Dipstick measurements of urine specific gravity are unreliable

Simultaneous uroflowmetry and urinalysis with single specimen - A prospective evaluation of automatic urine strip analyzer of ORUBA INALYS: Uroflowmetry-urinalysis combined device

Objective

To evaluate the consistency of the urinalysis results performed with the ORUBA INALYS device, (Oruba, Ankara, Turkey) which can perform urinalysis and uroflowmetry simultaneously, with the analysis results performed with the SYSMEX UC3500 automated urine chemistry analyzer (Sysmex, Kobe, Japan).

Material and methods

In this prospective study, urinalysis of 50 male patients with lower urinary tract symptoms were evaluated. The parameters of glucose, pH, urobilinogen, bilirubin and ketone, leukocyte, protein, and blood were measured with ORUBA INALYS, and the same urine specimens collected from ORUBA INALYS by a special setup were sent to the laboratory for urinalysis with Sysmex UC-3500 to assess the concordance of the results between two devices.

Results

Urinalysis results in ORUBA INALYS device in terms of glucose, pH, urobilinogen, bilirubin, and ketone parameters were shown to achieve 100% agreement within ±1 category with SYSMEX UC3500 whereas these values were slightly decreased to 88%, 96%, and 98% for leukocyte, protein, and blood, respectively. Among the calculable weighted kappa values for the test parameters, the highest value was found for glucose and followed by blood, pH, leukocyte, and specific gravity respectively.

Conclusion

Significant consistency of the urinalysis results obtained from ORUBA INALYS with those obtained from device SYSMEX UC3500 shows the reliability of the urinalysis performed with ORUBA INALYS. ORUBA INALYS could minimize costs and workload, provide time save and reduce plastic waste.

Diarrhoea, malnutrition, and dehydration associated with school water, sanitation, and hygiene in Metro Manila, Philippines: A cross-sectional study

INTRODUCTION

Diarrhoea, malnutrition, and dehydration threaten the lives of millions of children globally due to inadequate water, sanitation, and hygiene (WaSH). Our study aimed to identify environmental and behavioural risk factors of these health outcomes among schoolchildren in Metro Manila, Philippines.

MATERIALS AND METHODS

We analysed data from a multistage cluster sample of schoolchildren in grades 5, 6, 7, 9, and 10 (ages ~10-15 years old) to investigate WaSH facilities and hygiene practices. Outcomes were: self-reported diarrhoea, measured via questionnaire; observed malnutrition (stunting, undernutrition [underweight/thin and wasted/severely thin], over-nutrition [overweight and obese]), measured via anthropometry; dehydration, measured via urine specific gravity/urine test strips. We used multiple logistic regression to explore correlates.

RESULTS

We included 1558 students from 15 schools in three cities. Over 28% (421) of students had diarrhoea and 68% (956) were dehydrated. Over 15% (227) of students were stunted, ~9% (127) were undernourished, and >21% (321) were over-nourished. Diarrhoea was associated with poor handwashing, while dehydration was associated with the lack of water in school restrooms. Stunting was linked with not using the school restroom, the lack of water in school restrooms, and the lack of hygiene lessons in school. Undernutrition was associated with the lack of a school restroom cleaning policy. Risks of diarrhoea, stunting, and undernutrition decreased as the number of school restrooms increased. Risks of stunting and overnutrition decreased as the numbers of school toilets increased. Having more than seven handwashing basins was associated with decreased risk of dehydration.

DISCUSSION

Findings from our cross-sectional study cannot describe causation. We have found associations that suggest that school restroom cleaning policies, adequate water supply, improved handwashing, and hygiene education are needed to prevent disease. School-based WaSH interventions are recommended to provide water in school WaSH facilities, promote handwashing, and improve hygiene-related knowledge.

Automated Urinal-Based Specific Gravity Measurement Device for Real-Time Hydration Monitoring in Male Athletes

Acute and chronic hydration status is important for athlete safety and performance and is frequently measured by sports scientists and performance staff in team environments via urinalysis. However, the time required for urine collection, staff testing, and reporting often delays immediate reporting and personalized nutrition insight in situations of acute hydration management before training or competition. Furthermore, the burdensome urine collection and testing process often renders chronic hydration monitoring sporadic or non-existent in real-world settings. An automated urinalysis device (InFlow) was developed to measure specific gravity, an index of hydration status, in real-time during urination. The device was strongly correlated to optical refractometry with a mean absolute error of 0.0029 (±0.0021). Our results show this device provides a novel and useful approach for real-time hydration status via urinalysis for male athletes in team environments with high testing frequency demands.

