Which statement about PSA is correct?

The statement regarding free PSA being below 25% and its association with malignant disease is based on clinical studies that have shown a significant correlation between lower percentages of free PSA and the likelihood of prostate cancer. Typically, the total PSA in the blood consists of two forms: free PSA and complexed PSA. The ratio of free to total PSA can be particularly useful in distinguishing between benign conditions and prostate cancer.

In practice, a lower percentage of free PSA (such as below 25%) often indicates a higher probability of malignancy. This is particularly important in patients who have elevated total PSA levels, as it helps guide further diagnostic steps, such as biopsy. This relationship is part of the reasoning behind utilizing free PSA testing as a tool to aid in the decision-making processes for prostate health management.

In contrast to this, statements regarding the other options do not hold true under clinical scrutiny. For instance, complexed PSA in plasma being less than free PSA is not typically how these values are understood or reported. Additionally, while a total PSA below 4 ng/mL can suggest a lower risk of prostate cancer, it does not categorically rule out malignancy, as some cancers can still exist with lower serum PSA levels. Finally, a total PSA above 10