PSA

PSA is a protein the prostate makes to keep semen fluid. Almost all of it goes the right way, into the semen; a small part leaks into the blood, and that small part is what gets measured. With a healthy prostate that is little. Anything that makes the prostate larger, more irritated or more permeable lets more of it leak into the blood. That last point is the heart of this test, and also its weakness. PSA is specific to the prostate, but not to prostate cancer. A benignly enlarged prostate, which almost every man gets with age, makes more PSA because there is more glandular tissue. An inflammation of the prostate or the bladder pushes the value up for weeks. Even a long bike ride or an ejaculation in the days before the draw lifts it a little. And prostate cancer raises it too, but far from always, and rarely in a way that can be read off the number alone. Your report shows PSA in micrograms per litre, at some labs in nanograms per millilitre, and that is exactly the same number. There is no normal value in the usual sense, no range measured in healthy men. What is on your report is a limit, and it rises with age, because the prostate does too. The limit worked with in the Netherlands is 3 µg/L: below 1 µg/L the value is low, from 1 to 3 µg/L normal, and above that follow-up belongs to it.

Prostate cancer is the most common cancer in men, and usually a slow one. Many men get it with age without ever being troubled by it; a smaller share gets an aggressive form that is very treatable when found early. PSA is the only blood value that says anything about that, and that makes it valuable and awkward at the same time. Valuable, because a rising PSA can be the earliest clue, years before there are symptoms. Awkward, because a raised PSA far more often has a benign cause than cancer, and because it also finds slow tumours that would never do harm. Anyone who tests accepts a chance of needless worry and investigation, in exchange for a chance of finding an aggressive tumour in time. That is a trade-off, and it is why the Netherlands has no population screening for prostate cancer: the choice to test is your own, ideally made in a conversation with your GP, with your age, your family and your own preference on the table. For anyone who tests, most of the information sits not in one number but in the series. A PSA that is stable year after year is more reassuring than one that rises, even if both stay under the limit. And anyone who has a first value measured around fifty has a starting point: a low PSA at that age, under 1 µg/L, makes the chance of a relevant prostate cancer in the years after small, and retesting is only worthwhile after five years. Anyone with a father or brother with prostate cancer, or an inherited predisposition such as BRCA2, starts earlier. Lifestyle, to be honest, is not the lever for this value. A healthy weight, exercise and not smoking are good for your prostate and reduce the chance of an aggressive form, but they barely change your PSA; anyone heavier even measures slightly lower because the protein is diluted in more blood. What you do control is the measurement itself: no cycling, ejaculation or internal examination in the two days before, and no draw during or shortly after a bladder or prostate infection.

A raised PSA usually has a benign explanation, and here they are in order of how often they occur: a benignly enlarged prostate, age itself, an inflammation of the prostate or the bladder, and the days before the draw. After an infection PSA can stay raised for up to 12 weeks, and the right response to one high value is therefore usually: measure again after 12 weeks, rested and without cycling. If the value stays above 3 µg/L, further investigation is the usual route, and there a doctor looks at more than the number: the size of the prostate, the ratio of free to total PSA, the rise over time, and where needed an MRI. A low PSA is the ordinary situation, and the lower the more reassuring: under 1 µg/L the chance of a relevant prostate cancer developing in the coming years is small. One cause of an unexpectedly low PSA you need to know: medicines for an enlarged prostate, finasteride and dutasteride, halve the value after a year of use. Anyone taking them doubles the number in their head and mentions it with the result. Age decides what is ordinary. A PSA of 2.5 µg/L is striking in a man of forty and everyday in a man of seventy, which is why most labs print a limit per age group, rising from about 2 µg/L in young men to 6.5 µg/L in men over seventy. The fixed limit of 3 µg/L the GP works with therefore sits below the lab limit for older men and above it for young men. That is not a contradiction: the limit on your report says what is usual at your age, the GP limit says from where on something happens. Read it as a series, under the same conditions and at the same lab. And weigh what the measurement costs you and what it yields: anyone older than seventy, or who for another reason would not want or be able to undergo treatment, gains little from the number, and is better off not measuring.