Dear AllJust wondering if there are members who can advise on if there are defined standards on how long can PSA blood samples remain within whole blood samples before they reach the end of their shelf life?
I will explain that the NHS in UK have set a standard of a max time of 16 hours between the sample coming out of the arm until it is spun in a centrifuge. If longer then the sample should be taken again. The reason being that over time PSA levels will reduce if the sample remains whole ie unspun.
Notwithstanding the NHS and NICE guidance of 16 hours the lab that is used within our area has decided that it is not convinced that 16 hours is the standard they wish to adhere to and they have selected 24 hours as their cut off point.
I have trawled through various medical papers and it seems to revolve around freePSA being most unstable.
I just wondered if in the US there were standard applied by institutions as to what the max cut off time is permitted for PSA sample testing?
Cheers
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From AI: The maximum amount of time that should be allowed between drawing a blood specimen for prostate-specific antigen (PSA) testing and spinning it down depends on the specific laboratory guidelines and protocols in place. However, in general, it is recommended to process the blood specimen within 2 hours of collection.
PSA is a protein produced by the prostate gland, and its levels in the blood can be used as a marker for prostate health. To ensure accurate and reliable results, it is important to handle the blood specimen properly, including timely processing.
After the blood is drawn, it is typically placed in a tube and allowed to clot. The tube is then centrifuged to separate the serum or plasma from the cellular components. The serum or plasma is then used for PSA testing.
Delaying the processing of the blood specimen beyond the recommended time frame can potentially affect the stability of PSA and lead to inaccurate results. It is therefore important to follow the specific instructions provided by the laboratory conducting the PSA testing and ensure that the blood specimen is processed in a timely manner.
If you have any concerns or questions about the handling and processing of blood specimens for PSA testing, it is recommended to consult with the healthcare professional or laboratory conducting the test. They can provide you with specific guidelines and instructions based on their protocols and ensure that the blood specimen is handled appropriately for accurate PSA measurement.
It is simple maths: PSA half-life is quoted to be 2.5 to 3.5 days. Let's do some number crunching assuming an average half-life of 3 days or 72 hours. The residual PSA after 2 hours is 98%, 86% after 16 hours and finally 79% after 24 hours. I usually have blood drawn at 9:00 to 9:30 in the morning and receive the report by e-mail early in the afternoon. Once, the report came the day after the draw and it was suspiciously lower than anticipated.
Like you I had a PSA sample taken in the morning and it took 32 hours before the serum was separated and hence the result being a test sample result lower than the first.
I only discovered this following me pulling my medical records and asking some questions
As a result started poking around the subject more.
It seems that PSA testing has two elements within a sample:-
1. Free psa
2. " total" PSA or bound PSA
The free psa is psa that may not be fully formed or wrongly formed and can account for 30% of the overall psa in a sample. Free psa is quite unstable in the blood and rapidly drops in level if retained as a whole bllod sample.The bound psa has firmly attached itself to a protein and hence is much more stable than free psa.
It seems that once the sample is spun and the serum separated then the serum sample is much more stable especially if kept at lower temperatures.
I suppose what I am looking for is what are the PSA test regiems looking at. Are they wanting the quickest arm to lab time so as to capture as much psa in the sample as possible or are they happy to accept a 16 hour delay to separate the serum and hence the consequential loss in psa because of drop off with time and hence a lower test result? If that is the case then do Dr's look at the result and add a bit onto the test result to make it comparable to what a test result should have been if it had been spun straight away?
It seems to me that there are many questions surrounding the whole issue of psa testing.
a) For people still having their prostate the higher the free component into the mix, the better.
b) For people post RP a) is reversed to the _lesser_ the free component into the mix, the better.
Yet, this may have to do with PSA free vs total readings (two different assays involved), as if total is low enough free is even lower, hence, difficult to measure. One of the labs I use has a cut-off value for the total PSA bellow which they will not analyze for free PSA. I tried to, but they refused. Don't remember what this value was, but my highest total PSA of 0.17 is definitely deep bellow this.
Dear LowT,Thanks for your input, much appreciated.
Finding the right number following delay it seems to me would be a hard call since I suspect that you would have to have an idea of the free PSA at the outset since its the free psa that drops the most with time.
I suspect that some bright spark could run tests and then come up with some general algorithm based on averages, just for the sake of an example I will make an example up :that for every hour delayed, for the first 16 hours then the drop off rate is 1% per hour???? As I say who knows what the exact drop off rates are per hour.
