TABLE 5.

Suggested evaluation steps for EIA kits and comparison of two different suppliers

Step	Procedure
1. Assess analytical sensitivity or minimum detectable level	Determined from 10 replicates of the standard without any amount of the analyte (zero calibrator) (A). The mean for the 10 replicates of the zero standard is calculated in net p, rates, absorbance, or counts per minute. The mean for the zero standard is plotted on graph paper. The mean duplicate for the standard with the lowest value (B) is also plotted on the graph. A line is drawn between points A and B. Two times the standard deviation for 10 replicates of the zero standard is calculated, and the value is added to the mean for 10 replicates. This number is read off of the graph to give the concentration which, by definition, is the minimum detection limit.
2. Intraassay variability	Determined from mean, SD, and % CV for 10 replicates of at least two plasma samples, one in the normal range and the other in the abnormal (high) range, in the same assay.
3. Interassay variability	Determined from mean, SD, and % CV for runs (at least three different runs) of two plasma samples, one each in the normal range and abnormal high range.
4. Comparison of the assays from different suppliers	Assay 10 or more normal and 10 or more abnormal samples with two or more different EIA kits; calculate the correlation coefficient and P values and perform paired t-test.
5. Establish reference range, median, mean, SD, and 5th and 95th percentiles	For this purpose, assay 30 or more serum and/or plasma samples from a reference population that has age, sex, and ethnic distribution representative of the population affected by disease.