HLA-B27 is a blood test to look for specific protein found on
the surface of white blood cells. The protein is called human
leukocyte antigen B27 (HLA-B27). Human leukocyte antigens (HLAs)
are proteins that help the body’s immune system tell the
difference between its own cells and foreign, harmful
substances. See also: Histocompatibility antigen test Human
leukocyte antigen B27 How the test is performed Blood is drawn
from a vein, usually from the inside of the elbow or the back of
the hand. The puncture site is cleaned with antiseptic. An
elastic band is placed around the upper arm to apply pressure
and cause the vein to swell with blood. A needle is inserted
into the vein, and the blood is collected in an air-tight vial
or a syringe. During the procedure, the band is removed to
restore circulation. Once the blood has been collected, the
needle is removed, and the puncture site is covered to stop any
bleeding. In infants or young children: The area is cleansed
with antiseptic and punctured with a sharp need