tPSA is also known as total prostate-specific antigen. It is a protein secreted by the prostate gland and is found only within the epithelium of the prostatic tubules. Under normal circumstances, it is isolated from the blood system and PSA is not detected in blood tests, usually at a normal value of 0-4 ng/L. However, if the prostate gland becomes cancerous, its epithelial cells are destroyed. This is when the protein enters the bloodstream and is detected. The higher the level, the more likely it is that you have prostate cancer. The blood contains some free state PSA, called fPSA, which has a negative correlation with the total PSA ratio in prostate cancer. When a patient is suspected of having prostate cancer, if it is between 4 and 10 ng/L, the free PSA to total PSA ratio is used to determine if the patient has prostate cancer. If it is above 10ng/L, a direct prostate puncture biopsy is required to rule out the presence of prostate cancer.