Abstract
The fluorescence polarization immunoassay (FPIA) for measuring serum digoxin levels provides many advantages such as reagent stability and shorter analysis time when compared with other methods. However, the method gives lower digoxin value. This discrepancy may be due to the difference of protein concentration between the digoxin calibrator and patient's serum. We have studied the effect of protein concentration on digoxin level in assaying specimen by the FPIA. It was found that as protein concentration is reduced, digoxin level is increased. The measured digoxin level was particularly higher in solutions when protein concentration was below 5g/dl.
The interference caused by the presence of protein in the dogixin measurement was suppressed by diluting sample with normal saline. The dilution rate was determined in the effort for minimizing the protein concentration difference between the digoxin calibrator and patient's serum. Serum samples of 80 patients were examined for digoxin level by the conventional method and the dilution method of FPIA, as well as by EIA and RIA. The digoxin levels measured by the FPIA dilution method were 20.1% higher on average than those by the FPIA conventional method. Results of the FPIA dilution method correlated well with those of EIA and RIA.
Thus patient's serum with a normal protein range always showed low digoxin levels in the measurement by the FPIA conventional method. We conclude that the FPIA solution method gives relatively accurate results.