Comparison of different methods used in drugs of abuse for sample validity testing including pH methods, specific gravity methods, TECO™ Drug Adulteration Test Strip and oxidant assay

Objectives

In the absence of sample validity testing, a healthcare provider may fail to identify a patient's adulteration of their urine sample. This study compared different methods for specific gravity (SG), pH, TECO™ Drug Adulteration Test Strip (dipstick) and oxidant assay to explain the differences and also make an informative decision on method selection.

Methods

Creatinine, SG and pH measurements are essential in sample validity testing. SG and pH automated chemical methods are compared against pH meter method, SG refractometer and dipstick method. Also, oxidant assay was compared against dipstick method.

Results

SG chemical method agreement with refractometer is 81.9% and with dipstick method is 64.7%. The refractometer method agreement with dipstick method is 66.1%. pH chemical method agreement with pH Meter method is 74.3% and with dipstick method is 81.4%. pH meter method agreement is 85.7% with dipstick method. Results were analysed using Deming regression analysis and F-test. SG chemical method correlated better with refractometer than the dipstick method. Oxidant assay correlated well with dipstick method in detecting adulterants such as pyridinium chlorochromate, nitrite and bleach.

Conclusions

Varying degrees of differences were seen in the SG and pH measurements. These differences were both method and instrument dependent. The automated chemical methods are recommended alongside oxidant assay for consistency, accuracy and faster turn-around time as part of sample validity testing for drugs of abuse.

Estimates of fluid intake, urine output and hydration-levels in women from Somaliland: a cross-sectional study

The study objective was to measure fluid intake and associations with background characteristics and hydration biomarkers in healthy, free-living, non-pregnant women aged 15–69 years from Hargeisa city. We also wanted to estimate the proportion of euhydrated participants and corresponding biomarker cut-off values. Data from 136 women, collected through diaries and questionnaires, 24h urine samples and anthropometric measurements, were obtained with a cross-sectional, purposeful sampling from fifty-two school and health clusters, representing approximately 2250 women. The mean (95 % CI) 24 h total fluid intake (TFI) for all women was 2⋅04 (1⋅88, 2⋅20) litres. In multivariate regression with weight, age, parity and a chronic health problem, only weight remained a predictor (P 0.034, B 0.0156 (l/kg)). Pure water, Somali tea and juice from powder and syrup represented 49⋅3, 24⋅6 and 11⋅7 % of TFI throughout the year, respectively. Mean (95 % CI) 24 h urine volume (Uvol) was 1⋅28 (1⋅17, 1⋅39) litres. TFI correlated strongly with 24 h urine units (r 0.67) and Uvol (r 0.59). Approximately 40 % of the women showed inadequate hydration, using a threshold of urine specific gravity (Usg) of 1⋅013 and urine colour (Ucol) of 4. Five percent had Usg > 1⋅020 and concomitant Ucol > 6, indicating dehydration. TFI lower cut-offs for euhydrated, non-breast-feeding women were 1⋅77 litres and for breast-feeding, 2⋅13 litres. Euhydration cut-off for Uvol was 0⋅95 litre, equalling 9⋅2 urine units. With the knowledge of adverse health effects of habitual hypohydration, Somaliland women should be encouraged to a higher fluid intake.

Impact of rural versus urban setting on kidney markers: a cross-sectional study in South-Kivu, DRCongo

Background

Most studies of chronic kidney disease (CKD) in Sub-Saharan Africa (SSA) have been conducted in urban settings. They relied on GFR estimated from serum creatinine alone and on the inexpensive, convenient urinary dipstick to assess proteinuria. The dipstick for proteinuria has not been directly compared with the gold standard albumin-to-creatinine ratio (ACR) in a large-sized study in SSA. We hereby assessed the influence of rural versus urban location on the level, interpretation, and diagnostic performance of proteinuria dipstick versus ACR.

