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Screening

Most cases of prostate cancer are diagnosed through screening tests, when tumors are too small to cause any symptoms. This is done through blood tests to measure levels of the protein prostate-specific antigen (PSA), which are elevated in those with enlarged prostates, whether due to prostate cancer or benign prostatic hyperplasia. The typical man's blood has around 1 nanogram (ng) of PSA per milliliter (mL) of blood tested. Those with PSA levels below average are very unlikely to develop dangerous prostate cancer over the next 8 to 10 years. Men with PSA levels above 4 ng/mL are at increased risk – around 1 in 4 will develop prostate cancer – and are often referred for a prostate biopsy. PSA levels over 10 ng/mL indicate an even higher risk: over half of men in this group develop prostate cancer. Men with high PSA levels are often recommended to repeat the blood test four to six weeks later, as PSA levels can fluctuate unrelated to prostate cancer. Benign prostatic hyperplasia, prostate infection, recent ejaculation, and some urological procedures can increase PSA levels; taking 5α-reductase inhibitors can decrease PSA levels.

Those with elevated PSA may undergo secondary screening blood tests that measure subtypes of PSA and other molecules to better predict the likelihood that a person will develop aggressive prostate cancer. Many measure "free PSA" – the fraction of PSA unbound to other blood proteins, usually around 10% to 30%. Men who have a lower percentage of free PSA are more likely to have prostate cancer. Several common tests more accurately detect prostate cancer cases by also measuring subtypes of free PSA, including the Prostate Health Index (measures a fragment called −2proPSA) and 4K score (measures intact free PSA). Other tests measure blood levels of additional prostate-related proteins such as kallikrein-2 (also measured by 4K score), or urine levels of mRNA molecules common to prostate tumors like PCA3 and TMPRSS2 fused to ERG.

Several large studies have found that men screened for prostate cancer have a reduced risk of dying from the disease; however, detection of cancer cases that would not have otherwise impacted health can cause anxiety, and lead to unneeded biopsies and treatments, both of which can cause unwanted complications. Major national health organizations offer differing recommendations, attempting to balance the benefits of early diagnosis with the potential harms of treating people whose tumors are unlikely to impact health. Most medical guidelines recommend that men at high risk of prostate cancer (due to age, family history, ethnicity, or prior evidence of high blood PSA levels) be counseled on the risks and benefits of PSA testing, and be offered access to screening tests. Medical guidelines generally recommend against screening for men over age 70, or with a life expectancy of less than 10 years, as a newly diagnosed prostate cancer is unlikely to impact their natural lifespan. Uptake of screening varies by geography – more than 80% of men are screened in the US and Western Europe, 20% of men in Japan, and screening is rare in regions with a low Human Development Index.