In immunofixation electrophoresis, two discrete bands appear at the same electrophoretic location, one reacted with antihuman IgA (α chain specific) reagent and the other reacted with antihuman λ reagent. This is best described as:

• A. An IgA λ monoclonal protein
• B. An IgA λ polyclonal protein
• C. IgA biclonal proteins
• D. Cross-reactivity

Answer: (C)

In immunofixation electrophoresis, a single monoclonal immunoglobulin is identified by a discrete band that appears in both the heavy-chain (IgA) lane and the corresponding light-chain (λ) lane at the same migrational position. The pattern described—two discrete bands at the same location, one reacting with anti-IgA and the other with anti-λ—reflects the heavy chain of an IgA molecule and its λ light chain from the same monoclonal protein. This is best described as an IgAλ monoclonal protein. Biclonal would imply two separate monoclonal proteins, which would not typically produce a single co-migrating pair in this way; cross-reactivity would not consistently yield this precise, paired pattern.