Methods

In a cross-sectional population-based study of CKD in both urban (n = 587) and rural (n = 730) settings in South-Kivu, Democratic Republic of Congo (DRC), we assessed the prevalence, performance (sensitivity, specificity, positive predictive value and negative predictive value) and determinants of a positive dipstick proteinuria as compared with albuminuria (ACR). Albuminuria was subdivided into: A1 (< 30 mg/g creatinine), A2 (30 to 299 mg/g creatinine) and A3 (≥ 300 mg/g creatinine).

Results

The overall prevalence of positive dipstick proteinuria (≥ 1+) was 9.6 % (95 % CI, 7.9–11.3) and was higher in rural than in urban residents (13.1 % vs. 4.8 %, p < 0.001), whereas the prevalence of albuminuria (A2 or A3) was similar in both sites (6 % rural vs. 7.6 % urban, p = 0.31). In both sites, dipstick proteinuria ≥ 1 + had a poor sensitivity (< 50 %) and positive predictive value (< 11 %) for the detection of A2 or A3. The negative predictive value was 95 %. Diabetes [aOR 6.12 (1.52–24.53)] was a significant predictor of A3 whereas alkaline [aOR 7.45 (3.28–16.93)] and diluted urine [aOR 2.19 (1.35–3.57)] were the main predictors of positive dipstick proteinuria.

Conclusions

ACR and dipstick proteinuria have similar positivity rates in the urban site whereas, in the rural site, dipstick was 2-fold more often positive than ACR. The poor sensitivity and positive predictive value of the dipstick as compared with ACR makes it unattractive as a screening tool in community studies of CKD in SSA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-021-02431-w.

Detection of voluntary dehydration in paediatric populations using non-invasive point-of-care saliva and urine testing

AIM

Voluntary dehydration, or lack of fluid intake despite water availability, is common in otherwise healthy children, and can lead to adverse effects. Most dehydration biomarkers are impractical for routine assessment in paediatric populations. This study aimed to assess two non-invasive hydration assessment tools, urine specific gravity (U_SG ) and a novel point-of-care (POC) salivary osmolarity (SOSM) sensor, in healthy children.

METHODS

Volunteers were tested by colorimetric U_SG and a handheld SOSM system. Observed values were compared against previous studies to determine hydration status, as was the concordance between parameters.

RESULTS

At the common U_SG threshold of 1.020, 42.4% of the 139 healthy children were dehydrated. The same prevalence was found using the 70-mOSM cut-off value. Comparative analysis of SOSM at varying U_SG thresholds demonstrated significantly higher SOSM in dehydrated children with a U_SG  ≥ 1.030 (P = 0.002).

CONCLUSION

At the U_SG threshold of 1.020 and SOSM threshold of 70 mOSM, 42.4% of healthy children were found to be voluntarily dehydrated. Significantly higher SOSM was observed in dehydrated children (U_SG  ≥ 1.030). As the first study on the utility of POC SOSM measurements for detecting dehydration, these results provide a foundation for future POC characterisation of SOSM in other populations and clinical contexts.

Chemotherapy readiness in pediatric oncology: Assessing an automated method to measure urine specific gravity

As part of the evaluation for chemotherapy readiness, urine specific gravity is measured to assess the patient's overall hydration status. Depending on the accuracy of the methods used, patients may be adversely affected by having their chemotherapy delayed or prematurely started. To evaluate the diagnostic accuracy of a new automated urine dipstick readout device (Clinitek), we tested 196 consecutive urine samples for urine specific gravity and compared them with the practical gold standard, a urine refractometer. We found a high correlation between both tools among clean urine samples, but a poor correlation among the pathological urine samples.

The diagnostic performance of human urinary dipsticks to estimate urine pH, specific gravity (SpG), and protein in horses: are they reliable?

Background

Urinalysis is a critical diagnostic test which is performed in routine veterinary medicine practice. In this diagnostic test, semiquantitative measurement of urine biochemical substances is carried out using urinary dipstick. In the current study, we evaluated the diagnostic performance of human urinary dipsticks to estimate pH, specific gravity (SpG), and protein in 80 urine specimens collected from horses. These parameters were measured using two commercial human dipsticks (KP and MN in abbreviation) and quantitative reference methods. The reference methods for pH, SpG, and protein were pH meter, handheld refractometer, and pyrogallol red method, respectively. The correlation between the semiquantitative dipstick analysis and quantitative reference methods was determined using Spearman’s rank correlation coefficient.

