Manual Peak Re-Integration in Forensic Toxicology

Quick answer: Manual peak re-integration can be scientifically defensible in forensic toxicology when the software’s original boundaries do not reasonably capture the validated chromatographic peak, but the change should be governed by documented criteria, applied consistently, preserved in the data record, and reviewed with the rest of the analytical batch. Re-integration is not a substitute for acceptable chromatography, identification criteria, calibration, quality control, or method validation.

What is manual peak re-integration?

Chromatography software normally applies a processing method that identifies peaks and assigns start and stop points for calculating peak area or height. Manual re-integration occurs when an analyst changes those boundaries or otherwise modifies the software’s original integration.

The change may be reasonable when a validated peak is visibly truncated, an algorithm captures excessive baseline, a shoulder is incorrectly included, or an otherwise acceptable peak is processed differently from comparable calibrators and controls. The fact that a peak was manually changed does not establish error or misconduct. The forensic issue is whether the change can be reconstructed and justified under the laboratory’s written procedure.

Why integration can affect a reported concentration

Quantitative LC-MS/MS and GC-MS methods commonly convert an instrumental response into concentration through a calibration model. If the response is based on peak area or an analyte-to-internal-standard area ratio, changing an integration boundary changes the number that enters the calibration equation.

The effect is often small for a large, symmetrical, well-resolved peak. It can be more important when the signal is near the reporting limit, the baseline is unstable, there is a neighboring peak, the chromatogram contains interference, or the analyte and internal-standard peaks are not behaving comparably.

When is manual re-integration scientifically defensible?

A strong laboratory practice does not rely on an analyst’s unstructured visual preference. The decision should be tied to a procedure that tells reviewers what constitutes an acceptable peak and when manual changes are permitted. Relevant considerations may include:

• whether the peak has the expected retention time;
• whether the quantifier and qualifier traces or spectra support the intended analyte;
• whether the peak is sufficiently resolved from neighboring signals;
• whether baseline placement is consistent with comparable samples;
• whether the internal standard behaves normally;
• whether calibrators and controls were processed under the same rules;
• whether the change remains within the validated method and reporting range.

ANSI/ASB Standard 036 provides the validation framework for demonstrating that forensic toxicology methods are fit for their intended use. ANSI/ASB Standard 152 addresses the minimum content expected in forensic toxicology analytical procedures. Together, they reinforce the importance of connecting data processing to a validated method and a sufficiently detailed laboratory procedure.

What should an audit trail preserve?

An audit trail is most useful when it allows a reviewer to reconstruct what changed. Depending on the laboratory information system and instrument software, useful records may include the original integration, the revised integration, the user who made the change, date and time, processing-method version, and any recorded reason or comment.

Not every legacy data system stores every one of those elements. The absence of a particular field does not prove the result is unreliable. But the less reconstructable the processing history is, the more difficult it becomes to determine whether re-integration was consistent, selective, or outcome-driven.

Consistency across the batch matters

A case-sample chromatogram should be reviewed alongside calibrators, controls, blanks, internal standards, and other relevant samples from the run. A question worth asking is whether the same type of peak received the same treatment throughout the batch.

For example, if an analyst manually excludes a shoulder from the case sample but includes an analogous shoulder in calibrators, that difference deserves explanation. Conversely, a documented re-integration rule applied consistently across samples may improve rather than weaken the reliability of the processed data.

For the broader batch framework, see Failed Quality Control in Forensic Toxicology: Batch Review and Technical and Administrative Review in Forensic Toxicology.

Re-integration is not an identification criterion

A well-drawn integration boundary does not establish compound identity. In mass-spectrometric methods, identity may depend on retention time, precursor/product-ion relationships, ion ratios, spectral agreement, and interference controls established during validation. A peak can be integrated cleanly and still fail the laboratory’s identification criteria.

Review integration together with the method’s identity rules. See LC-MS/MS Identification Criteria in Forensic Toxicology.

Low-level results deserve closer scrutiny

At low concentrations, small changes in the included area can represent a larger fraction of the total response. That does not make every low-level result unreliable, but it increases the importance of checking baseline quality, signal-to-noise behavior, interference, calibration performance, and reporting-limit validation.

A laboratory should not use manual integration to create apparent precision that its method has not demonstrated. Results near the lower end of the range remain constrained by the validated method and the laboratory’s reporting policy. See Reporting Limits in Forensic Toxicology: LOD, LOQ & Low-Level Results.

Internal standards can expose processing problems

Internal-standard chromatograms should be reviewed with the analyte. Unusual internal-standard peak shape, area, retention behavior, or integration can indicate extraction problems, injection variability, matrix effects, or data-processing issues. An isotope-labeled internal standard is valuable, but it does not automatically correct every integration or interference problem. See Stable-Isotope Internal Standards in Forensic LC-MS/MS.

Case-review checklist for a manually re-integrated result

• Obtain the original and final chromatograms.
• Identify which trace or transition was manually changed.
• Compare the original and revised peak areas or area ratios.
• Review the corresponding internal-standard peak.
• Compare integration of calibrators, controls, blanks, and neighboring case samples.
• Determine whether the laboratory has written integration/re-integration criteria.
• Review the processing method or integration parameters used for the batch.
• Check whether the data system records the user, date, time, and reason for the change.
• Confirm that retention-time and other identification criteria still pass independently.
• Determine whether the concentration remains within the validated calibration and reporting range.

What does a manual re-integration prove?

By itself, very little. A manual change is neither proof that the laboratory manipulated the result nor proof that the final value is correct. Its significance depends on the reason for the change, the laboratory’s procedure, the raw chromatographic data, the consistency of treatment across the batch, the validation record, and the magnitude of the effect on the reported result.

Professional guidance

A 2025 Journal of Analytical Toxicology review of professional best practices describes analytical data review as a critical quality-assurance function and specifically identifies chromatographic peak shape, resolution, retention time, internal-standard response, and identification criteria as matters for review. ANSI/ASB Standard 054 establishes minimum quality-control practices and requirements for review and monitoring of QC data.

Bottom line: the scientifically important question is not simply whether a peak was manually re-integrated. It is whether the final integration is reproducible, procedurally justified, traceable, consistent with comparable samples, and supported by the validated analytical method.

Last reviewed: September 23, 2026.