title: Random spot urine protein to creatinine ratio is a reliable measure of proteinuria in lupus nephritis in Koreans.
abstract: OBJECTIVE
  The accurate assessment of proteinuria is critical for the management of lupus nephritis. Measuring the protein to creatinine (P/C) ratio in random spot urine (RSU) samples has been introduced as an alternative to the 24-hour (24h) urine collection method. However, it remains unclear as to whether the RSU P/C ratio is reliable for assessing lupus nephritis (LN) in routine clinical practice.
  
  
  METHODS
  In total, 275 pairs of 24h urine and RSU samples from 102 patients with biopsy-proven LN were analysed. The correlation and concordance between the P/C ratios in the two sample types were assessed by Pearson or Spearman correlation and intra-class correlation coefficient (ICC) using mixed models for repeated measurements, respectively.
  
  
  RESULTS
  The mean 24h urine P/C ratio was 3.2 ± 4.9. Overall, RSU P/C ratio correlated strongly with the 24h urine P/C ratio (r=0.944, p<0.001) with an excellent agreement (ICC=0.949, 95% confidence interval [CI]: 0.69-1.00). Subgroup analyses revealed that the correlation remained high in class II, III, IV, and V LN (rho=0.868, p<0.001; rho=0.649, p=0.007; r=0.945, p<0.001; and rho=0.900, p=0.001, respectively). The correlation between the 24h urine and RSU P/C ratio in the range of 0.5 to 3 was good (r=0.720, p<0.001) with ICC of 0.659 (95%CI 0.554-0.812). RSU P/C ratio ≥0.5 could predict 24h PCR ≥0.5 with 91.7% sensitivity and 70.2% specificity, whereas RSU P/C ratio ≥1.0 increased specificity up to 94.7%.
  
  
  CONCLUSIONS
  The RSU P/C ratio is an excellent alternative to the 24 hour P/C ratio for assessing the presence of clinically significant proteinuria in LN. RSU P/C ratio >1.0 may prompt directly to a renal biopsy, whereas RSU P/C ratio between 0.5-1.0 should be followed by a confirmatory 24h urine collection.
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea. iachoi@outlook.com
authors.forename: In Ah
authors.initials: IA
authors.lastname: Choi
authors.forename: Jin Kyun
authors.initials: JK
authors.lastname: Park
authors.forename: Eun Young
authors.initials: EY
authors.lastname: Lee
authors.forename: Yeong Wook
authors.initials: YW
authors.lastname: Song
authors.forename: Eun Bong
authors.initials: EB
authors.lastname: Lee
mesh_terms: D000328:Adult; D044466:Asian People; D001706:Biopsy; D003404:Creatinine / Q000652:urine*; D005260:Female; D005500:Follow-Up Studies; D005919:Glomerular Filtration Rate; D006801:Humans; D008181:Lupus Nephritis / Q000175:diagnosis / Q000652:urine*; D008297:Male; D008875:Middle Aged; D011507:Proteinuria / Q000175:diagnosis / Q000652:urine*; D012015:Reference Standards; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013048:Specimen Handling / Q000379:methods; D016482:Urinalysis / Q000379:methods* / Q000592:standards*; D055815:Young Adult
chemical_list: D003404:Creatinine