Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (837 page)

   Prenatal testing of pregnant women.

   In some cases of autoimmune hemolytic anemia, the IAT and the DAT may be positive because some autoantibody attaches to the RBCs and some (excess) antibody may not be bound to red cells and be present in the serum.

   Interpretation

   The IAT is positive in the presence of serum alloantibodies in patients previously transfused and immunized against non-self–red cell antigens.

   Limitations

   The IAT may be unable to detect low titer antibodies.

   A positive IAT requires further investigation to identify more precisely the offending antibody.

CO-OXIMETRY

   Definition

   Co-oximetry refers to the measurement of various forms of hemoglobin by dedicated multiwavelength spectrophotometry. It is a measure of the potential oxygen-carrying capacity of the blood.

   Use

   It usually measures concentrations of oxygenated hemoglobin (oxyHb), deoxygenated hemoglobin (deoxyHb or reduced Hb), COHB, and methemoglobin (MetHb) as a percentage of the total hemoglobin concentration in the blood sample.

   Indications

   History consistent with toxin exposure