Results

In general, our results revealed that the both human urinary dipsticks are unreliable tests for urinary pH, SpG, and protein content in horses. The analysis indicated that there was a poor correlation between the urine dipsticks and reference method (KP: r_S = 0.534 and MN: r_s = 0.485, Ps < 0.001) for protein. Additionally, there was a weak correlation between the results of pH measured using the urine dipsticks and reference method (KP: r_S = 0.445 and MN: r_s = 0.370, Ps < 0.001). Similar findings were obtained for SpG (KP: r_S = 0.285, MN: r_s = 0.338, Ps < 0.001). The estimation of proteinuria using the human dipsticks in horses lacked specificity, as many false positive protein results were obtained.

Conclusion

We observed that the human commercial urinary dipsticks used in this study were not reliable to correctly estimate urine protein, SpG, and pH in horses.

Clinical utility of urine specific gravity, electrical conductivity, and color as on-farm methods for evaluating urine concentration in dairy cattle

Background

Urine concentration (UC) provides clinically useful information concerning hydration status and renal function of animals.

Objectives

To characterize the clinical performance of urine specific gravity measured by optical refractometry (U_SG‐R) or Multistix‐SG urine reagent dipstick (U_SG‐D), urine electrical conductivity using an OAKTON Con 6 conductivity handheld meter (U_EC), urine color (U_Color) using a custom‐designed 8‐point color chart, and urine creatinine concentration (U_Creat) for assessing UC in dairy cattle.

Animals

20 periparturient Holstein‐Friesian cows.

Methods

Urine was obtained by perineal stimulation or urethral catheterization and urine osmolality (U_Osm, reference method), U_SG‐R, U_SG‐D, U_EC, U_Color, and U_Creat determined. Diagnostic test performance was evaluated using Spearman's rho and logistic regression to determine the area under the receiver operating curve (AUC) and optimal cut point for diagnosing hypohydration (U_Osm ≥800 mOsm/kg). P < .05 was considered significant.

Results

The best performing test for diagnosing hypohydration was U_SG‐R (AUC = 0.90) at an optimal cut point ≥1.030. The second‐best performing test was U_EC (AUC = 0.82) at a cut point of ≥23.7 mS/cm, followed by U_Creat (AUC = 0.76) at a cut point of ≥95.3 mg/dL, and U_Color (AUC = 0.74) at a cut point of ≥4 on an 8‐point scale. Urine specific gravity measured by dipstick performed poorly (AUC = 0.63).

Conclusions and Clinical Importance

U_SG‐R and U_EC provide practical and sufficiently accurate methods for measuring UC in dairy cattle. Urine color had moderate clinical utility as a no‐cost cow‐side method for assessing UC, whereas dipstick refractometry is not recommended for assessing UC.

Mobile Technology Application for Improved Urine Concentration Measurement Pilot Study

Objectives: Low hydration has a deleterious effect on many conditions. In the absence of a urine concentrating defect, urine concentration is a marker of hydration status. However, markers to evaluate hydration status have not been well studied in children. The objectives of this paper are to compare measures of thirst and urine concentration in children and to develop a novel mobile technology application to measure urine concentration. Study Design: Children age 12-17 years were selected (n = 21) for this pilot study. Thirst perception, specific gravity (automated dipstick analysis and refractometer), and urine color scale results were correlated to urine osmolality. The technology department developed a mobile technology camera application to measure light penetrance into urine which was tested on 25 random anonymized urine samples. Results: The patients' thirst perception and color scale as well as two researchers color scale did not significantly correlate with osmolality. Correlation between osmolality and hydration markers resulted in the following Pearson coefficients: SG automated dipstick, 0.61 (P 0.003); SG refractometer, 0.98 (P < 0.0001); urine color scale (patient), 0.37 (P 0.10), and light penetrance, -0.77 (P < 0.0001). The correlation of light penetrance with osmolality was stronger than all measures except SG by refractometer and osmolality. Conclusion: The mobile technology application may be a more accurate tool for urine concentration measurement than specific gravity by automated dipstick, subjective thirst, and urine color scale, but lags behind specific gravity measured by refractometer. The mobile technology application is a step toward patient oriented hydration strategies.

