Formulation of immunoassay calibrators in pasteurized albumin can significantly enhance their durability.
Calibrator matrix can have significant effects on the commutability of assay standards and on the maintenance of their integrity. We have observed marked instability in progastrin-releasing peptide (proGRP) assay standards traceable to the bovine serum albumin (BSA) used in matrix formulation. Attempts were made to improve calibrator stability using different albumin pretreatments. Observed analyte recoveries in calibrators prepared with untreated BSA were consistently less than 45% after 1 week of storage at 4 degrees C. Pre-treating the BSA by chromatography on immobilized heparin or benzamidine failed to improve calibrator durability with day 7 recoveries of less than 55%. In marked contrast, calibrators formulated with albumin pasteurized at pH 3.0 displayed remarkable stability. Recoveries of >97% were observed after 4 weeks of storage at either 4 degrees C or room temperature. Even calibrators incubated for 4 weeks at 37 degrees C gave recoveries between 91-106%. This improvement was not seen with BSA pasteurized at neutral pH. Albumin pretreatment is straightforward, easily scalable and dramatically improves calibrator stability. Matrix formulated with acid-pasteurized BSA may prove more generally useful when assays are plagued by poor calibrator durability.
Warren
David J
DJ
Department of Medical Biochemistry at Radiumhospitalet, Oslo University Hospital, Oslo, Norway. david.warren@radiumhospitalet.no
Nordlund
Marianne S
MS
Paus
Elisabeth
E
D002021:Buffers; D002138:Calibration; D002846:Chromatography, Affinity; D005470:Fluorometry / Q000592:standards; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007118:Immunoassay / Q000592:standards*; D010446:Peptide Fragments / Q000032:analysis*; D010447:Peptide Hydrolases / Q000097:blood; D011489:Protein Denaturation; D055550:Protein Stability; D011994:Recombinant Proteins / Q000032:analysis; D015203:Reproducibility of Results; D012710:Serum Albumin, Bovine / Q000032:analysis*; D013696:Temperature; D013997:Time Factors
D002021:Buffers; D010446:Peptide Fragments; D011994:Recombinant Proteins; C087079:pro-gastrin-releasing peptide (31-98); D012710:Serum Albumin, Bovine; D010447:Peptide Hydrolases