Blood tests are a routine part of medical care, providing valuable insights into a person’s health. The accuracy of these tests relies heavily on proper sample collection, which includes using the correct blood collection tube for each specific diagnostic procedure. Each tube is designed with particular additives or coatings to ensure the blood sample remains stable and suitable for the intended analysis.
The Correct Tube for PSA Testing
For a Prostate-Specific Antigen (PSA) test, the most commonly used blood collection tube is a serum separator tube (SST), typically identified by a gold or red/gray speckled top. These tubes are designed to yield a serum sample, which is the liquid portion of blood remaining after clotting. Some laboratories may also accept samples collected in a plain red-top tube, which lacks additives but still allows the blood to clot naturally to produce serum.
The interior of these tubes contains a clot activator, which accelerates the clotting process. Additionally, SSTs incorporate a serum separator gel at the bottom. During centrifugation, this gel forms a physical barrier between heavier blood cells and lighter serum, ensuring clean separation and preventing contamination. While green-top (lithium heparin) or lavender/pink-top (EDTA) tubes, which produce plasma, may sometimes be listed as acceptable alternatives, serum tubes remain the preferred choice for PSA analysis.
Why Tube Additives Matter for Lab Tests
Blood collection tubes are color-coded to indicate the specific additives they contain, which are crucial for preparing the blood sample for different types of laboratory tests. These additives either promote clotting to produce serum or prevent clotting to maintain the blood in its liquid state as whole blood or plasma.
Clot activators accelerate clot formation for serum collection. Conversely, anticoagulants like EDTA (ethylenediaminetetraacetic acid), heparin, or sodium citrate are added to tubes to prevent blood from clotting. They prevent clotting by binding to calcium ions or inhibiting thrombin. Other additives, such as sodium fluoride, act as preservatives, preventing the breakdown of substances like glucose in the sample, maintaining stability for accurate testing.
Understanding the PSA Test
The PSA test measures prostate-specific antigen, a protein produced by the prostate gland. The prostate is a small gland in the male reproductive system, located just below the bladder, which contributes fluid to semen. While a low level of PSA is normal, elevated levels can signal various prostate conditions.
The test is used to screen for prostate cancer but cannot definitively diagnose it. High PSA levels may also indicate non-cancerous conditions such as an enlarged prostate (BPH), prostatitis, or urinary tract infections. If PSA levels are elevated, further diagnostic steps, such as a prostate biopsy, are required to determine the cause. Beyond screening, the PSA test also monitors prostate cancer treatment effectiveness and detects potential recurrence after therapy.