Evaluation and analytical validation of a handheld digital refractometer for urine specific gravity measurement

Objectives

Refractometers are commonly used to determine urine specific gravity (SG) in the assessment of hydration status and urine specimen validity testing. Few comprehensive performance evaluations are available demonstrating refractometer capability from a clinical laboratory perspective. The objective of this study was therefore to conduct an analytical validation of a handheld digital refractometer used for human urine SG testing.

Design and methods

A MISCO Palm Abbe™ refractometer was used for all experiments, including device familiarization, carryover, precision, accuracy, linearity, analytical sensitivity, evaluation of potential substances which contribute to SG (i.e. “interference”), and reference interval evaluation. A manual refractometer, urine osmometer, and a solute score (sum of urine chloride, creatinine, glucose, potassium, sodium, total protein, and urea nitrogen; all in mg/dL) were used as comparative methods for accuracy assessment.

Results

Significant carryover was not observed. A wash step was still included as good laboratory practice. Low imprecision (%CV, <0.01) was demonstrated using low and high QC material. Accuracy studies showed strong correlation to manual refractometry. Linear correlation was also demonstrated between SG, osmolality, and solute score. Linearity of Palm Abbe performance was verified with observed error of ≤0.1%. Increases in SG were observed with increasing concentrations of albumin, creatinine, glucose, hemoglobin, sodium chloride, and urea. Transference of a previously published urine SG reference interval of 1.0020–1.0300 was validated.

Conclusions

The Palm Abbe digital refractometer was a fast, simple, and accurate way to measure urine SG. Analytical validity was confirmed by the present experiments.

Validity of HydraTrend reagent strips for the assessment of hydration status

Hydration is used by athletic governing organizations for weight class eligibility. The measurement of urine specific gravity (USG) as a measure of hydration by reagent strips is a controversial issue. The purpose of this study was to determine the validity of HydraTrend reagent strips that facilitate the correction of USG for alkaline urine samples against refractometry for the assessment of USG. Fifty-one participants (33 males, age = 22.3 ± 1.3 years; 18 females, age = 22.4 ± 1.2 years) provided 84 urine samples. The samples were tested for USG using refractometry and reagent strips and for pH using reagent strips and a digital pH meter. Strong correlation coefficients were found between refractometry and reagent strips for USG (rs(82) = 0.812, p < 0.01) and between reagent strips and pH meter for pH (rs(82) = 0.939, p < 0.01). It was observed that false negative results for National Collegiate Athletic Association (NCAA) requirements (fail refractometry with USG >1.020, pass reagent strips with USG ≤1.020) occurred 39% (33/84) of the time and false negative results for National Federation of State High School Association (NFHS) requirements (fail refractometry with USG >1.025, pass reagent strips with USG ≤1.025) occurred 14% (12/84) of the time. There were no false positives (pass refractometry and fail reagent strips) for NCAA or NFHS requirements. These data show that refractometry and reagent strips have strong positive correlations. However, the risk of a false negative result leading to incorrect certification of euhydration status outweighs the benefits of the HydraTrend reagent strips for the measurement of USG.

Performance Evaluation of Three URiSCAN Devices for Routine Urinalysis

BACKGROUND

This study compares the diagnostic performance (in routine urinalysis) of three URiSCAN devices and three Roche analyzers to manual microscopy and quantitative assays.

METHODS

We analyzed eight dipstick tests using three URiSCAN devices. The results were compared to those of the tests performed using three Roche analyzers. The results of leukocyte and erythrocyte screens were compared to those obtained using manual microscopy. Protein, glucose, pH, and specific gravity (SG) assays performed on the URiSCAN devices were compared with the results of corresponding quantitative assays.

RESULTS

The rates of agreement within one grade difference were found to be more than 94.3%. When compared with manual microscopy, the Optima provided better diagnostic performance for the detection of leukocytes compared with the Urisys 1100. Compared to the Urisys 2400, the Super plus provided better diagnostic performance with regard to both leukocytes and erythrocytes. There was good correlation between the three URiSCAN devices and each quantitative assay, except for SG detection.

CONCLUSION

There were well correlated results between those of the three URiSCAN devices and those obtained using the corresponding Roche analyzers, quantitative assays, and manual microscopy. URiSCAN series devices are therefore suitable for routine urinalysis in clinical laboratories.

Is urinary density an adequate predictor of urinary osmolality?

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.

