Bovine Albumin

The albumin phase is meant to detect IgG antibodies that are too small to cause direct agglutination of red cells suspended in saline. The source of the albumin used in lab tests is cows (bovine). The mechanism of action of the albumin is that it increases the dielectric constant and thus decreases the zeta potential, allowing the red cells to come closer. Being a dipolar molecule, albumin can dissipate energy as it rotates, thereby reducing the thickness of the ionic cloud surrounding each cell. Once the red cells are close enough together, the small IgG molecule can span the distance between the cells and cause agglutination.

The method is as follows: 2 or 4 drops of serum (preferably 4) are incubated at 37°C for 15-60 minutes with 1 drop of 3 - 5% cells and 2 - 3 drops of bovine albumin. The test is read macroscopically for agglutination and hemolysis, and can be read microscopically (if negative). This method is a simple albumin addition method.

Antibodies detected in the albumin phase include IgG Rh antibodies, and any IgM antibody that can react at 37°C. Note that albumin is the poorest method for detection of antibodies because both IgM and IgG antibodies react best in other phases. Although it is meant to detect IgG antibodies, the only IgG antibodies that will react in albumin are usually just Rh antibodies (not Duffy or Kidd antibodies).

The albumin method has few, if any, advantages. One claimed advantage is that some antibodies may only react in albumin, but this is debatable. Its disadvantages include (1) it is a relatively insensitive method for both IgG and IgM antibodies; (2) it adds an expense to the cost of the test, since albumin will have to be purchased; (3) it enhances some clinically insignificant cold antibodies.

Bovine Albumin