LISS Tests

Principle

By using a low ionic strength saline (LISS) that is iso-osmotic, the rate and extent of the first stage of antigen-antibody reactions (sensitization) is enhanced. LISS has fewer ions which reduces the shielding effect that ions have, e.g., cations will shield negative charges on antigens, and anions will shield positive charges on antibodies, thus preventing the oppositely charged antigen and antibody from coming together. Because complement can bind non-specifically to red cells in a low ionic strength medium, the ionic strength of LISS solutions must be no less than 30 mmol/L (0.03 mol/L).

Advantages

  1. Decreased incubation time of 10-15 min (compared to 30-45 min for saline-based tests).
  2. Increase in sensitivity for most clinically significant antibodies.

Disadvantages

  1. Increased sensitivity for cold, clinically insignificant antibodies.
  2. Non-specific binding of complement if ionic strength is too low.

General Methods

  1. LISS suspension: red cells are suspended in a LISS solution instead of saline.
  2. LISS addition: red cells are suspended in isotonic saline and a LISS solution is added to the tests: 2 drops of patient serum + 1 drop of 2-4% saline-suspended cells + 2 drops of LISS.

Precautions

  1. To avoid problems with cold agglutinins, reagents must be brought to RT before use.
  2. The ratio of serum : cells : LISS must be adhered to rigidly in order to maintain the ionic strength of the mixture. If ionic strength is too high, false negatives can occur, and if it is too low, false positives due to complement binding can occur (if clotted specimens and polyspecific AHG are used for IATs).
  3. Before positive reactions are investigated, tests should be repeated using prewarm technique to prevent cold, clinically insignificant antibodies from reacting.
LISS Tests