Toxicology

Assay Integrity and Storage of Samples

• Assay integrity is maintained through the regular assay of quality control material
• Participation in external quality assurance programmes ensures the proficiency of staff and equipment
• In the event of results being challenged, a secondary referee specimen, with security seals intact, shall be made available for testing with the consent of the donor. 
• All samples are stored in a monitored secure refrigerated area
• Negative samples are stored for 1 month. Positive samples are stored for 3 months. Donor, GP and Clinic samples are stored for 1 month.

Reporting Levels 

Interpretation of Results

A confirmed positive result reveals the presence of a drug in the specimen at or above the “cut-off” level. It gives no information about how or when the drug was taken. It also does not provide an indication of impairment. A positive result may relate to previous drug use with no current physical effects. Positive results are reported as ‘Positive’, while a negative result is reported as ‘Negative’.

Drug Detection Times in Urine

The drug detection time is the time from the last dose of the drug until a negative screening result is obtained using the cut-off levels in the above table. Detection times vary with different drugs and different individuals and according to the amount and frequency of drug taken. It is important to note that whilst a drug may be excreted in the urine for a significant time, it may not reach the threshold required for a positive result. The following table lists the average detection times for a number of drugs.

Requesting Drugs of Abuse Testing

Douglass Hanly Moir Pathology Toxicology Department distributes a combined request and chain-of-custody form. This enables all the client details and the tracking of the specimen to be recorded on the one form. It is important to complete the form fully and correctly. Ensure that the client’s full name, date of birth and date of collection are recorded on the form. Details such as medication which the client may be taking are important in interpreting the results of the urine drug test. It is therefore necessary in interpreting results to be aware of therapeutic drugs which the client may be taking.

Confidentiality

Client confidentiality is of the utmost importance. Strict security surrounds specimens and documentation. Results are released only to the requesting authority or directly to the client after thorough identification. All employees of Sonic Clinical Institute sign a confidentiality agreement when they are employed.

Time Taken for Result

 Depending on time of arrival in the laboratory, samples are processed for screening either the same day or the morning after arrival in the laboratory. Hence negative screening results are available within 24 hours of the specimen arriving in the laboratory. Positive results are available within 48 hours of arrival in the laboratory (confirmation of 1 class). Second and further classes may take longer to analyse.

On Site Urine Testing

 On site testing of urine samples offers a preliminary test result. Specimens are collected as outlined in the preceding sections and tested in individual testing kits usually for the five major classes of drugs. Positive on site screening results must be sent to the laboratory for screening by immunoassay and, if necessary, confirmation by Mass Spectrometry. On site screening provides a rapid method for excluding the presence of drugs but, due to the lack of specificity of on-site kits, it does not provide a dependable positive result. Douglass Hanly Moir Pathology Toxicology Department recommends regular quality control checks on negative results by correlation with the laboratory immunoassay screen.  

The Laboratory Testing Process

The initial test is a screening test which identifies a range of illicit and therapeutic substances. Screening is performed by immunoassay on the Olympus AU2700 using Cedia reagents and methodology. Routine screening involves the testing of the following classes:

• Opiates eg heroin, morphine
• Amphetamine type substances eg. speed, ecstasy
• Cannabis metabolites
• Cocaine metabolites
• Benzodiazepines eg tranquillisers, sedatives

Testing can also be performed for additional drugs, including alcohol, methadone and buprenorphineIf the initial screening test is positive, a second unopened sample aliquotted from the original specimen is tested by a different method for confirmation of the initial result. Confirmation of drug classes detected by Immunoassay is performed by Mass Spectrometry . The presence of each drug or metabolite is tested for at or above a predefined cut-off level (see Reporting Levels Table). These levels are dictated by International Standards for urine drug testing and defined in the AS/NZS 4308:2008 standard. The “cut-off” levels are established because the aim of workplace testing is usually to identify significant residues of the targeted drug, not minute traces. For a result to be “positive”, the amount of the drug detected must be at or above the “cut-off” level. If a drug is detected but the level is below the “cut-off” the result will be negative. The “cut-off” levels for some classes differ for screening and confirmation. This is due to the non-specific nature of the screening assay versus the highly specific nature of the GC/MS confirmation.