A field test is generally a preliminary screen; a laboratory analysis is a later, more detailed examination. They serve different purposes, and the meaning of any result depends on the specific method, sample, and records. An arrest or charging decision can occur before a lab report is complete. That fact alone does not establish that the case must be dismissed or that evidence is inadmissible.

California POST training describes field kits as preliminary and directs forensic laboratory confirmation for evidentiary use. That training material is guidance, not a statute imposing one testing method in every prosecution. Federal NIJ materials also describe multiple field technologies, each with different strengths and limits. California POST, LD 30; NIJ field-device study.

What a field result may show

An officer may use a presumptive test on a suspected substance during an investigation. Depending on the method and circumstances, a result may contribute to an assessment of probable cause before laboratory analysis. A presumptive result is an investigative indication; it should not be described as a definitive identification without reviewing the particular test and its limits.

There is no single “field test.” Technologies vary. The NIJ review discusses different devices and potential limits, including effects from mixtures, maintenance, and operating conditions. A result should therefore be evaluated in context rather than translated into a universal claim about accuracy or error rates.

What to compare in the laboratory record

If a lab report later identifies a substance, counsel can compare the result with the filed charge and earlier records. Useful questions include:

  • Does the report identify the same substance and classification alleged in the charge?
  • Do the package, evidence, and sample identifiers match across the field worksheet, booking or evidence log, lab submission, and report?
  • What method did the laboratory use, and does the report describe a conclusive, inconclusive, or qualified finding?
  • Is the report addressing the tested sample, and do the records document how it was collected, packaged, transferred, and tested?
  • Are there notes about controls, instrument maintenance, mixtures, or limitations relevant to this particular procedure?

These are review questions, not assumptions that a discrepancy exists. A mismatch may call for explanation; a matching identifier does not, by itself, resolve every issue about the sample or method.

Charging and proof are different stages

An NIJ case-processing study found that charging decisions in observed jurisdictions sometimes preceded laboratory confirmation. Because it is a multi-jurisdiction study, it does not establish a California rule. It does illustrate why the presence or absence of a lab report at the time of arrest should be separated from what evidence is eventually presented and whether it proves the charged offense. NIJ controlled-substances case-processing study.

California Health and Safety Code section 11350 is one example of a controlled-substance possession statute. Its text identifies substances and exceptions but does not prescribe a particular forensic instrument. The exact charge matters; do not assume this statute or any specific testing claim applies to every case. Health & Safety Code § 11350.

A lawyer can line up the charging document, field-test record, evidence identifiers, lab report, and handling history to identify questions specific to the case. The Law Offices of David S. Chesley handles California drug charges; to discuss a specific allegation, call (800) 755-5174.