Urine, a liquid byproduct of the body, primarily consists of water, with urea and various salts. While urine does not “spoil” in the same way food does, it undergoes notable changes once it leaves the body and is exposed to the environment. These alterations are a natural consequence of its chemical composition and the presence of microorganisms.
The Transformation of Stored Urine
When urine is no longer contained within the body, its constituents begin to change, leading to decomposition and chemical alteration, particularly when kept at room temperature. Clarity decreases as solutes may crystallize. The pH of the urine also tends to rise, becoming more alkaline. Additionally, some of the components within the urine can degrade.
The Agents of Change
These changes in stored urine are primarily driven by two factors: bacterial action and other chemical reactions. Bacteria, which are naturally present in the urethra, can be introduced into the urine upon collection, and urine serves as a favorable growth medium. Many bacteria produce an enzyme called urease, which breaks down the urea in urine into ammonia. This conversion of urea to ammonia leads to an increase in the urine’s pH, making it more alkaline. Other chemical processes also occur, such as the oxidation of urobilinogen to urobilin, which contributes to a darkening of the urine’s color.
Identifying Altered Urine
The transformation of urine outside the body can be observed through several sensory changes. A strong ammonia odor develops, resulting from bacteria breaking down urea into ammonia. The color of urine also darkens over time due to the oxidation of urobilinogen. Urine that has been left standing often becomes hazy or cloudy. This change in clarity is caused by both the multiplication of bacteria and the precipitation of various materials or salts.
Practical Considerations for Urine
The changes in urine outside the body have important implications, particularly for medical diagnostic testing. Prompt examination is necessary for accurate results. Ideally, a urine sample should be tested within 30 minutes to two hours of collection to ensure its integrity. If immediate testing is not possible, refrigeration can slow down these changes, allowing samples to be stored for up to 24 hours. Delays in processing can lead to inaccurate test results, including false positives or negatives for certain indicators, and the degradation of cells and casts within the sample.