Urine, a common bodily waste, often raises questions about its stability once it leaves the body. A frequent query is whether urine “goes bad” if not refrigerated. Understanding its composition and changes helps clarify why proper storage is important.
What Urine Is
Urine is primarily water, containing dissolved waste products and chemicals filtered from the blood by the kidneys. These include urea, electrolytes like chloride, sodium, and potassium, and creatinine.
While sterile within the kidneys and bladder, urine picks up bacteria from the urethra upon exiting the body. Freshly voided urine is therefore not entirely free of microorganisms. This presence of bacteria sets the stage for changes when exposed to external conditions.
How Urine Changes Outside the Body
Unrefrigerated urine undergoes noticeable changes due to bacterial activity and chemical reactions. Bacteria multiply rapidly at room temperature, significantly altering the sample.
Urea, a major component, breaks down into ammonia due to bacterial enzymes. This process causes the strong, pungent ammonia odor in standing urine.
As urea converts to ammonia, the urine’s pH increases, becoming more alkaline. Fresh urine is typically slightly acidic, but unrefrigerated urine often becomes cloudy, hazy, and darkens over time. This is due to bacterial growth and substance precipitation.
Crystals can also form and precipitate, especially as the pH changes. Other chemical constituents, such as glucose and ketones, decrease as bacteria consume them. Bilirubin and urobilinogen may also degrade.
Why Proper Storage Matters for Medical Samples
Urine degradation outside the body significantly impacts medical diagnostic testing. Bacterial proliferation and chemical alterations lead to inaccurate test results, affecting diagnoses and treatment plans.
For UTI analysis, unrefrigerated samples can show rapid bacterial growth, obscuring true causative organisms or overestimating bacterial count. This results in inconclusive or false positive results, hindering identification of correct bacteria and appropriate antibiotic treatment.
Chemical changes also compromise other tests. Bacterial consumption of glucose and ketones can cause falsely low readings, impacting diabetes diagnosis or management. Alterations in pH can affect kidney issue detection or medication effectiveness. General urinalysis also risks false-positive protein and false-negative leukocyte/erythrocyte results if samples are not properly stored.
Best Practices for Urine Collection and Storage
Proper collection and storage are essential for accurate urine tests. Samples for medical analysis should be collected in a clean, sterile, tightly sealed container to prevent external contamination. A mid-stream collection technique, where initial and final urine streams are discarded, minimizes urethral contamination.
Ideally, urine samples should be delivered and tested as soon as possible, preferably within 30 minutes to two hours if kept at room temperature. If immediate testing is not possible, refrigerate the sample at around 4°C (39°F). Refrigeration significantly slows bacterial growth and chemical changes. A refrigerated sample can be stored for up to 24 to 48 hours. For longer-term storage, freezing at -20°C (-4°F) is an option, though usually reserved for specific tests.