The Forensic Genetics Laboratory analyzes biological fluids and tissues such as blood, semen, muscle and bone. The DNA contained in these materials is purified and tested to obtain a DNA profile that may link evidence found at a crime scene to an individual.
Analyses biological fluid and tissue for the presence of DNA
Likewise, non-matching DNA profiles can point investigators away from a particular individual. A DNA profile recovered from two or more crime scenes can indicate the same individual was present at more than one crime scene. In addition, DNA testing can establish parentage and can positively identify human remains.
The Polymerase Chain Reaction, or PCR, is used to prepare large quantities of specific DNA regions from small samples recovered from crime scenes. The laboratory utilizes automated genetic analyzers that subject the DNA to capillary electrophoresis to determine DNA profiles.
The laboratory participates in the FBI Combined DNA Index System, or CODIS, a network of local, state and national DNA databases. CODIS links DNA profiles of evidence from unsolved crimes to DNA profiles from convicted offenders and from DNA profiles of other crimes.
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The Harris County Institute of Forensic Sciences Forensic Toxicology Laboratory is accredited by the ANSI National Accreditation Board, which covers compliance with the American Board of Forensic Toxicology standards.
The Institute’s Forensic Toxicology Laboratory is equipped with advanced instrumentation to perform testing services
The laboratory provides analytical services in medicolegal death investigations (postmortem analysis), driving while intoxicated (DWI) by alcohol and/or drugs, and drug-facilitated sexual assault investigations to support medical examiners, law enforcement agencies, the justice system, and other customers within Harris County.
The Institute’s Forensic Toxicology Laboratory is equipped with advanced instrumentation to perform testing services, and its toxicologists apply this wide variety of instrumental techniques in the course of their casework.
Instrumentation and testing services include:
- Headspace Gas Chromatography – Flame Ionization Detection (Headspace GC/FID) – Detects ethanol and other volatile substances
- Enzyme-Linked Immunosorbent Assay (ELISA) – Screens for common classes of drugs
- Gas Chromatography – Mass Spectrometry (GC/MS), Gas Chromatography Tandem Mass Spectrometry (GC/MS/MS) and Liquid Chromatography Tandem Mass Spectrometry (LC/MS/MS) – Confirms and quantifies drugs and their metabolites
The testing performed in a particular case will depend on the case type, customer request, and/or laboratory protocol. The current scope and sensitivity of screening tests may be found here.
Instructions for Collecting and Submitting Specimens for Toxicological Analysis
For full toxicological analysis, it is recommended that the submitting agency provide the following:
Driving While Intoxicated Cases
- Blood is the preferred sample for DWI cases. Please submit two full vials of blood. Blood should be collected in 10 mL glass gray-topped vials containing 100 mg sodium fluoride and 20 mg potassium oxalate.
- Urine is not recommended for DWI cases. Drug-positive urine results only indicate exposure to drugs and cannot be related to drug impairment.
Drug-Facilitated Sexual Assault Cases
- Blood AND urine should be submitted for drug-facilitated sexual assault cases. Please submit two full vials of blood and at least 50 mL of urine. Blood should be collected in 10 mL glass gray-topped vials containing 100 mg sodium fluoride and 20 mg potassium oxalate. Urine may be collected in a specimen bottle or cup.
Failure to submit the recommended volume of blood or urine may result in incomplete testing.
Each specimen vial, bottle, or cup should be labeled with the following:
- Name of the individual from whom the specimen was collected
- Date and time of collection
Specimen vials, bottles, or cups should be stored inside a leak-proof container, such as a plastic bag. The samples then may be placed inside a paper specimen container, such as a cardboard box or envelope, if desired. It is acceptable to include multiple specimen vials, bottles, or cups in one specimen container if they all pertain to the same case. The specimen container should be sealed with evidence tape and must be labeled with the following:
- Initials of the individual submitting the specimen container – initials must be written across both the tape and the container
- Name of the submitting law enforcement agency
- Case number
To maintain the integrity of the specimen, a chain of custody should be initiated upon collection and the specimen should be refrigerated as soon as possible.
- Submit specimens to the Harris County Institute of Forensic Sciences Evidence Reception located at
1861 Old Spanish Trail, Houston, Texas (Click here for detailed Evidence Submission & Testing instructions).
- A completed submission form must accompany the submission. Do not attach the form to the specimen container.
- Click here to download the submission form, or request a form from the Institute’s Evidence Receiving staff during regular business hours.
DWI Testing Protocol
In suspected DWI cases, blood specimens first undergo alcohol testing. If the blood alcohol concentration (BAC) is greater than or equal to 0.100 g/100 mL, no further testing is performed. If the BAC is less than 0.100 g/100 mL, drug testing is performed. Suspected
DWI cases involving a fatality will be tested for drugs, regardless of the BAC.
