|Year : 2021 | Volume
| Issue : 6 | Page : 1655-1665
|Spot Urine Protein-to-Creatinine Ratio Compared with Dipstick Proteinuria as a Primary Screening Tool for Renal Disease in a Community Setting
Michael Abel Alao1, O. A. Asinobi2, O. R. Ibrahim3, I. A. Lagunju2
1 Department of Pediatrics, Bowen University Teaching Hospital, Ogbomoso; Bowen University College of Medicine, Iwo, Osun State, Nigeria
2 University College Hospital, Ibadan, Oyo State, Nigeria
3 Federal Medical Center Katsina, Katsina State, Nigeria
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|Date of Web Publication||27-Jul-2022|
| Abstract|| |
The Kidney Disease: Improving Global Outcomes (KDIGO) advocates the use of dipstick proteinuria as a primary screening tool. However, the performance of dipstick urinary for proteinuria has been adjudged to be weak, unreliable with poor predictive value. This study aimed to determine and compare significant proteinuria (SP) using spot urinary protein-to-creatinine ratio (UPr/UCr) as a primary screening tools with dipstick proteinuria among the high-risk African children. This study was a cross-sectional study, involving 33 schools in Ogbomoso land, Southwestern Nigeria. A total of 1316 apparently healthy children were recruited through a multistage sampling technique from both rural and urban communities using a semi-structured questionnaire. Dipstick urinalysis was performed on early morning urine samples. Urinary protein was determined using a turbidimetric method, while Jaffe’s reaction was used to measure urinary creatinine concentration. Statistical analysis was performed using IBM SPSS Statistics version 23.0 for Windows. The prevalence of SP using spot UPr/UCr (≥0.2) and dipstick proteinuria (≥1+) was 18.0% and 0.8%, respectively (P <0.001). Of the 224 subjects with SP using UPr/UCr, the females (140; 20.1%) had higher proportion of SP compared to males (84; 15.4% - P = 0.032). Nephrotic range proteinuria was detected in 9/10 (90%) using UPr/UCr, while urinary dipstick method identified only 3/10 (30%). A biserial correlation coefficient (r = 0.092; P =0.001) and inter-rater agreement (Cohen’s Kappa = 0.01) were poor and McNemar’s test was P<0.0001. In the community, UPr/UCr ratio appeared to perform better than dipstick as a primary screening tool for renal disease and may be adopted in the early detection of SP as a marker of kidney disease against the current KDIGO guideline of dipstick proteinuria.
|How to cite this article:|
Alao M, Asinobi OA, Ibrahim OR, Lagunju IA. Spot Urine Protein-to-Creatinine Ratio Compared with Dipstick Proteinuria as a Primary Screening Tool for Renal Disease in a Community Setting. Saudi J Kidney Dis Transpl 2021;32:1655-65
|How to cite this URL:|
Alao M, Asinobi OA, Ibrahim OR, Lagunju IA. Spot Urine Protein-to-Creatinine Ratio Compared with Dipstick Proteinuria as a Primary Screening Tool for Renal Disease in a Community Setting. Saudi J Kidney Dis Transpl [serial online] 2021 [cited 2022 Aug 14];32:1655-65. Available from: https://www.sjkdt.org/text.asp?2021/32/6/1655/352426
| Introduction|| |
Kidney disease is a huge public health problem with a recent report, showing that about 860 million persons in the world have kidney disease. Children of African descent are three times at odd of developing kidney disease than their Caucasian counterpart. In most low middle-income countries, kidney replacement therapy is not publicly funded and the treatment cost of end-stage kidney disease is prohibitively high and unaffordable, hence the need for early diagnosis and prompt intervention to prevent disease progression.
One of the early markers of renal disease is proteinuria. Clinically significant proteinuria is not only a useful early marker of renal disease, but it also serves as an index of disease severity and a determinant of disease progression.,, The amount of protein excreted by children is usually <4 mg/m2/h or 100 mg/m2/day., This value corresponds to a dipstick urinalysis reading of trace or negative proteinuria or a urinary protein-to-creatinine ratio (UPr/UCr) of <0.5 for children between the ages of 6 and 24 months and <0.2 for older children above two years according to the Kidney Disease: Improving Global Outcomes guideline. Values of UPr/UCr above 0.2 in children over two years of age or urinary dipstick proteinuria of ≥1+ define significant proteinuria.,
Previous efforts at determining the prevalence of proteinuria as an indicator of renal disease in Nigeria community largely utilized dipstick urinalyses.,, However, dipstick urinalyses in the detection of proteinuria as a marker of renal disease have been adjudged poor and unreliable,,, The currently reported prevalence of proteinuria in Nigeria using urinalysis dipstick varies widely from 1.0% to 77.4%, as reported from different parts of the country reflecting its poor reliability.,, Hence, a more reliable tool for urinary protein estimation that is accurate, sensitive, reproducible, perhaps automated, that addresses subject’s hydration status and that is simplified for a point-of-care service would be needed in this context.,, Measurement of UPr/UCr as a primary screening tool using an automated biochemical analyzer may meet the above criteria.,, Thus, this study aimed to determine and compare the prevalence of significant proteinuria using dipstick urinalysis and spot UPr/UCr among schoolchildren aged 5–15 years in Southwestern Nigeria.
