Urine specimens should be analyzed as soon as possible after collection. If urine specimens are allowed to stand at room temperature for an excessive amount of time, the urine pH will become alkaline because of bacterial decomposition of

• A. Protein
• B. Urea
• C. Creatinine
• D. Ketones

Answer: (B)

Urine pH rises when urine is allowed to stand because bacteria that produce urease break down urea into ammonia and carbon dioxide. The ammonia released is alkaline, so it shifts the urine toward a higher, more basic pH. Fresh urine is typically slightly acidic, but bacterial activity in a standing sample can rapidly raise the pH through ureolysis of urea. Other substances like protein, creatinine, or ketones don’t produce this same ammonia-driven alkalinization, so the key change comes from urea being decomposed by bacteria. This is why prompt analysis or refrigeration is recommended to preserve the original pH.