A novel way to monitor urine concentration: fluorescent concentration matrices

BACKGROUND

The amount of water found in urine is important diagnostic information; nevertheless it is not yet directly determined. Indirectly, the water content in urine is expressed by its density (specific gravity). However, without the diuresis value it is not possible to determine whether the increase in density of urine is due to a decrease in water secretion or an increase in the concentration of secreted substances. This problem can be solved by the use of fluorescent concentration 3D-matrices which characterise urine concentration through the pφ (or -logφ) value of the first fluorescence centre.

MATERIALS AND METHODS

The urine fluorescent concentration 3D-matrix was created by the alignment of the synchronous spectra of the dilution series of urine starting from undiluted (pφ = 0) to 1000-fold diluted urine (pφ = 3).

RESULTS

Using the fluorescence concentration 3D-matrix analysis of the urine samples from healthy individuals, a reference range was established for the value pφ, determining the normal, concentrated or diluted type of urine. The diagnostic potential of this approach was tested on urine samples from two patients with a chronic glomerulonephritis.

CONCLUSION

The pφ value of the urine fluorescence concentration 3D-matrix analysis determines whether the urine sample falls within the normal, concentrated or diluted type of urine. This parameter can be directly utilised in sportsmen's hydration state monitoring, as well as in the diagnosis and treatment of serious diseases. An important advantage of this novel diagnostic approach is that a 12/24 h urine collection is not required, which predetermines it for use especially within paediatrics.

Differential urinary specific gravity as a molecular phenotype of the bladder cancer genetic association in the urea transporter gene, SLC14A1

Genome-wide association studies (GWAS) identified associations between markers within the solute carrier family 14 (urea transporter), member 1 (SLC14A1) gene and risk of bladder cancer. SLC14A1 defines the Kidd blood groups in erythrocytes and is also involved in concentration of the urine in the kidney. We evaluated the association between a representative genetic variant (rs10775480) of SLC14A1 and urine concentration, as measured by urinary specific gravity (USG), in a subset of 275 population-based controls enrolled in the New England Bladder Cancer Study. Overnight urine samples were collected, and USG was measured using refractometry. Analysis of covariance was used to estimate adjusted least square means for USG in relation to rs10775480. We also examined the mRNA expression of both urea transporters, SLC14A1 and SLC14A2, in a panel of human tissues. USG was decreased with each copy of the rs10775480 risk T allele (p-trend = 0.011) with a significant difference observed for CC vs. TT genotypes (p-value(tukey) = 0.024). RNA-sequencing in the bladder tissue showed high expression of SLC14A1 and the absence of SLC14A2, while both transporters were expressed in the kidney. We suggest that the molecular phenotype of this GWAS finding is the genotype-specific biological activity of SLC14A1 in the bladder tissue. Our data suggest that SLC14A1 could be a unique urea transporter in the bladder that has the ability to influence urine concentration and that this mechanism might explain the increased bladder cancer susceptibility associated with rs10775480.

Unexpected random urinary protein:creatinine ratio results-limitations of the pyrocatechol violet-dye method

Background

For clinicians, it is important to rely on accurate laboratory results for patient care and optimal use of health care resources. We sought to explore our observations that urine protein:creatinine ratios (PrCr) ≥30 mg/mmol are seen not infrequently associated with normal pregnancy outcome.

Methods

Urine samples were collected prospectively from 160 pregnant women attending high-risk maternity clinics at a tertiary care facility. Urinary protein was measured using a pyrocatechol violet assay and urinary creatinine by an enzymatic method on Vitros analysers. Maternal/perinatal outcomes were abstracted from hospital records.

Results

91/233 (39.1%) samples had a PrCr ≥30 mg/mmol, especially when urinary creatinine concentration was <3 mM (94.1%) vs. ≥3 mM (16.4%) (p < 0.001). When using the last sample before delivery, 47/160 (29.4%) had a PrCr ≥30 mg/mmol in diluted urine vs. only 17/160 (15.4%) in more concentrated urine (p < 0.001); PrCr positive results were also more frequent among the 32 (20.0%) women with known normal pregnancy outcome (90.9% vs. 0) (p < 0.001). Using the same analyser, 0.12 g/L urinary protein was ‘detected’ in deionised water. Re-analysis of data from two cohorts revealed substantially less inflation of PrCr in dilute urine using a pyrogallol red assay.

