Albuminuria Prevalence in First Morning Void Compared with Previous Random Urine from Adults in the National Health and Nutrition Examination Survey, 2009–2010

BACKGROUND: Albuminuria, defined as urine albumin/creatinine ratio (ACR) ≥30 mg/g, is a diagnostic component of chronic kidney disease (CKD). National estimates of ACR and CKD prevalence have been based on single random urine samples. Although 2 urine samples or a first morning void are known to produce different estimates of ACR, the impact of differing urine sampling schemes on nationally estimated rates of CKD is unknown. METHODS: In 2009-2010, the National Health and Nutrition Examination Survey (NHANES) participants provided 2 untimed urine samples for sequential ACR measurement: an initial random urine collected in the NHANES mobile examination center and a subsequent first morning void collected at home. Rates of albuminuria were calculated in the overall population and broken down by demographics, diagnosed diabetes and hypertension status, and estimated glomerular filtration rate (eGFR). RESULTS: Overall, 43.5% of adults with increased ACR (≥30 mg/g) in a random urine also had increased ACR in a first morning urine. This percentage was higher among individuals ≥50 years old (48.9%), males (53.3%), participants with diagnosed diabetes (56.3%) and hypertension (51.5%), and eGFR <60 mL/min/1.72m(2) (56.9%). The use of confirmed increased ACR (defined as the presence of ACR ≥30 mg/g in both samples taken within 10 days) to define CKD resulted in a lower overall prevalence (11.6%) than first morning urine (12.7%) or random spot urine only (15.2%). CONCLUSIONS: ACR measured on random urine samples appears to overestimate the prevalence of albuminuria compared to first morning urine collections.