red
Most likely its lavender top tube, EDTA anticoagulant. Please review chemistry or phlebotomy manual about BNP test in your laboratory. It may be different.
Each test has a specific color tube.
EDTA tube or lavender tube
what color tube to draw HepB titer blood test
tiger
Purple tube.
Gray tube
It depends on the test - each test has a different type of test tube top.
A test tube with a red top is used for hcg testing.
SST tube (yellow color)
red