The prostate-specific antigen (PSA) test is a common blood screening tool used to assess prostate health, primarily as an indicator for potential prostate cancer. This test measures the level of a protein that is produced almost exclusively by the cells of the prostate gland. Understanding the numerical result requires context, as a single high number does not automatically indicate cancer. For men, age is one of the most important factors in determining what constitutes a normal or expected PSA reading. Interpreting the result correctly depends heavily on knowing how a man’s age influences his baseline PSA level.
Understanding Prostate-Specific Antigen
Prostate-specific antigen is a serine protease, an enzyme whose primary biological function is to liquefy the semen after ejaculation, allowing sperm to move freely. PSA is produced by both the normal epithelial cells lining the prostate ducts and by prostate cancer cells. Small amounts of this protein naturally leak from the gland into the bloodstream, where the PSA test measures its concentration.
The PSA measured in the blood exists in two main forms: bound and free. Bound PSA is attached to other proteins in the bloodstream, while free PSA circulates unattached. The total PSA value reported is the sum of both the bound and free forms. The ratio between the free and total PSA can later provide more specific information to clinicians when the total level is elevated.
Age-Specific PSA Reference Ranges
For many years, a total PSA level of 4.0 nanograms per milliliter (ng/mL) was considered the universal upper limit of normal for all men. This traditional cutoff is now largely considered outdated, especially for older men, because the prostate gland naturally grows throughout a man’s life. As the gland increases in size, it produces more PSA, meaning a higher reading is often expected in later years.
Clinicians now frequently use age-stratified reference ranges to interpret PSA results more accurately. For men in their 60s, the expected upper limit is often around 4.5 ng/mL. For the 70-year-old age group, the acceptable range expands, with many guidelines suggesting an upper limit of approximately 6.5 ng/mL. A PSA value within this range for a 70-year-old is less concerning than the same value would be for a younger man. This age-specific approach helps reduce unnecessary anxiety and follow-up testing for benign age-related prostate enlargement.
Factors That Influence PSA Readings
A PSA reading is not a fixed number and can be temporarily or chronically influenced by several non-cancerous factors, leading to an elevated result. The most common cause of a high PSA in older men is Benign Prostatic Hyperplasia (BPH), a non-cancerous enlargement of the prostate that occurs naturally with age. As the prostate tissue mass increases, so does the amount of PSA produced and released into the bloodstream.
Inflammation or infection of the prostate, known as prostatitis, can also significantly and temporarily raise PSA levels. Similarly, a urinary tract infection can irritate the surrounding prostate tissue, causing a spike in the protein’s release. These inflammatory conditions usually require a period of six weeks after treatment before a reliable PSA test can be performed.
Physical activities or procedures that stimulate the prostate gland can also lead to temporary elevations. Recent ejaculation, vigorous exercise like a long-distance bicycle ride, or medical procedures such as a digital rectal exam (DRE) or the insertion of a catheter can cause a short-term rise in the reading. Certain medications, such as finasteride or dutasteride used to treat BPH, can artificially lower PSA levels and must be accounted for by the doctor.
Interpreting Elevated PSA and Next Steps
When a total PSA reading is elevated above the age-appropriate threshold, doctors often turn to secondary interpretive tools before recommending a biopsy.
PSA Velocity
PSA velocity measures the rate of change in the PSA level over a series of tests, usually taken over an 18 to 24-month period. A rapid increase, defined as greater than 0.75 ng/mL per year, is considered more suspicious than a stable, slightly elevated reading.
Free-to-Total PSA Ratio
The free-to-total PSA ratio is particularly useful when the total PSA falls in the intermediate range of 4 to 10 ng/mL. A lower percentage of free PSA relative to the total suggests a higher likelihood of cancer. A higher percentage points toward a benign condition like BPH. For example, a free PSA percentage above 25% is associated with a lower cancer risk, while a percentage below 10% may increase the concern.
PSA Density
The PSA density is calculated by dividing the total PSA level by the volume of the prostate gland, usually determined through an ultrasound or MRI. Since cancerous tissue typically produces more PSA per unit volume than benign tissue, a PSA density greater than 0.15 ng/mL per cubic centimeter may raise the suspicion of cancer. If these secondary measures still suggest an increased risk, the next step may involve a multiparametric MRI of the prostate to identify suspicious areas, which can then guide a decision regarding a prostate biopsy.