What happens if the second glass in a three-glass collection is positive?

When the second glass in a three-glass collection of urine is positive, it signifies contamination in the sample, which makes the results unreliable. In a three-glass collection, urine is collected in three separate containers to help differentiate between sources of possible infection or pathology. Each glass represents urine from a different part of the urinary tract, specifically aimed at identifying the source of any infection, with the first typically reflecting the urethra, the second the bladder, and the third potentially indicating the prostatic fluid in males.

If the second glass shows a positive result, it raises concerns about whether the sample accurately reflects the bladder's condition or if it has been contaminated by pathogens from the external environment, thus rendering the test results invalid. This invalidation necessitates that the test be carefully scrutinized, as it cannot yield reliable diagnostic value due to the potential influence of external contamination. It highlights the importance of proper collection techniques in urine analysis to ensure the validity of the test results.