Forensic toxicologists are frequently asked to provide extrapolation testimony in driving while intoxicated/driving under the influence (DWI/DUI) and drug-facilitated sexual assault cases. Retrograde extrapolation uses the measured blood alcohol concentration (BAC) to estimate the BAC at an earlier time point, typically the time of driving. Anterograde extrapolation is used to estimate either the number of standard drinks necessary to achieve a particular BAC or the reverse, estimate the BAC after a specified number of drinks.
Attorneys seeking extrapolation testimony can complete the Alcohol Calculation Request form or contact the expert reviewer listed on the Toxicology Report. Specific conditions are required to perform retrograde and anterograde calculations; therefore, calculations may not be possible if necessary information is missing and/or incomplete or if case circumstances are not conducive to extrapolation. Once completed, the written extrapolation opinion will state the basis for the opinion, including any assumptions made, and will be technically reviewed by another expert toxicologist prior to release. Please allow at least one week for the Toxicology Opinion to be emailed to the requestor.
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Accredited by both the ANSI National Accreditation Board (ANAB), and the Texas Forensic Science Commission
In accordance with Texas state statutes, the Institute’s Drug Chemistry Laboratory (DCL) analyzes suspected drug evidence seized by law enforcement agencies in Harris County. Examples include:
- Well known drugs of abuse such as marijuana, cocaine, methamphetamine, heroin, and pharmaceutical preparations
- New and emerging classes of drugs such as synthetic cannabinoids (“KUSH,” “Spice”), synthetic cathinones (“bath salts”), and substituted phenethylamines such as “NBOMes”
- Clandestinely manufactured tablets which mimic pharmaceutical tablets
On average, the DCL completes 7,000 to 10,000 cases each year. Findings are presented in analytical reports used to support the criminal justice system in Harris County.
Instrumentation used in the Drug Chemistry Laboratory includes:
- Gas Chromatograph-Flame Ionization Detector (GC-FID)
- Gas Chromatograph-Mass Spectrometer (GC-MS)
- Gas Chromatograph-Infrared Detector (GC-IRD)
- Direct Analysis in Real Time- Time of Flight (DART-TOF)
- Fourier Transform Infrared Spectrometer (FTIR)
- Ultraviolet/Visible Spectrometer (UV)
- CombiFlash Rf+
- Desktop Nuclear Magnetic Resonance (NMR)
- Stereoscope with a 12.5-megapixel digital camera attachment
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The Trace Evidence Laboratory offers services involving the two forensic sub-disciplines of Gunshot Residue Analysis and Fire Debris Analysis.
Provides gunshot residue and fire debris analysis
Gunshot residue analysis is performed utilizing Scanning Electron Microscopy/Energy Dispersive Spectrometry (SEM/EDS). The micron-sized particles from the discharge of a vast majority of ammunition primers can be identified by the presence of lead, barium, and antimony.
The laboratory also offers the analysis of fire debris samples for the presence of ignitable liquid residues. Samples of debris from suspicious fires are submitted and analyzed by chemists for the presence of gasoline, petroleum distillates, and a wide-ranging variety of other ignitable liquids. The analysis is performed with gas chromatography with mass-selective detection. Two members of the staff are board certified by the American Board of Criminalistics.
All members of the staff are board certified by the American Board of Criminalistics.
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The Firearms Laboratory evaluates fired cartridge casings and bullets recovered from crime scenes, and firearms involved in violent, gun-related incidents. Typically, microscopic markings on recovered cartridge cases and bullets are compared to markings made by a suspect’s firearm, or if no firearm is recovered, then a comparison is made to cartridge cases stored in a database. Often the type and manufacturer of the firearm can be determined by laboratory examination of the cartridge case or bullet in the absence of the firearm.
Evaluates fired cartridge casings and bullets recovered from crime scenes, and firearms involved in violent, gun-related incidents
The Firearms Laboratory participates in the Integrated Ballistics Imaging System (IBIS). IBIS stores and compares images of fired cartridge cases from crime scenes to images of cartridge cases test fired from recovered firearms. Through the use of this technology, the Firearms Laboratory can link recovered firearms to unsolved crimes.
Serial number restoration is another service performed by the Firearms Laboratory. This capability can assist in the identification of a weapon, even when the manufacturer’s serial numbers have been filed off. This can assist investigations in many ways. For example, it may allow a stolen firearm to be returned to its legal owner by using E-Trace, a web based application that allows firearms to be traced via the National Tracing Center of the Bureau of Alcohol, Tobacco, Firearms and Explosives. Firearm tracing can aid investigators in seeking to identify sources of crime guns and ‘straw’ purchases.
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