How to calculate prostate health index

The current clinical formula for calculating the prostate health index (phi) is "free prostate antigen precursor (p2PSA) ÷ free prostate antigen (fPSA)" multiplied by the square root of total prostate antigen (tPSA). You don't have to do the calculations yourself. The laboratory will measure all three indicators and directly calculate the final phi value.

Last week, I met a 48-year-old brother in the outpatient clinic. His annual physical examination tPSA was 4.3ng/ml, just above the commonly mentioned critical value of 4ng/ml. The physical examination institution directly recommended him to have a prostate puncture, which scared him so much that he couldn't sleep well for two nights in a row. Later, he was re-tested for fPSA and p2PSA, and the calculated phi was only 22, which is far lower than the commonly used critical value of 27 in our center. I suggested that he just re-examine in three months, and there was no need to rush for an invasive puncture, which saved a lot of trouble.

Although the formula seems to be just a simple operation of three numbers, in fact, it integrates the advantages of several indicators. If you think about it, the tPSA in a normal physical examination is like a big sieve. It can be elevated by any slight change - eating a spicy hot pot, holding in urine for two hours, or even just a little benign hyperplasia of the prostate can push the value up. Looking at it alone can easily cause a false alarm. fPSA is a relatively "benign" part of PSA. The higher the proportion, the less likely it is to be cancer. p2PSA is the subtype most closely related to cancer. The phi compiled from three numbers is equivalent to filtering out these interference items as much as possible. Especially for people with tPSA in the "gray area" of 4-10ng/ml, the accuracy of using phi to judge whether to need a puncture is almost 30% higher than looking at tPSA alone.

However, there is no completely unified conclusion on the critical value of phi in the industry. Most European and American people use 30 as the cut-off, and further puncture is recommended only if it exceeds 30. However, the prostate volume of our Asian population is generally smaller, and the incidence characteristics of prostate cancer are also different. Many domestic tertiary urology departments The center prefers to set the critical value between 26 and 27. Some studies have also mentioned that the critical value can be appropriately raised for the elderly group over 70 years old to avoid unnecessary excessive punctures. The specific judgment should be based on one's own symptoms and the clinical evaluation of the doctor. Don't just stick to the numerical value.

There is another point that is easily overlooked: the prerequisite for calculating phi is sufficient preparation before blood collection. If you have a digital rectal examination 1-3 days before the test, ride a bicycle for a long time, or have sex, several PSA indicators may rise temporarily, and the calculated results will be inaccurate. I met a 27-year-old boy before who had a tPSA of 6.1 during his physical examination at work. He was so scared that he thought he had cancer. After careful questioning, he found out that he had just ridden a 20-kilometer shared bicycle to play in a country park the day before the examination. He was asked to completely avoid these influencing factors after two weeks before re-examining. All three indicators returned to the normal range, and the phi was only 18, which is completely fine.

Of course, this indicator is not 100% accurate. If you have problems such as difficulty urinating, blood in the urine, or prostate induration during digital rectal examination, even if the phi value is not high, you must follow the doctor's advice for further investigation. Don't wait for a chance.