| Subjects and Methods|| |
This was a cross-sectional study carried out between July and October 2018 which involved public primary and secondary schools in Ogbomoso community, Southwestern Nigeria. Ogbomoso is an inland community, made up of five local government areas (LGAs). The study took place in Ogo-Oluwa (rural) and Ogbomoso South (urban) LGAs.
The minimum sample size was estimated at 95% level of confidence interval (CI), a margin of error set at 1.5%, and at 90% statistical power using the Cochran’s formula for proportion. A 6% prevalence of proteinuria (using UPr/UCr) reported by Esezobor et al among apparently healthy Nigerian children was used in the sample size calculation.
A multistage sampling technique was used to recruit children for the study [Figure 1]. The five LGAs were stratified into urban and rural. A single LGA was selected randomly by simple balloting from each of the urban and rural stratum representing 40% of the LGAs in Ogbomoso community. The list of the public primary and secondary schools (they constitute about 80% of the schools’ population in the selected LGAs) from the selected LGAs obtained from the Ministry of Education formed the sample frame for the study. Subjects were recruited from 30% (33/109) of the total number of schools in the selected LGAs.
|Figure 1. Flow diagram for selection of 1316 study respondents.|
*Stratified random sampling. LGAs: Local government areas, SRS: Simple random sampling, CBR: Computer-based randomization.
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The number of subject recruited from each school equal to:
N = Population of target school × calculated sample size ÷ total population of the 33 schools
A computer-based randomization using Microsoft Excel 2010 version was used to serially pick the schools using the serial number on the register obtained from the Ministry of Education for each stratum. The number of classes in each school was obtained from the Ministry of Education and detailed out. Thirty percent of the total number of classes in each school was picked by a computer-based randomization with Microsoft Excel 2010 version. The arms in a selected class in a school were detailed out. Simple random sampling was used to select an arm from the selected class. Where only one arm existed in the class, this was chosen automatically. Where more than five arms existed per class for equitable representation, two arms were randomly selected from the classes. Therefore, per school, two classes were selected among which one to two arms were chosen depending on the number of arms per class.
The number of children to be selected in each school was proportionate to the school population. Systematic random sampling was used to select subjects from the chosen arm based on the sample interval determined from the list of the children in the arm.
The inclusion criteria included children aged 5–15 years who were apparently well. The following children were excluded: subjects with fever within one week preceding the study; presence of vomiting and diarrhea with dehydration; children on drugs such as sulfonamides, Vitamin C, penicillin, and cephalosporin.
Training sessions and prefield exercises were held with research assistants who demonstrated ≥95% concordance with the researcher on axillary temperature (to exclude fever), weight, and height measurement prior to recruitment. Study pro forma including the consent and assent forms (where applicable) was distributed in the recruited schools to caregivers through their wards before the date of urine collection.
Height was measured with a stadiometer (Seca® Model: 220, USA) with an accuracy of 0.10 cm. Each subject had his/her height measured in the upright position with his/her shoes removed; back, shoulders, and buttocks perpendicular to the central axis, heels against the footboard, knees together, and arms hanging loosely at the sides and the head in the Frankfurt plane. Weight was measured with a digital bathroom weighing scale (Seca® Model: 762, United Kingdom) with an accuracy of 100 g. The subjects were weighed in plain school uniform; extra clothing such as sweaters was removed and the pockets were emptied.
Each of the study subjects was given a labeled universal bottle. Female subjects and their caregivers were informed on how to wash their vulva area with water and wipe with a clean tissue from the front backward before sample collection to minimize contamination of the specimen. Subjects were encouraged to empty their bladder at bedtime the previous night completely and to collect the first morning urine on awakening at hours between 6:00 and 7:00 am. Six milliliters of midstream first morning urine was collected into a universal bottle and the lid was tightly screwed. On arrival in the school, the collected urine was divided into two aliquots by the research assistants; a part was used for dipstick urinalysis on site and recorded, while the second part was kept in plain cryo bottle in an ice park for transportation to the laboratory for subsequent analysis.
