Serum or plasma concentration of pneumococcal polysaccharide antigen (19A, 23F, 4, 6B, 9N, 14, 18C, 19F, 23F, 33F, 35B, 38, 50)

Why This Test Is Done

Your doctor may order this test if you’ve received the pneumococcal vaccination (PCV13 or PPSV23) and want to check if your body produced enough antibodies to protect against pneumococcal infections. It may also be used in people with weakened immune systems, chronic illnesses, or those at high risk of pneumococcal disease to detect early signs of infection.

What to Expect Before the Test

No special preparation is needed. A blood sample will be drawn from a vein, usually in your arm. The process is quick and typically painless. If you’re on blood-thinning medication or have a history of bleeding issues, let your doctor know before the test.

What the Results Mean

Positive results indicate the presence of pneumococcal antigens in your blood, which may signal an active infection or an immune response to vaccination. Negative results suggest no detectable antigens at this time. Results alone don’t diagnose infection—they’re often used alongside clinical symptoms and other tests.

Common Conditions Monitored

This test is most relevant for people who’ve received pneumococcal vaccines but may not have developed full immunity, those with chronic diseases (e.g., diabetes, COPD), or individuals with immune deficiencies (e.g., HIV, chemotherapy). It’s also used in research or clinical trials studying pneumococcal vaccines.