My view is that it's best to get the sample from the arm and into the lab and spun straight away and hence minimise the drop off in free PSA. Hence that should give you the best indication of the holistic PSA level in the blood. Hence I take myself off to the hospital where they have an in house lab and it's a short time from arm to centrifuge.
Delay in getting it spun seems to produce a lower result and hence I refuse to have a sample taken within the community which then is ferried to a lab miles away and hence creates significant time delay in it being spun and the serum separated.
I suppose, like you, I am very curious if there is some boffin out there on the chat line who can actually disabuse us as to what the clinical facts are. I wonder if TallAllen has seen this post since he seems to be very knowledgeable on all medical matters for PC?
I have tried looking for a definitive recent medical paper on this specific subject but I am struggling to turn up something up that exactly addresses my curiosity.
Prostate-specific antigen (PSA) tests are typically immunoassays, which are biochemical tests that measure the presence or concentration of a substance in a solution through the use of an antibody or an antigen. Immunoassays can be colorimetric, but they can also be chemiluminescent or fluorescent, depending on the specific type of assay used.
Hemolysis, or the breakdown of red blood cells, can potentially affect the results of a PSA test. When red blood cells break down, they release their contents into the surrounding plasma. This can potentially interfere with the assay and lead to inaccurate results.
The extent to which hemolysis affects a PSA test can depend on several factors, including the degree of hemolysis and the specific assay used. If a blood sample is visibly hemolyzed, it may be rejected by the laboratory and a new sample may be required to ensure accurate results.
If you have concerns about a PSA test or its results, it's best to discuss them with your healthcare provider or the laboratory that performed the test. They can provide information that's tailored to your specific situation.
Yes it seems to be all about hemolytic break down within the blood and how this interferes with the result. This hemolytic break down will occur when it remains as a whole blood sample. Hence the reason why the sample is taken from the arm and sent for spinning in the centrifuge to separate the serum. Once the serum is separated then there should be no hemolytic action thereafter.
Gold topped test tubes are often used when psa testing is undertaken and inside the test tube are two substances one to coagulate the blood and the other is a gel which has the function of keeping the coagulated blood and the serum separated once it has been spun. Hence this gel decreases the interaction since it separates the two fractions. Sometimes they will just take the test tube out of the centrifuge and pop it into the fridge until they are ready to remove the serum, since they are confident that the sample of PSA is stable since psa is stable in serum.
Hence, it seems that the best option is to always have the testing done at centres when there is minimal delay between the blood coming out the arm to it being spun and the serum removed for analysis of the PSA levels.
it isn’t just time from draw to lab Bechtel. Here are some additional factors.
“Hemolysis, or the rupture of red blood cells, can occur during or after blood draw due to several reasons:
1. Rough Handling: Vigorous mixing or shaking of the blood sample can cause red blood cells to rupture.
2. Incorrect Needle Size: If the needle used for the blood draw is too small, it can cause mechanical damage to the red blood cells as they pass through the needle.
3. Prolonged Tourniquet Application: If a tourniquet is applied for too long or is too tight, it can cause stasis and congestion in the veins, which can lead to hemolysis.
4. Multiple Attempts: Multiple attempts to draw blood can increase the risk of hemolysis.
5. Incorrect Tube Mixing: After blood is drawn into a tube, it needs to be mixed with the anticoagulant in the tube. If this is done too vigorously, it can cause hemolysis.
6. Forceful Ejection of Blood: If blood is forcefully ejected from the syringe into the collection tube, the impact can cause red blood cells to rupture.
Healthcare professionals are trained to draw blood in a way that minimizes the risk of hemolysis. However, even with the best technique, hemolysis can sometimes occur. If a blood sample is visibly hemolyzed, it may be rejected by the laboratory and a new sample may be required to ensure accurate results.”
However of all the psa blood test I have had then it seems like the nurses are fine with my large prominent veins and they do not have to use a tourniquet. Never had multiple attempts. 1st time every time.
I watch them gently rock the tube for mixing. Never seen a nurse shaking the tube like a spray rattle can.
Never really asked about needle size or shape however it seems as if the sample is in the tube very swiftly so I suspect its not too small a needle otherwise it might take much longer to draw the blood.
So for me it's never seemed to be about how the blood was drawn out of the arm but the process thereafter in how long it takes to get the serum separated which will have the most impact on the result. This is where it would be good if there was an expert in phlebotomy and lab processes could wade in and give us the full nine yards on what the correct clinical interpretation of how time delay of separating the serum actually affect the result?
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