The serum contains a small amount of hemoglobin, which is related to the number of cell ruptures during blood collection. As long as the content of hemoglobin is within the range prescribed by the Pharmacopoeia, the shade of color has nothing to do with the quality of the serum and does not affect cell culture. National Pharmacopoeia regulations ≤20mg / dL (Note: 1dL = 100 ml), also written as <0.02% (w / v)