Methods and Procedures

10.1 General:

Test methods and procedures used must be accepted in the field or supported by data gathered and recorded in a scientific manner. Since a variety of scientific procedures may validly be applied to a given problem, standards and criteria for assessing procedures need to remain flexible.
In forensic science, well established procedures are often scattered throughout peer-reviewed literature as well as in less formal documents obtained from conference proceedings and in house laboratory manuals. Furthermore, minor modifications to improve published methods can be implemented by a laboratory as appropriate to a particular need.The important point is that the procedures used be demonstrably capable of producing valid results.

Even though a procedure may be widely used, there is often no single document articulating a professional consensus as to its acceptability. Under these circumstances, it relies on the technical knowledge of its members, the inspection team and/or a NABL Committee comprising recognized experts in the field.

The methods must be subjected to a validation study. This may be done internally, externally and/ or collaboratively. Exchange of blind and reference samples with another competent laboratory is particularly useful for detecting any internal systematic error. It should be noted that written documentation for each validation study needs to be maintained for future reference.

The written technical procedures should include descriptions of sample preparation methods,controls, standards, and calibration procedures. They should also include a discussion of precautions, possible sources of error and literature references. Although many acceptable procedures may exist to perform a particular examination, considerable variations; in case samples require that forensic scientists have the flexibility to exercise discretion in selecting the method most appropriate to the problem at hand. The laboratory Director needs to ensure that the procedures used must meet acceptable scientific standards (e.g. the use of positive and negative controls). Additionally, standards and reagents used should be of satisfactory quality, (e.g. labelled of certified purity). 

Examiners in serology must have:

a. Access to well established population data bases on the distribution of all genetic markers which are typed in the laboratory and should have:

b. Access to generate local population data bases on the distribution of all the genetic markers which are typed in the laboratory.

Where sampling is carried out as a part of the test method, documented procedures which include a sampling plan using appropriate statistical techniques must be used. Accreditation cannot be granted for tests/examinations that a laboratory has never performed or for which records of performance are not available. It is accepted, however, that forensic science laboratories are called upon from time to time to undertake analyses/examinations not covered by the scope of their accreditation. In such cases a laboratory may choose from the following options:

a. The laboratory can perform the test/examination and report the result ensuring that no inference can be drawn that accreditation is held for the service.

b. The laboratory can seek accreditation prior to performing the test/examination and reporting the results.

c. The laboratory can perform the test/examination and report the result indicating that accreditation is not held for the service and seek retrospective accreditation for the test/examination.

Retrospective accreditation can only be granted when a laboratory can demonstrate that all accreditation requirements (including method validation/verification, equipment calibration,staff training etc.) were met at the time the test/examination in question was performed.

10.2 Documentation

Test methods and related procedures (e.g. sample procurement) must be documented and readily available to the analysts/examiners. In addition to a description of the steps involved in the analysis/ examination, documentation of methods and procedures must include, where appropriate:

a. Description of the sample/ item to be tested/ examined.

b. Parameters or quantities to be determined.

c. Equipment/ instrumentation required.

d. Description of sample preparation methods, controls, standards and calibration procedures.

e. A discussion of precautions, possible sources of error or limitations of the procedure.

f. Criteria for the rejection of suspect results.

g. Data/ observations to be recorded and method of analysis and presentation.

h. Literature references.

The availability of documented methods will give the examiner the necessary resource material to support written conclusions and expert testimony. 

Where a test can be performed by more than one method, there must be a documented criteria for method selection. Where appropriate, the degree of correlation between the

methods must be established and documented.

10.3 Method Validation

All technical procedures used by a forensic science laboratory must be fully validated before using them for casework. (Validation is the developmental process used to acquire the necessary information to assess the ability of a procedure to obtain a result reliably, to determine the conditions under which such results can be obtained and to determine the limitations of the procedure. The validation process identifies critical aspects of a procedure, which must be carefully controlled and monitored. 

Validation studies can be conducted by the scientific community (as in the case of standard or published methods) or by the forensic science laboratory itself (as in the case of methods developed       in-house or where significant modifications are made to previously validated methods).

Methods may be validated by comparison with other established methods using certified reference materials (where available) or materials of known characteristics. In validating test methods, the following issues (among others) may need to be determined, as appropriate:

• Matrix defects

• Interferences

• Sample homogeneity

• Concentration ranges

• Specificity

• Stability of measured compounds

• Linearity range

• Population distribution

• Precision

Methods developed in-house for both qualitative work must be validated by the laboratory before use. Where a significant modification is made to a validated method, the modification must be appropriately validated by the laboratory before the method is used. Records of all inhouse validations must be maintained for future reference. 

Where a laboratory introduces a new (validated) method, it must first demonstrate the reliability of the procedure in-house against any documented performance characteristics of that procedure. As a minimum, the method must be tested using known samples (e.g. proficiency test samples, samples form an external agency). It is recommended that the method also be tested using non-probative samples. Records of performance verification must be maintained for future reference.

10.4 Reference Materials

Reference materials must be traceable to national and international certified standard reference materials, where possible. Reference materials, certified reference materials and reference collections must be uniquely identified and full details recorded. Purchase, issue and use of these materials must be controlled and records must be maintained.

10.5 Standards and Reagents

The quality of the standard samples and reagents must be adequate for the procedure used. Lot/batch numbers of standards and critical reagents must be recorded. All critical reagents must be routinely tested for their reliability. Standards and reagents must be labelled with:

a. Name of the reagent and standard

b.Concentration, where appropriate

c. Preparation date

d. Identity of the preparer. 

Where necessary, the following must also be included on labels:

- Expiry date

- Storage conditions

- Hazard warning.