants in the sperm environment that keep the levels low. However, if the balance of ROS production and antioxidant activity is disturbed, high levels of free oxygen radicals will build up, causing oxidative stress. This leads to sperm damage and consequently affects fertility. ROS can be simply measured in a fresh semen sample

What we know about oxidative stress and infertility

  • 25 – 40% of infertile men have high levels of ROS and a reduced antioxidant capacity compared with fertile men
  • ROS can cause poor sperm motility and vitality, poor sperm shape (morphology) and reduced sperm count
  • ROS levels can be high in men with both normal and abnormal semen parameters
  • High ROS levels cause sperm DNA fragmentation
  • High ROS levels are correlated with an increased time to natural pregnancy
  • High ROS levels impair fertilisation, affect blastocyst development and reduce pregnancy rates after IVF.

Causes of Oxidative Stress

  • Infection and pus cells
  • Prostatitis
  • Varicocoele
  • Surgery
  • Undescended testes
  • Chronic disease
  • Certain drugs
  • Cigarette smoking
  • Alcohol
  • Excessive exercise
  • Heat exposure
  • Poor diet
  • Exposure to harmful substances


Increased levels of ROS may be reduced with a change in lifestyle and a diet rich in anti-oxidants, designed to protect against oxidative stress. Randomised placebo controlled studies have shown that anti-oxidant supplements can reduce ROS levels and sperm DNA damage, and improve pregnancy rates. Treatment of infections can also reduce ROS levels. A large randomised study compared men with Chlamydia or Ureaplasma infection with and without antibiotics for 3 months. Those treated showed a significant fall in ROS levels, improved sperm motility and a significant increase in pregnancy rates


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