Urine drug testing is common and often conducted for two primary reasons:
- Ensuring workplace safety.
- Designing an informed regimen for the patient.
However, some donors may try to mask their urine sample by adding substances like household chemicals, oxidants, detoxifiers, etc., during drug testing because positive test results have occupational and legal consequences.
Such masking attempts make it harder for clinical physicians to monitor patients’ medication compliance, detect drug abuse and prescription medication diversion. For a workplace supervisor, they get in the way of ensuring workplace safety.
Specimen validity testing (SVT) is employed to validate the integrity of a urine drug test result. It digs deeper into the urine test results and ensures that the urine sample was that of a human without any tampering.
Specimen Validity Testing can check for the following in the urine specimen:
- pH
- Creatinine
- Specific Gravity
- Oxidizing adulterant
- Nitrites
- Glutaraldehyde
- Pyndinium Chlorochromate
Adulterants
Oxidizing adulterant
Donors use chemicals like bleach, chromium (VI), iodine, nitrite, etc., as oxidizing adulterants to interfere with the drugs and drug metabolites in the sample, preventing their detection. Such chemicals also affect the reagents involved in drug testing.
Nitrites
Although nitrites are not a normal component of urine, nitrite levels of up to 3.6 mg/dL may be found in some urine specimens due to urinary tract infections, bacterial contamination or improper storage. Nitrite levels >50 mg/dL are abnormal and are generally considered adulterated by most guidelines.
Glutaraldehyde
Glutaraldehyde is not present in human urine naturally and its detection in a sample is an indication that the urine may have been adulterated as many commercially available urine adulterants contain glutaraldehyde. However, it is notable that in ketoacidosis, starvation or other metabolic abnormalities, ketone bodies may appear in urine and interact with the glutaraldehyde pad to procude atypical colours.
Pyridinium Chlorochromate
The presence of pyridinium chlorochromate in the urine is an indicator of adulteration as it is not a normal constituent of urine. When you are using an SVT strip the formation of a blue or light turquoise gray colour may also indicate the presence of other oxidants.
Dilution, Substitution, and Adulteration
Besides looking for the above mentioned adulterants a Specimen Validity Test will also look at three basic parameters for urine to confirm they are valid, Specific Gravity, Creatinine levels and the pH value. These three values will indicate whether or not the urine is normal human urine.
Creatinine
Creatinine is a normal excretion that ends up in our urine, it comes from the metabolic work of our muscles, and is fairly consistent for all humans. General guidelines state that urine specimens with creatinine levels of less than 20 mg/dL indicate dilution. Although these ranges can be affected by age, sex, diet, muscle mass etc., a sample with a creatinine level <20 mg/dL should be considered dilute. Creatinine concentrations outside of the normal range indicate excessive fluid intake, renal failure, or several other medical conditions.
Specific Gravity
Specific gravity determines the mass of a material in relation to water density. The specific gravity of urine is an indicator of dissolved particle concentration. The specific gravity of normal urine may range from 1.001 to 1.035, however, it is most commonly between 1.016 and 1.022 in adults with normal fluid intake. However, high protein concentration in the urine may elevate the specific gravity value. Low Specific Gravity values may be due to excessive fluid intake, renal failure, diabetes, and other medical conditions. High Specific Gravity values could indicate dehydration, renal dysfunction, and other physiological factors. General guidelines state that specific gravity should be evaluated in conjunction with clinical observation and creatinine levels, as shown in the chart below.
| Creatinine | Specific Gravity | |
| Indicates substitution | ≥2 and < 5 mg/dL | > 1.0010 and < 1.0030 |
| Dilute specimen | ≥ 5 and < 20 mg/dL | > 1.0010 and < 1.0030 |
Drinking large amounts of water, a medical condition or medication, or adding water/liquid to a sample can result in a diluted specimen, making it hard to detect the drugs present in the urine. Lemonade, soft drinks, and sports drinks can be substituted for urine, rendering the result invalid.
pH
The pH level determines whether the urine sample is acidic or basic. Normal urine pH is slightly acidic, but HHS sets the program cut-offs with a pH of about 4.5 to 9. Extremely alkaline (pH > 7.0) or acidic urine (pH < 7.0) is suggestive of sample tampering or adulteration.0.
Adulterated Specimen – pH of < 3.0 or > 11.0
Adding acid, ammonia, lye, vinegar, etc., to the urine sample affects the urine pH and interferes with the initial screening test.