Dipstick urinalysis was performed on the uncentrifuged urine specimen using Combi 9 dipstick test strips with Lot number URS6120036 adhering strictly to the manufacturer’s instructions (ACON Laboratories, Inc. 10125 Mesa Rim Road, San Diego, CA 92121, USA). Urine samples kept in the icepack were transported to the laboratory in batches of 5060 for UPr and UCr assay. The samples were analyzed using Roche-Hitachi Cobas c311 Chemistry Autoanalyzer (Roche Diagnostics GmbHD-68298 Mannheim Germany). Urinary creatinine was assayed using the kinetic Jaffe method, while urinary protein was measured using the turbidimetric method. The urine protein measured in g/L was converted to mg/dL by multiplying by 100. The urine creatinine concentration measured in pmol/L was converted to mg/dL by dividing by 88.4., The protein-to-creatinine ratio was obtained by dividing the urinary protein in mg/dL by urinary creatinine also in mg/dL. Significant proteinuria was defined as dipstick proteinuria ≥30 mg/dL and UPr/UCr ratio ≥0.2 mg/mg, respectively, while nephrotic range proteinuria was defined as dipstick proteinuria ≥300 mg/dL and UPr/UCr ratio ≥2.0 mg/mg, respectively.
Ethical approval was obtained from the Oyo State Research Ethical Review Committee, Ministry of Health, Secretariat, Ibadan, with research approval number/Ref.AD13/479/623. Permission with Ref: INS 75T/163 was obtained from the Ministry of Education, Science and Technology Quality Assurance Department, Oyo State Secretariat, Ibadan, Nigeria. Prior to recruitment, consent was obtained from the parents of the study respondents. In addition, assent was obtained from children older than seven years. All information obtained from the participants was kept strictly confidential.
| Data Analysis|| |
Data collected on the study pro forma were entered into a Microsoft access file and analyzed using IBM Corp Statistical Package for the Social Sciences (SPSS)™ for Windows version 23.0 (Armonk, NY, USA: IBM Corp). Frequencies and proportions were computed for categorical variables such as gender. The means and standard deviations of continuous variables of weight, height, and urinary protein-to-creatinine ratio were computed. Results were presented in tables and figures such as line graphs for better visualization of findings. Kappa statistics was used to determine the level of agreement between methods of determining significant proteinuria (dipstick proteinuria and UPr/UCr ratio). The differences in the paired proportion of the respective proteinuria detected were compared using McNemar test. A point biserial correlation coefficient was used to determine the relationship between the log transformed urinary protein-to-creatinine ratio and the dichotomous dipstick urinalysis. The confidence level was set at 95% and P<0.05 level was significant.
| Results|| |
Social demographic characteristics
Out of the 1316 subjects enrolled in the study, 71 were excluded (52 did not produce urine samples and 19 failed to return their questionnaires), giving a response rate of 94.6%. The remaining 1245 subjects were proportionately recruited from 16 primary and four secondary schools in Ogo-Oluwa LGA; while eight primary and five secondary schools were from Ogbomoso South LGA. Six hundred and fifty-five (52.7%) of the 1245 subjects were recruited from the rural settings. The mean age of the study population was 10.6 ±3.0 years. Five hundred and forty-seven (43.9%) were male.
Of the 1245 subjects who had dipstick urinalyses, only 10 had significant proteinuria giving a proportional prevalence of 0.8% (95% CI: 0.4%-1.5%). Age-adjusted prevalence rate was 0.8% (95% CI: 0.4%–1.5%) using the 2006 census population standard. The peak age prevalence of dipstick proteinuria [Figure 2] was at age 12 years 4/160 (2.5%). Fifty-eight subjects (4.7%) had leukocyturia, while 18 (1.4%) tested positive for hematuria. Nitrite was positive in one subject.
|Figure 2. A line graph showing age specific prevalence of significant proteinuria.|
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Age-specific prevalence of proteinuria
Using spot urine protein-to-creatinine, 224 children had a ratio of ≥0.2, placing the crude prevalence of proteinuria at 224/1245 (18.0%; 95% CI: 15.9–20.2%). The age-adjusted prevalence rate was 20.3% (95% CI: 18.122.6%) using 2006 census results as population standard. The prevalence of proteinuria double peaked, first at age group 5 year; 23/80 (28.8%) and thereafter at age 15 year (23/96, 24.0%). The prevalence of significant proteinuria is at its lowest at age nine (8/80, 10%), as shown in [Figure 2].
