Limit of Detection and Limit of Quantitation

The limit of detection, or LOD, is the lowest level at which an analyte can be reliably detected. The limit of quantitation, or LOQ, is the lowest level at which it can be measured with acceptable performance.

Common approaches

LOD and LOQ may be estimated using:

• signal-to-noise
• standard deviation and slope
• replicate low-level samples
• empirical precision and accuracy

Verification

Calculated values should be verified using samples near the proposed limits.

Method and matrix dependence

Limits depend on:

• sample matrix
• preparation
• detector
• injection amount
• chromatographic separation
• analyte response
• noise
• recovery

LOQ and reporting threshold

The method LOQ should support the intended reporting threshold. A laboratory should not routinely report numerical results below a level shown to be quantitatively reliable.

Frequently asked questions

Is LOD always lower than LOQ?

Yes, because detection requires less performance than quantitation.

Can a peak below LOQ still be mentioned?

It may be reported qualitatively according to the method and procedure.

Is signal-to-noise enough to establish LOQ?

Not always. Precision and accuracy should also be considered.

Can LOQ change after method transfer?

Yes. Receiving-laboratory performance must support the transferred limit.

Key takeaways

LOD addresses reliable detection; LOQ addresses reliable measurement. Both must be tied to the actual method, matrix, and analytical purpose.

References

1. ICH Q2(R2). Validation of Analytical Procedures.
2. ICH Q14. Analytical Procedure Development.
3. FDA. Analytical Procedures and Methods Validation for Drugs and Biologics.

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TSMS Labs educational disclaimer: For laboratory research and educational purposes only. Not for human consumption. This content is not medical, clinical, or regulatory advice.