Final answer:
The pH level of urine is the least affected by improper storage due to its broad normal range, making it more stable than other analytes like glucose and proteins.
Step-by-step explanation:
The urine test analyte that is affected the least by improperly storing urine is d. pH. The pH value of urine can vary significantly with diet, for instance, meats tend to lower the pH while citrus fruits, vegetables, and dairy products can raise it. The normal pH range is quite broad, from a low of about 4.5 to a high of around 8.0. Therefore, pH is relatively stable even when urine is not stored properly, compared to other analytes such as glucose, proteins, and urobilinogen, which can be more significantly altered due to bacterial growth or enzymatic activity.