Kline GA, et al. - In this investigation, researchers tested the assumption that there would be an inverse link between eGFR and 24 hour urine nor/metanephrine(urine NM-MN) measurements in which case such testing would be considered confounded when renal impairment was present. In addition, they determined the degree to which plasma NM-MN results were affected in connection with mild-to-moderate renal impairment. The entire urine NM-MN database involved 15,505 samples from 13,525 unique patients with a median age of 51.2 years (37.5-63) and 58.3% female, 41.5% male. There was no continuous gradient between subnormal renal function and urine NM-MN measures in patients with mild-to-moderate renal impairment. The hypothesized effect on lowered urine NM-MN was evident when the estimated GFR was < 15 ml/min/m². Measurement of 24-hour NM-MN urine is unlikely to be affected by mild-to-moderate renal impairment and may be used as a valid diagnostic test. CKD-specific reference ranges or an alternative test may be required with more advanced renal impairment.