Gender-specific prevalence of proteinuria
Of the 224 subjects with significant proteinuria by UPr/UCr ratio, 140 out of 698 (20.1%) were female, while 84 out of 547 (15.4%) were male (P = 0.032). Out of the 10 subjects with significant proteinuria by dipstick urinalysis, 2/10 (20.0%) were female, while eight of the 10 (80.0%) were male (P =0.026).
Nephrotic range proteinuria by dipstick and urine protein creatinine ratio
Ten (0.8%) of 1245 had nephrotic range proteinuria giving a crude prevalence of 0.8% (95% CI: 0.4%–1.5%) by the two methods of assessing for proteinuria. Of these methods, spot UPr/UCr ratio identified 9/10 (90%), while 3/10 (30%) were detected by dipstick method.
Agreement between methods of testing proteinuria
The paired analysis (UPr/UCr and Dipstick) with the McNemar test showed a statistically significant difference in the proportion of proteinuria detected by the methods (McNemar; P<0.001), as shown in [Table 1]. The biserial correlation between the proteinuria detected by the methods was also low (r = 0.092; P =0.001). Seven of the 10 subjects with significant dipstick urinalysis proteinuria were negative for a significant UPr/UCr ratio. The odds for spot UPr/UCr ratio to detect proteinuria was two times higher than the dipstick method. Cohen’s kappa coefficient showed very poor agreement (Kappa = 0.01; 95% CI: -0.015-0.036).
|Table 1. Agreement between urinary protein-to-creatinine ratio and dipstick proteinuria.|
Kappa (κ) = 0.010: 95% confidence interval: -0.015-0.036); mc: McNemar.
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| Discussion|| |
A precise and accurate method for the detection and quantification of proteinuria is key in the evaluation and management of African children who are three times at risk of renal disease compared with Caucasian children., Perhaps, this appeared to be the first community-based study that evaluated the UPr/UCr ratio as a primary marker of renal disease among a large number of Nigeria children, as the few available reports that used UPr/UCr ratio recruited few subjects and are hospital based.,
The wide disparity obtained in the present survey between UPr/UCr ratio (18.0%) and dipstick proteinuria (0.8%) supports the previously document superiority of UPr/UCr ratio over dipstick proteinuria when correlated with the gold standard 24 h urinary protein estimation., The findings in the present study are also in tandem with the misclassification of proteinuria of 0.36–3.52 g/d as as 10–100 mg/dL (subnephrotic ranged proteinuria observed by Khan et al on the basis of which it was suggested that dipstick urinalysis for proteinuria should be excluded in assessment for proteinuria. The wide disparity could also be explained by the inability of the dipstick to detect the presence of other forms of protein, which may be present as reported in the AusDiab study. A high-performance liquid chromatography (HPLC) used in the AusDiab study detected a fourfold prevalence of albuminuria compared with using immunonephelometry method. The explanation behind this was the capability of HPLC method to detect various forms of albumin (immunoreactive and nonimmunoreactive albumin). Urine protein-to-creatinine ratio measures total protein which include all forms of albumin and nonalbumin proteins in contrast with the tetrabromophenol blue impregnated in dipstick urinalysis which is insensitive to the varieties of albumin identified by the HPLC and UPr/UCr ratio. Children, in addition, have a higher prevalence of congenital renal tubular disorder compared with adults., Renal tubular disorders or tubulointerstitial diseases result in loss of low molecular weight proteins in the form of α2 microglobulin, β2 microglobulin, retinol-binding protein, light chain, and post-gamma globulin in the urine.,, Assessing this group of children with dipstick urinalysis for proteinuria may underestimate the true prevalence of proteinuria as a marker of kidney disease, as dipstick urinalysis has a high specificity for albuminuria. An evaluation for total protein, perhaps a UPr/UCr ratio, may therefore be more appropriate in children with mixed glomerular and tubular proteinuria.
