In quantitative polymerase chain reaction (qPCR), the Limit of Detection (LOD) is the lowest amount of target nucleic acid that can be reliably detected and distinguished from background noise. It quantifies assay sensitivity and is typically expressed as a concentration value (e.g., copies per milliliter).
What Does "Below the Limit of Detection" Mean?
When a qPCR result is reported as "below the limit of detection," it indicates that the target nucleic acid was not detected at a level above the established LOD. This could be due to one of the following reasons:
- The target is present at a concentration below the LOD.
- The presence of inhibitors in the sample prevents detection.
Determining the LOD
The LOD is established by running a series of target dilutions and identifying the point where reliable detection becomes challenging. Several factors influence the specific LOD for an assay, including: sample volume, sample quality, and presence of inhibitors
Interpreting qPCR Results
If your qPCR result falls below the LOD, it means the target is present at a concentration that the assay cannot reliably detect. However, if the result is within the LOD range, the target is present at a detectable concentration. This is typically indicated by a cycle threshold (Ct) value within the LOD range. The Ct value represents the PCR cycle at which the fluorescence signal of the target crosses a certain threshold. A lower Ct value indicates a higher concentration of the target nucleic acid.
Next Steps
Review Data Sheets: To learn more about LuminUltra's Limit of Detection for each qPCR assay, review the GeneCount Assay Data Sheets