What is a urine drug test kit?
What is a drug test kit and why are they so useful? Most urine drug test kits produces 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 bonding sites with conjugate drugs on the drug screen test 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 test strips. See images below.
The figure 1. above is a test strip taken from inside of a urine drug test kit. Notice the letters ‘THC’? This indicates the test is for testing for Marijuana.
When the concentration of a drug is at or above the drug screen cut-off level, a drug is present. (figure 2.) The antibody bonding sites will all be 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 test strip and so no line will form for that specific drug.
When the concentration of a drug is below the drug 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 test 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 test 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 the sample, it will compete with drug-protein for the limited antibody sites. The line on the test region will become less intense with increasing drug concentration.
When a sufficient concentration of 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 red colored lines appear on the testing device. Therefore, the presence of the line on the test region (T) indicates a negative result for the 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 test line (T) and control line (C), and a positive urine sample will generate only a control line (C). This built-in control 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 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 open test device seal until you are ready to perform the test.
- Do not use the test kit after the expiration date.
- A positive test 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 test?
- The drug test is used to obtain a visual, qualitative result and is intended for screening only.
- A urine drug test assay provides only 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.
Negative result from a urine drug test kit:
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.
Positive result from a urine drug test kit:
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.
Invalid result from a urine drug test kit:
No colored line appears in the control region. If the control line does not form, the test result is inconclusive and the test should be repeated with a new test kit.
What is quality control?
- Manufactures include a built-in procedural control line to 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 has been used and that the reagents migrated properly.
- If the line in the Control region (C) does not form, the test is considered invalid.
- It is important to make sure that the control values are within established limits. If the values of external control do not fall within established limits, the test results are invalid.
- Confirmations should be sent to a SAMHSA approved laboratory.
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 the examples of compounds used to adulterate a urine sample. It is important to ensure the integrity of a urine sample in every drug test.
What is a Specimen Validity or Adulterant Test?
Manufacturers have based this test on the color response of chemical indicators which detect the presence of adulterants. The administrator would use this test 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 adulteration.
- Nitrites react to form a pink-red/purple color complex. Urine samples containing nitrite at levels greater than 15 mg/dl are considered adulterated.
- Testing the pH value of urine sample is based on color change in the indicator. The normal urine pH ranges from 4 to 9. Urine pH below 4 or above 9 indicates adulteration 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 is based on the pKa change of certain pretreated polyelectrolytes in relation to the ionic concentration. The indicator will show color changes from dark blue to blue-green in urine of low ionic concentration to green and yellow green in 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. Adulterated urine samples will produce abnormal colors. Unadulterated urine sample will produce normal colors.
Product information on Drug Adulteration Test Strips.
You may find it useful to read our instructions on how to use a urine drug test kit.