A new method for haptoglobin phenotyping

Haptoglobin is an acute-phase protein with three major phenotypes: Hp 1-1, Hp 2-1 and Hp 2-2. Studies have shown that functional differences between these phenotypes have important consequences in a number of pathological disorders (e.g, cardiovascular disease, autoimmune disorders, infectious disease), making phenotype determination of potential use in the clinical field. Previous methods for haptoglobin phenotyping have involved electrophoresis (starch, acetate and polyacrylamide gels) with phenotype visualization by peroxidase-sensitive stains that were often carcinogenic. Less hazardous immunoblotting and isoelectric focusing procedures are also available but the methods are lengthy, expensive and often complex. Here, we describe a new method for haptoglobin phenotyping using commercially available agarose gels and a non-carcinogenic stain (3,3',5,5'-tetramethylbenzidine). Our method showed 100% agreement with starch gel electrophoresis and reliably distinguished between commercial haptoglobin phenotype standards and serum samples from patients (n=125). We obtained a sensitivity of 0.4 g/L for all phenotypes and the gels were stable for up to 2 months. This safer and easier to use method may permit increased access to knowledge of haptoglobin phenotype, allowing improved patient management and better tailoring of treatment in a variety of clinical conditions.