Is urinary density an adequate predictor of urinary osmolality?

Autor: Souza AC; Nephrology Service, University of Sao Paulo School of Medicine, São Paulo, SP, Brazil. anacarolinapessoa@gmail.com., Zatz R; Nephrology Service, University of Sao Paulo School of Medicine, São Paulo, SP, Brazil. rzatz@usp.br., de Oliveira RB; Nephrology Service, University of Sao Paulo School of Medicine, São Paulo, SP, Brazil. rodrigobueno.hc@gmail.com.; Nephrology Service, University of Campinas - UNICAMP, Campinas, Brazil. rodrigobueno.hc@gmail.com., Santinho MA; Nephrology Service, University of Sao Paulo School of Medicine, São Paulo, SP, Brazil. mirela.santinho@globo.com., Ribalta M; Nephrology Service, University of Sao Paulo School of Medicine, São Paulo, SP, Brazil. marcia.mribalta@gmail.com., Romão JE Jr; Nephrology Service, University of Sao Paulo School of Medicine, São Paulo, SP, Brazil. joao.egidio@uol.com.br., Elias RM; Nephrology Service, University of Sao Paulo School of Medicine, São Paulo, SP, Brazil. rosilenemotta@hotmail.com.
Jazyk: angličtina
Zdroj: BMC nephrology [BMC Nephrol] 2015 Apr 08; Vol. 16, pp. 46. Date of Electronic Publication: 2015 Apr 08.
DOI: 10.1186/s12882-015-0038-0
Abstrakt: Background: Urinary density (UD) has been routinely used for decades as a surrogate marker for urine osmolality (Uosm). We asked if UD can accurately estimate Uosm both in healthy subjects and in different clinical scenarios of kidney disease.
Methods: UD was assessed by refractometry. Uosm was measured by freezing point depression in spot urines obtained from healthy volunteers (N = 97) and in 319 inpatients with acute kidney injury (N = 95), primary glomerulophaties (N = 118) or chronic kidney disease (N = 106).
Results: UD and Uosm correlated in all groups (p < 0.05). However, a wide range of Uosm values was associated with each UD value. When UD was ≤ 1.010, 28.4% of samples had Uosm above 350 mOsm/kg. Conversely, in 61.6% of samples with UD above 1.020, Uosm was below 600 mOsm/kg. As expected, Uosm exhibited a strong relationship with serum creatinine (Screat), whereas a much weaker correlation was found between UD and Screat.
Conclusion: We found that UD is not a substitute for Uosm. Although UD was significantly correlated with Uosm, the wide dispersion makes it impossible to use UD as a dependable clinical estimate of Uosm. Evaluation of the renal concentrating ability should be based on direct determination of Uosm.
Databáze: MEDLINE
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