Conclusions

Random urinary PrCr was overestimated in dilute urine when tested using a common pyrocatechol violet dye-based method. This effect was reduced in cohorts when pyrogallol red assays were used. False positive results can impact on diagnosis and patient care. This highlights the need for both clinical and laboratory quality improvement projects and standardization of laboratory protein measurement.

Association of urinary sodium/creatinine ratio and urinary sodium/specific gravity unit ratio with blood pressure and hypertension: KNHANES 2009-2010

BACKGROUND

We investigated the association between urinary sodium/creatinine ratio (U[Na(+)]/Cr) or urinary sodium/specific gravity unit ratio (U[Na(+)]/SGU), estimated from spot urine, and blood pressure (BP) and hypertension.

METHODS

The study population consisted of a total of 9674 adults (4478 men, 5196 women) who participated in the Korea National Health and Nutrition Examination Surveys conducted in 2009 and 2010. Urine levels of sodium and creatinine, urine specific gravity (SG), and BP were measured along with other risk factors of hypertension. SGU is the calculated parameter of (SG-1)×100.

RESULTS

There were significant trends of increasing mean systolic and diastolic BPs and prevalence of hypertension with increasing quartile of U[Na(+)]/Cr and U[Na(+)]/SGU. After adjusting for age, total cholesterol, alcohol drinking, obesity, current smoking, mild renal dysfunction, and diabetes mellitus, the odds ratios (ORs) for hypertension in the top quartile of U[Na(+)]/Cr compared with the bottom quartile were 1.40 in men and 2.68 in women. Similarly, the ORs for hypertension in the top quartile of U[Na(+)]/SGU were 1.29 in men and 3.02 in women after adjustment.

CONCLUSIONS

U[Na(+)]/Cr and U[Na(+)]/SGU are associated with BP and hypertension, supporting the possible clinical value of U[Na(+)]/Cr and U[Na(+)]/SGU in general medical facilities.

The impact of temperature and urinary constituents on urine viscosity and its relevance to bladder hyperthermia treatment

PURPOSE

The aim of this study was to determine the kinematic viscosity of human urine and factors associated with its variability. This value is necessary for accurate modelling of fluid mechanics and heat transfer during hyperthermia treatments of bladder cancer.

MATERIALS AND METHODS

Urine samples from 64 patients undergoing routine clinical testing were subject to dipstick urinalysis and measurement of viscosity with a Cannon-Fenske viscometer. Viscosity measurements were taken at relevant temperatures for hyperthermia studies: 20 °C (room temperature), 37 °C (body temperature), and 42 °C (clinical hyperthermia temperature). Factors that might affect viscosity were assessed, including glucosuria, haematuria, urinary tract infection status, ketonuria and proteinuria status. The correlation of urine specific gravity and viscosity was measured with Spearman's rho.

RESULTS

Urine kinematic viscosity at 20 °C was 1.0700 cSt (standard deviation (SD) = 0.1076), at 37 °C 0.8293 cSt (SD = 0.0851), and at 42 °C 0.6928 cSt (SD = 0.0247). Proteinuria appeared to increase urine viscosity, whereas age, gender, urinary tract infection, glucosuria, ketonuria, and haematuria did not affect it. Urine specific gravity was only modestly correlated with urine viscosity at 20 °C (rho = 0.259), 37 °C (rho = 0.266), and 42 °C (rho = 0.255).

CONCLUSIONS

The kinematic viscosity of human urine is temperature dependent and higher than water. Urine specific gravity was not a good predictor of viscosity. Of factors that might affect urine viscosity, only proteinuria appeared to be clinically relevant. Estimates of urine viscosity provided in this manuscript may be useful for temperature modelling of bladder hyperthermia treatments with regard to correct prediction of the thermal conduction effects.

