Prostate Specific Antigen (PSA) Free to Total ratio testing

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Dr Sean Mackay Today I’d like to welcome to the PodMd studio Dr Dixon Woon, Dixon is a urological surgeon. His special interest involves; robotic surgery, urological cancer and benign prostatic enlargement.

Today, we’ll be discussing the topic of PSA Free to Total ratio testing..

Our listeners might like to know that Dixon has done another podcast on The Imperfect art of PSA so if you’d like more context listen to that first. 

Otherwise- Dixon, can you describe for our listeners what free to total PSA ratio testing is? 

Yeah. So, when PSA is produced by the prostate cells, it’s actually bound to a protein. This is similar to the pancreatic enzyme. Most of us are aware of trypsinogen and then when it was released into the gastro intestinal tact intestinal tract, it becomes trypsin. So, the protein bound PSA will be processed and then secreted into the ejaculated duct in the free form, which is called free PSA, is that therefore the total PSA is basically the total free PSA plus the protein bound PSA. 

What is the importance of testing free to total PSA ratio?

As I mentioned in my previous talk, the PSA is an imperfect art. It’s not that specific and it’s not that sensitive. So previously in many other tests has been designed to improve the specificity of PSA testing  In particular, when the PSA is between four and 10. So PSA free to total ratio is one of them. It has been shown to be able to improve the accuracy of PSA testing in detecting prostate cancer. So, we know when the free to total PSA is more than 25% risk of a man having prostate cancer is one in 10. When the free total is less than 10%, half of the men will be diagnosed with prostate cancer. 

Should the GP include a free to total test each time the test for PSA?

I don’t think PSA free to total ratio need to be included in every single PSA testing. But if the PSA is more than three and in your follow up PSA testing, then you should incur include a freedom total PSA. And the reason is that the MRI scan would get funded if you total is abnormal when the PSA is three. 

Right, and when should a GP request a MRI?

Unfortunately, right now, to qualify for the MBS funded MRI scan, patient have to have specific criteria is, and also the request it has to be coming from a urologist or a radiation oncologist. And the specific criteria include: the PSA and also the PSA free to total ratio and also family and patient age. The specific criteria is, are: abnormal, digital rectal examination PSA, or more than three or more than two if they have family history. And also, we have a free to total ratio of less than 25%. 

Thank you for your time here today in the PodMD studio. To sum up for us, could you please identify the three key take home messages from today’s podcast on PSA free to total ratio testing

So, take home message. 

Number one is PSA free to total ratio can improve the accuracy of PSA testing in detecting prostate cancer. 

Secondly, it is one of the criteria that is used for MBS funded MRI scanning.

And thirdly you should consider adding free to total PSA, to patients, PSA testing. If the PSA is more than three 

Dixon, thanks so much for giving us some more information on free to total ratios

Thanks for having me again