The present invention is directed to methods and devices for amending undiluted and partially diluted urine samples in a manner suitable for performing immunoassays for target analytes, for example NGAL. Generally, the urine sample is treated with reagents including at least one of buffer materials, water soluble proteins, urease, and other interferent mitigants. These reagents control the pH of the urine sample in a manner suitable for immuno-binding reactions and ameliorate interferences, particularly during the detection step.