A biserial correlation coefficient of 0.092 between the two test methods as obtained in this study is far less than the moderate correlation (r = 0.6; P <0.001) observed by Abitbol et al in a hospital-based study that involved 64 Caucasian children with nephrotic syndrome. The present study involved subjects in a community-based survey with broader spectrum of renal diseases besides nephrotic syndrome to which dipstick urinalysis may be less sensitive, as may have been the case in the study by Abitbol et al Previous reports showed that dipstick proteinuria in screening for proteinuria missed 8%–56% of cases in a sample population, further highlighting a possible reason for the observed disparity.,, The McNemar test of significance for the paired proportions shows 70% discordant result between UPr/UCr and dipstick proteinuria reflecting the higher false-positive value for dipstick urinalysis at subnephrotic range proteinuria as previously reported., The performance of dipstick urinalysis for proteinuria is also poor at nephrotic range proteinuria. The reason could the poor sensitivity of dipstick to proteinuria or its inability to detect other forms of non-albumin proteinuria.,
This study found a prevalence rate of 18.0% for significant proteinuria using UPr/Cr ≥0.2. The 18% prevalence is higher than the 6% reported by Esezobor et al among apparently healthy children aged 18 months to 16 years at the Infectious Diseases Clinic of Lagos University Teaching Hospital, Southwest Nigeria. The study by Esezobor et al is an hospital-based study involving a smaller sample size in a comparative cross-sectional study of 50 apparently well children. In addition, the difference in the method used by Esezobor et al (the sulfosalicylic acid test) compared with the turbidimetry method used in the current study for measuring urine protein could also account for the variation in the reported prevalence. The sulfosalicylic acid is known to form an unstable compound with protein capable of causing a falsenegative result and might perhaps be responsible for a lower prevalence among apparently healthy children. Uzomba et al from Calabar Southern Nigeria reported a much lower prevalence of 1.6% for UPr/UCr ≥0.2 in children 5–12 years. The finding by Uzomba et al was expected as UPr/UCr ratio measured was a post hoc confirmatory test among 28 subjects with persistent proteinuria on dipstick urinalysis rather than a screening test.
The prevalence of 18% (using UPr/UCr ratio) from this study was however lower than the 26.4% prevalence obtained from a mass screening from South Korea by Park et al. However, the study by Park et al utilized a UPr/UCr ratio cutoff value of ≥0.15 compared to ≥0.2 in the present study to define significant proteinuria. The increased prevalence in the report by Park et al could also be consequent on the high-risk nature of the sample population as the subjects were suspected cases of kidney disease from a mass urinary screening from a school program.
With respect to dipstick urinalysis proteinuria, the present study’s prevalence of 0.8% is higher than the 0.3% obtained from a school screening program that involved school students in South Korea. Although the reports were obtained using an early morning urine sample, the lower prevalence may be related to differences in environmental exposures and variation in genetic predisposition to renal diseases compared with the present study population. The present prevalence rate of dipstick proteinuria is lower than documented rates in most parts of Africa. In Southwest Nigeria, Oyediran et al recorded a 3.4% prevalence of proteinuria in the early 1970s among teenagers in a rural area in the outskirts of Ibadan; Onifade and Grange in Lagos recorded a comparatively higher prevalence of 7.5% similar to the prevalence of 7.5% reported by Adesola et al in Imesi-Ile in 2007. The higher prevalence of proteinuria in the study by Oyediran et al involved mainly older children and the teenagers compared with children aged 5–15 years sampled in the present research. The prevalence of proteinuria has been reported to rise with age from several reports.,,, The use of midday urine sample which could have included subjects with exercise and postural induced proteinuria in the studies,, from Southwest Nigeria may account for the higher prevalence of proteinuria than what obtained in the current survey.
The strength of this study includes the fairly large, multistage, population-based study that used UPr/UCr ratio in assessing significant proteinuria in children. The use of early morning urine has the potential to have excluded orthostatic proteinuria and other confounders like exercise-induced proteinuria. This study also used automated means to determine urinary protein and creatinine with a potential to obviate inter-observer errors in contrast with other colorimetric and visually assessed turbidometry or precipitates methods. This study could not have excluded subjects with intermittent proteinuria because of the cross-sectional nature of the study design. A longitudinal study with enormous resources would be required to identify subjects with intermittent proteinuria.
In conclusion, asymptomatic proteinuria is quite prevalent among children in South-West Nigeria. This study confirms the previously reported advantages of UPr/UCr ratio over dipstick in the early detection of asymptomatic proteinuria, which may make it a more appropriate screening tool for renal diseases in children.
| Recommendations|| |
1. Health-care service providers, school health workers, and other appropriate individuals and groups should mount up effective health education to increase the awareness of people on renal disease.
2. Broad-based screening for renal diseases using urinary protein-to-creatinine ratio should be undertaken from time to time to identify children with renal disease early.
| Ethical Approval|| |
Ethics approval was obtained from the Oyo State Research Ethical Review Committee, Ministry of Health Secretariat in Ibadan (Ref. AD13/479/623) and permission (Ref: INS 75T/163) from the ministry of education
| Funding|| |
The authors received some financial support from the International Society of Nephrology for the research.
Conflict of interest: None declared.
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Michael Abel Alao
Department of Pediatrics, Bowen University Teaching Hospital, Box 15, Ogbomoso, Oyo State, Nigeria. E-mail: [email protected]
Source of Support: None, Conflict of Interest: None
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