An IFE performed on a serum sample showed a narrow dark band in the lanes containing anti-γ and anti-λ. What does this result indicate?

The presence of a narrow dark band in lanes containing anti-γ and anti-λ antibodies during an immunofixation electrophoresis (IFE) indicates a monoclonal population of immunoglobulins, specifically IgGλ. This pattern suggests that there is an increased concentration of a single clone of B cells producing Lambda light chain immunoglobulins of the IgG class.

Monoclonality is typically identified when there is a distinct band in IFE, contrasting with a broader pattern seen in polyclonal responses, which involve multiple clones of B cells producing different types of antibodies. Therefore, the narrow band observed in this test signifies that a specific clone is dominating the immunological landscape of the serum sample, indicative of conditions such as multiple myeloma or certain lymphoproliferative disorders where antibody production is skewed towards a single type of immunoglobulin.

Densitometric quantitation would further confirm the extent of this monoclonal response; however, from the visual result alone, the presence of the narrow band is already strong evidence of monoclonal IgGλ. The other options do not align with the characteristic findings or interpretation of immunofixation electrophoresis results.