What is the primary reason for performing a midstream urine collection?

The primary reason for performing a midstream urine collection is to avoid initial contamination in the specimen. During urination, the first part of the stream can carry contaminants from the urethra and surrounding areas, which can affect the results of the test. By collecting urine from the midstream, the initial flow that may contain these contaminants is excluded, leading to a cleaner and more accurate sample. This method is particularly important in tests where the presence of bacteria, cells, or other substances may misrepresent the results, such as in urinalysis for infections.

In contrast, while collecting a concentrated sample or ensuring a maximum test volume may seem beneficial, these considerations are secondary to the essential need for minimizing contamination to obtain reliable results. Similarly, including the first and last portions of urine runs counter to the goal of achieving a more accurate and uncontaminated midstream sample.