Normal serum is useful for reducing background or as a negative control in immunoassays. Pre-incubation of immunoblots or tissue sections in buffer with 1-10% normal serum of the same species as the conjugated antibody host can reduce background due to nonspecific binding of the conjugate, and is sometimes more effective than albumin alone. In indirect immunoassays up to 1% normal serum of the same species as the blotted protein or tissue section can be added to the secondary antibody conjugates to reduce background due to cross-reactivity. Normal serum can be used in assays as a negative control to measure background staining due to nonspecific binding or cross-reactivity, substituting for pre-immune serum if that is not available.
Normal sera from animal species commonly used in antibody production are tested for protein concentration by Biuret and assayed for a normal protein profile by immunoelectrophoresis. They contain 0.01% thimerosal as a preservative.
Store normal sera at -20 °C in working aliquots to avoid freeze-thaw cycles. See the table of normal serum immunoglobulin ranges.