Control Band (C Line)
Definition
A second line that captures excess labelled antibody regardless of whether the analyte is present. Its appearance confirms the assay ran correctly. A strip with no control band is invalid.
- Function
- Confirms the immunoassay ran correctly
- Appears
- Regardless of analyte presence
- Failure mode
- No control band means the strip is invalid
Common questions
What should an analyst do if the control band fails to appear?+
Treat the result as invalid regardless of what the test line shows, and repeat the assay with a fresh strip and reagents, since a missing control means the test's validity cannot be confirmed.
How does the control band differ functionally from the test line?+
The test line only develops if the target analyte is present in the sample, whereas the control line captures excess labelled antibody regardless of analyte, so it verifies the reagents flowed and reacted properly.
Related terms
- Anti-Human Haemoglobin Antibody
- A monoclonal antibody raised against epitopes unique to human haemoglobin. Forms the detection and capture antibodies on the lateral-flow strip, conferring specificity...
- Cross-Reactivity
- The capacity of an antibody raised against one analyte to bind structurally related compounds. In RIA, cross-reactivity is the main driver of...
- Lateral-Flow Immunochromatography
- A test format in which a liquid sample flows laterally along a membrane, encounters labelled detection antibodies, and is captured at specific...
- Prozone Effect
- A false-negative serological result caused by antibody excess. When antibody concentration is too high relative to antigen, antibodies saturate individual antigen molecules...
- Test Band (T Line)
- The line on the lateral-flow card that appears when the anti-haemoglobin antibody captures haemoglobin-laden conjugate. Its presence constitutes a positive result.