Why are some spots much smaller than others in the analyzing step for ISAC 112 chip?

Why are some spots much smaller than others in the analyzing step for ISAC 112 chip?
Small spots can be due to the individual behavior of an allergen/antibody and especially the behavior when the binding is supposed to take place. The binding procedure and the reagents are optimized and the surface that the allergens are attached to is the same for all. Often there is nothing wrong with these spots but if they fail one of the QC criteria they will have to be approved manually. The following limitations are present in the software and if one or more criteria of them is not fulfilled you will get a red QC warning. <ul> <li>Spotsize must be between 120 and 300 µm</li> <li>Signal Mean / Signal median must be between 0.5 and 3</li> <li>Homogeneity within spot must be 80%</li> <li>Triplicate signal CV must be &lt; 25%</li> <li>Triplicate size CV must be &lt; 25%</li> </ul> <img style="float: left;" src="/FAQ/Allergy/ImmunoCAP%20ISAC/Small%20spots.jpg" alt="" width="150" height="204" />
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As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.