A urinalysis, or urine test, is a common diagnostic tool used to screen for or monitor various health conditions, including kidney disease, diabetes, and urinary tract infections. The test involves a visual assessment, a chemical dipstick analysis, and a microscopic examination of the sample. Proper preparation and collection technique are essential for accurate results. These guidelines detail the actions and substances to avoid immediately before your scheduled appointment to prevent false readings or sample rejection.
Actions That Dilute or Concentrate the Sample
Do not consume excessive amounts of water or other fluids in the hours immediately preceding your test, as this can severely dilute the urine sample. The concentration of the urine is measured by its specific gravity and creatinine levels; excessive fluid intake lowers both. This dilution can mask the presence of analytes like glucose, protein, or drug metabolites. A sample with low specific gravity and creatinine may be considered “dilute” and require a re-test, especially in drug screenings.
Conversely, do not present a sample while severely dehydrated, as this concentrates the urine. Highly concentrated urine can increase the number of crystals or cells counted during the microscopic examination, potentially suggesting a pathology where none exists. Also, avoid strenuous exercise in the 24 hours before the test. Intense physical activity can temporarily cause blood or protein (transient proteinuria) to appear in the urine, which may lead to unnecessary follow-up testing.
Medications and Supplements to Discuss with Your Doctor
Do not take any prescription, over-the-counter medication, or supplement without first informing the ordering physician, as many substances can interfere with the test. Non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and naproxen can cause false-positive results for cannabinoids and barbiturates on initial drug screens. Certain antibiotics, including rifampin and some quinolones, can trigger false-positives for opiates.
Common antidepressants, such as selective serotonin reuptake inhibitors (SSRIs), may cause false-positive results for benzodiazepines or LSD. Over-the-counter antihistamines can also interfere, potentially leading to false-positive readings for methadone or phencyclidine (PCP). High doses of B vitamins, particularly riboflavin (B2), should be avoided. Since they are water-soluble, they can be excreted, giving the urine a bright fluorescent yellow or orange hue. Also, avoid consuming foods with poppy seeds, as the trace opiate content can lead to a false-positive result.
Foods and Dyes That Alter Visual Results
Do not consume foods that contain strong natural pigments or artificial dyes in the 24 to 48 hours before your collection, as they can alter the sample’s color and clarity. Eating beets, for instance, can cause the urine to turn reddish or pink due to undigested betalain pigments (beeturia). This visual change can be misinterpreted as hematuria, or blood in the urine, which may indicate a serious health issue.
Similar color alterations can be caused by large amounts of rhubarb or blackberries, which may tint the urine red or dark brown. Ingesting products with heavy artificial food colorings, such as those found in some candies or processed foods, can cause the urine to appear an unusual green or blue. These visual interferences can prompt the lab to perform additional testing or require you to submit a new sample. Excessive amounts of carrots can also lend an orange tint to the urine due to beta-carotene excretion.
Errors During the Collection Process
Follow the “clean catch” midstream technique to prevent sample contamination. The initial step requires thoroughly cleaning the genital area with the provided sterile towelettes to remove bacteria and epithelial cells. These external contaminants can lead to a false-positive result for a urinary tract infection or other issues.
When collecting the sample, do not allow the first stream of urine to enter the cup, as this washes away contaminants from the urethra. Collect only the midstream portion, then remove the cup before the flow stops completely. Do not touch the inside rim or inner surface of the sterile collection cup or its lid, as this introduces bacteria from your hands.
Do not allow external materials to enter the sample, as any of these will invalidate the test:
- Menstrual blood
- Vaginal discharge
- Toilet paper
- Fecal matter
Once collected, do not leave the sample at room temperature for an extended period; it should be transported to the lab within 30 minutes or immediately refrigerated if a delay is unavoidable. Finally, securely seal and accurately label the container with your full name, date of birth, and the time of collection to ensure correct processing.