Evaluation of a Test Index Obtained by Coupling Protein with Specific Gravity of Screening Urine Test

Song-Hee Hahn; Ile-Kyu Park

doi:10.3343/lmo.2015.5.4.204

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Hahn and Park: Evaluation of a Test Index Obtained by Coupling Protein with Specific Gravity of Screening Urine Test

Original Article

Clinical Chemistry

Laboratory Medicine Online 2015; 5(4): 204-210.

Published online: 1 October 2015

DOI: https://doi.org/10.3343/lmo.2015.5.4.204

Evaluation of a Test Index Obtained by Coupling Protein with Specific Gravity of Screening Urine Test

Song-Hee Hahn, M.D., Ile-Kyu Park, M.D.

Department of Laboratory Medicine, Hanyang University Medical Center, Seoul, Korea.

Corresponding author: Ile-Kyu Park. Department of Laboratory Medicine, Hanyang University Medical Center, Guri Hospital, 153 Gyeongchun-ro, Guri 11923, Korea. Tel: +82-31-560-2573, Fax: +82-31-560-2585, ikpark@hanyang.ac.kr

Received 29 December 2014 Revised 22 April 2015 Accepted 23 April 2015

(open-access):

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background

The 24-hr urine protein excretion test is regarded as a standard for quantitative urinary protein analysis; however, collection of urine over 24 hr is troublesome and errors may occur during the process. We obtained a test index reflecting diluted or concentrated urine by coupling the results of a simple and rapid routine urine analysis and evaluated its usefulness as a marker that quantitatively reflects the 24-hr urine protein excretion.

Methods

The estimated urine protein-osmolality ratio (Pro/Osm) was obtained by two linear regression equations between urine dipstick protein and natural logarithm of the protein concentration, and between urine specific gravity (SG) and urine osmolality (Osm). Sensitivity and specificity of 'estimated urine Pro/Osm' and the widely used urine protein-creatinine ratio were evaluated for their efficiency in diagnosing pathological proteinuria and nephrotic proteinuria based on 24-hr urine protein excretion.

Results

Moderate correlations were noted between protein concentration determined by the urine dipstick protein assay and natural logarithm of protein concentration (r=0.86) and between urine SG and urine Osm (r=0.74). The receiver operating characteristics analysis showed that an estimated urine Pro/Osm value of 0.045 had a sensitivity of 91.1% and a specificity of 88.6% for diagnosing pathological proteinuria, and a value of 0.204 had a sensitivity of 100% and a specificity of 80.4% for diagnosing nephrotic proteinuria.

Conclusions

Coupling the results of urine dipstick protein and urine SG determined by the routine analysis will provide additional useful information that will make the screening of renal diseases more cost-effective.

Keywords: Proteinuria, Routine urine analysis, Urine protein-osmolality ratio

Figures and Tables

Fig. 1

Correlation between estimated urine Pro/Osm by the new equation and urine Pro/Cre.

Abbreviations: Pro/Osm, protein/osmolality ratio; Pro/Cre, protein/creatinine ratio.

Fig. 2

ROC analysis of estimated urine Pro/Osm ratio by the new equation for diagnosis of pathological proteinuria (A) and nephrotic proteinuria (B). The values for area under the ROC curves for pathological proteinuria and nephrotic proteinuria were 0.954 (95% confidence interval, 0.917-0.991) and 0.912 (95% confidence interval, 0.852-0.971), respectively.

Fig. 3

ROC analysis of the quantitative urine protein/creatinine ratio for diagnosis of pathological proteinuria (A) and nephrotic proteinuria (B). The values for area under the ROC curves for pathological proteinuria and nephrotic proteinuria were 0.976 (95% confidence interval, 0.965-0.988) and 0.979 (95% confidence interval, 0.967-0.991), respectively.

Table 1

Association of estimated urine Pro/Osm by the new equation and urine Pro/Cre with 24 hr urine protein for diagnosing pathological proteinuria and nephrotic proteinuria

Indices		Pathological proteinuria			Nephrotic proteinuria
		24 hr urine protein			24 hr urine protein
		≥200 mg/day	<200 mg/day		≥3,500 mg/day	<3,500 mg/day
Estimated Pro/Osm	≥ 0.045	51 (91.1)	5 (11.4)	≥ 0.204	8 (100)	18 (19.6)
(mg/dL/mOsm/kg)	< 0.045	5 (8.9)	39 (88.6)	< 0.204	0 (0)	74 (80.4)
(n = 100)		56 (100)	44 (100)		8 (100)	92 (100)
Pro/Cre (mg/mg)	≥ 0.207	191 (95.5)	23 (9.9)	≥ 1.763	39 (100)	36 (9.2)
	< 0.207	8 (4.5)	209 (90.1)	< 1.763	0 (0)	357 (90.8)
(n = 432)		200 (100)	232 (100)		39 (100)	393 (100)

Abbreviations: Pro/Osm, protein/osmolality ratio; Pro/Cre, protein/creatinine ratio.

Notes

This article is available from http://www.labmedonline.org

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