What does it mean if your blood is bright red?

Bright red blood is a sign of highly oxygenated blood. Pain, fast pulse rate and rapid respirations are generally the cause. Bright red blood is also a sign that an artery has been severed.

Blood is red because it contains a chromophore (colored compound) called heme. The electronic structure of heme is such that it can reversibly bind certain other molecules, one of which is oxygen. The oxy-heme complex is bright red.

If the blood came from an artery, it was probably already bright red. If it came from a vein, the heme will be a sort of dark purplish-red, but as soon as it hits the oxygen in the atmosphere, it will bind and form the bright red oxy-heme complex, so regardless of where you cut yourself, the blood is going to be bright red.

When you give blood at a blood bank, the blood is drawn from a vein, and flows into a bag which keeps the oxygen out. This blood will be the dark purplish-red color of the deoxygenated heme.