○ Learn more about a urine drug test kit.
What is a drug test kit and why are they so useful? Most urine drug test kits produce an instant or rapid result in just a few minutes. Manufacturers describe them as a ‘competitive immunoassay’ in which various drugs of abuse compete for antibody binding sites with the conjugate on the analysis strips.
Urine drug test kits screen for drugs using what is considered “Dry chemistry” The chemicals necessary to detect the presence of drugs are dried onto the antibody pads and analysis strips. See the images below.
Figure 1. above is an analysis strip taken from inside of a urine test kit. Notice the letters ‘THC’? ; This indicates the analysis strip detects Marijuana.
When the concentration of a drug is at or above the screen cut-off level, a drug is present. (figure 2.); This means the antibody binding sites are taken by the target drug present in the urine specimen. As a result, there will be no antibodies left to bond with the conjugate drug-protein on the analysis strip, and so no line will form for that specific drug.
When the concentration of a drug is below the screen cut-off level, no drug is present. (figure 3.) The unbound antibodies (which are bound to colloidal gold dye) will bind to the conjugate drug-protein on the analysis strip in a colorimetric reaction creating a visible line called the TEST LINE. The presence of any colored line, no matter how faint, indicates a negative result for that drug.
○ What are the principles of a urine drug test kit?
Urine drug test devices are based on the principle of competitive reaction between a drug or drug metabolites which may be present in a donor’s sample.
The sample during the test migrates upward and hydrates the analysis strip. The mixture then migrates along the membrane by capillary action to the immobilized drug-protein (or antibody) band on the test region. Figure 2.
When a drug is absent in the sample, the colored antibody will bind specifically to form a visible line in the test region.
When a drug is present in a person’s urine sample, and it migrates along the analysis strip it will compete with the drug-protein for the limited antibody sites, the result is the line on the test region will become less intense with increasing drug concentration until it disappears showing a positive result.
When a sufficient concentration of the drug is present in the sample, it will fill the limited antibody binding sites. This will prevent attachment of the colored antibody to the drug-protein on the test region.
This is what makes the apparent colored line appear or disappear on the testing device. Therefore, the presence of the line on the test region (T) indicates a negative result for that drug and the absence of the test line on the test region indicates a positive result for the drug.
A visible line is also generated by a different antigen or antibody reaction at the control region (C) of the test strip. This line should always appear, regardless of the presence of drugs or metabolites in the urine sample.
A negative urine sample will produce both the test line (T) and the control line (C). A positive urine sample will generate only a control line (C); the (C) line demonstrates that the test was successful.
○ What are the limitations of a urine drug test kit?
- The drug test assay is designed for use with human urine only.
- A positive result with any test only indicates the presence of a drug/metabolite and does not indicate or measure intoxication.
- There is always a possibility that a procedural error or adulteration may interfere with the test and cause false results.
- If adulteration is suspected, the test should be repeated with a new sample.
○ What if I am not able to test a urine sample immediately?
- A specimen may be refrigerated at 2-8°C for up to 2 days or frozen at -20°C for a longer period of time.
- Allow the urine specimen to reach room temperature before testing.
- Allow the urine specimen previously frozen to reach room temperature before testing.
- Handling of urine specimens and all materials should be disposed of as if capable of transmitting infection.
- Gloves should be worn to avoid contact with skin.
○ What precautions should I be aware of when using a urine drug test?
- Urine specimens may be potentially infectious.
- Proper handling and disposal should be established prior to testing.
- Always use a clean fresh container to avoid cross-contamination of urine samples.
- Do not remove the device seal until you are ready to perform the analysis.
- Do not use the expiration date.
- A positive result does not always mean the donor has abused drugs as it may have been prescribed by a doctor.
- Do not store and or expose test kits to temperatures greater than 30°C.
- Do not freeze the testing device.
○ How do I interpret a urine drug analysis?
- The drug test is used to obtain a visual, qualitative result and is intended for screening only.
- The urine analysis assay provides only a preliminary result.
- Allow the urine specimen, and or drug test kit to reach room temperature before testing.
- Clinical consideration and professional judgment must be applied to any drug test result, particularly in evaluating a presumptive positive result (non-negative).
- In order to obtain a confirmed result or confirmation, the urine sample should be sent for further analysis to a laboratory. Gas Chromatography/Mass Spectroscopy (GC/MS) is the preferred confirmation method.
○ This is an example of a negative result:
Colored lines appear in both Control Region (C) and Test Region (T). The line in the control region is the control line, which is used to indicate the test was successful. The line in the test region is the drug result line. The test line may have varying intensity either weaker or stronger in color than that of the control line: This is not an indication of drugs being present. A negative result for a drug indicates that the concentration of that drug in urine is below the cutoff level.
○ This is an example of a positive result:
A colored line appears in the control region but no line appears in the test region. The complete absence of a test line indicates a positive result for that drug. A preliminary positive result for a drug indicates that the concentration of that drug in urine is at or above the cutoff level set by SAMHSA.
○ This is an example of an invalid result:
No colored line appears in the control region; If the control line does not form, the test result is inconclusive, repeat the test should with a new test kit.
○ How do I know I tested successfully?
- Manufactures include a built-in procedural control line for each test device. This line will form in the Control band region regardless of the presence or absence of drugs or metabolites.
- The presence of the line in the Control region (C) indicates that the proper sample volume was collected and that the reagents migrated adequately.
- If the line in the Control region (C) does not form, the test is considered invalid.
- It is essential to make sure that the control values are within established limits; i.e., control lines are present otherwise the test results are invalid.
- Sens suspect samples to a SAMHSA approved laboratory for confirmation.
○ What are adulterants?
Adulteration of urine samples may cause erroneous results when drug testing by either interference or by destroying the drug evidence in the urine. Dilution of urine with water is probably the most common adulteration method. Bleach, vinegar, Visine, sodium bicarbonate, sodium nitrite, Drano, soft drinks and hydrogen peroxide are examples of compounds used to adulterate a urine sample. It is vital to ensure the integrity of a urine sample in every drug test.
○ What is a Specimen Validity or Adulterant Check?
Manufacturers have based their tests on the color response of chemical indicators that detect the presence of adulterants. The administrator would use this check to determine its integrity prior to testing.
- Creatinine reacts with a creatinine indicator to form a purplish-brown color complex. The color intensity is directly proportional to the concentration of creatinine which is a waste by-product produced by the body. Urine samples with creatinine concentrations of less than 20 mg/mL are dilute, which may be an indication of contamination.
- Nitrites react to form a pink-red/purple color complex. Urine samples containing nitrate at levels higher than 15 mg/dL are considered adulterated.
- Testing the pH value of the urine sample is based on a color change in the indicator. The standard urine pH ranges from 4 to 9. Urine pH below 4 or above 9 indicates contamination of the specimen with acids or alkalines.
- Bleach or other oxidizing agents react with an oxidant indicator to form a blue-green, brown, or orange color which indicates adulteration with bleach or other oxidizing agents.
- Specific Gravity testing relies on the pKa change of certain pretreated polyelectrolytes about the ionic concentration. The indicator will show color changes from dark blue to blue-green in the urine of low ionic strength to green and yellow-green in the urine of higher ionic concentration. Specific gravity below 1.005 or above 1.025 is considered abnormal, which may indicate adulteration.
An administrator testing for adulterants would compare the color of each test pad with the color block on the Adulteration Color Comparison Chart. Diluted urine samples will produce abnormal colors. An unadulterated urine sample will produce standard colors.
○ Additional information.
Product information on Drug Adulteration Check Strips.
You may find it useful to read our instructions on how to use a urine drug test kit.
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