Development of hydration strategies to optimize performance for athletes in high-intensity sports and in sports with repeated intense efforts

Hypohydration - if sufficiently severe - adversely affects athletic performance and poses a risk to health. Strength and power events are generally less affected than endurance events, but performance in team sports that involve repeated intense efforts will be impaired. Mild hypohydration is not harmful, but many athletes begin exercise already hypohydrated. Athletes are encouraged to begin exercise well hydrated and - where opportunities exist - to consume fluid during exercise to limit water and salt deficits. In high-intensity efforts, there is no need, and may be no opportunity, to drink during competition. Most team sports players do not drink enough to match sweat losses, but some drink too much and a few may develop hyponatremia because of excessive fluid intake. Athletes should assess their hydration status and develop a personalized hydration strategy that takes account of exercise, environment and individual needs. Pre-exercise hydration status can be assessed from urine markers. Short-term changes in hydration can be estimated from the change in body mass. Sweat salt losses can be determined by collection and analysis of sweat samples. An appropriate drinking strategy will take account of pre-exercise hydration status and of fluid, electrolyte and substrate needs before, during and after exercise.

Is specific gravity a good estimate of urine osmolality?

CONTEXT

Urine specific gravity (USG) is often used by clinicians to estimate urine osmolality. USG is measured either by refractometry or by reagent strip.

OBJECTIVE

We studied the correlation of USG obtained by either method with a concurrently obtained osmolality.

DESIGN

Using our laboratory's records, we retrospectively gathered data on 504 urine specimens on patients on whom a simultaneously drawn USG and an osmolality were available. Out of these, 253 USG's were measured by automated refractometry and 251 USG's were measured by reagent strip. Urinalysis data on these subjects were used to determine the correlation between USG and osmolality, adjusting for other variables that may impact the relationship. The other variables considered were pH, protein, glucose, ketones, nitrates, bilirubin, urobilinogen, hemoglobin, and leukocyte esterase. The relationships were analyzed by linear regression.

RESULTS

This study demonstrated that USG obtained by both reagent strip and refractometry had a correlation of approximately 0.75 with urine osmolality. The variables affecting the correlation included pH, ketones, bilirubin, urobilinogen, glucose, and protein for the reagent strip and ketones, bilirubin, and hemoglobin for the refractometry method. At a pH of 7 and with an USG of 1.010 predicted osmolality is approximately 300  mosm/kg/H(2)O for either method. For an increase in SG of 0.010, predicted osmolality increases by 182  mosm/kg/H(2) O for the reagent strip and 203  mosm/kg/H(2)O for refractometry. Pathological urines had significantly poorer correlation between USG and osmolality than "clean" urines.

CONCLUSION

In pathological urines, direct measurement of urine osmolality should be used.

Body fluids and salt metabolism - Part I

There is a high frequency of diarrhea and vomiting in childhood. As a consequence the focus of the present review is to recognize the different body fluid compartments, to clinically assess the degree of dehydration, to know how the equilibrium between extracellular fluid and intracellular fluid is maintained, to calculate the effective blood osmolality and discuss both parenteral fluid requirments and repair.

Urine pH is an indicator of dietary acid–base load, fruit and vegetables and meat intakes: results from the European Prospective Investigation into Cancer and Nutrition (EPIC)-Norfolk population study

Evidence exists that a more acidic diet is detrimental to bone health. Although more precise methods exist for measurement of acid–base balance, urine pH reflects acid–base balance and is readily measurable but has not been related to habitual dietary intake in general populations. The present study investigated the relationship between urine pH and dietary acid–base load (potential renal acid load; PRAL) and its contributory food groups (fruit and vegetables, meats, cereal and dairy foods). There were 22 034 men and women aged 39–78 years living in Norfolk (UK) with casual urine samples and dietary intakes from the European Prospective Investigation into Cancer and Nutrition (EPIC)-Norfolk FFQ. A sub-study (n 363) compared pH in casual samples and 24 h urine and intakes from a 7 d diary and the FFQ. A more alkaline diet (low PRAL), high fruit and vegetable intake and lower consumption of meat was significantly associated with a more alkaline urine pH before and after adjustment for age, BMI, physical activity and smoking habit and also after excluding for urinary protein, glucose, ketones, diagnosed high blood pressure and diuretic medication. In the sub-study the strongest relationship was found between the 24 h urine and the 7 d diary. In conclusion, a more alkaline diet, higher fruit and vegetable and lower meat intake were related to more alkaline urine with a magnitude similar to intervention studies. As urine pH relates to dietary acid–base load its use to monitor change in consumption of fruit and vegetables, in individuals, warrants further investigation.

Urine specific gravity and other urinary indices: inaccurate tests for dehydration

OBJECTIVE

Urine output, specific gravity, and ketones (urinary indices) are commonly used as an objective means to assess for dehydration and gastroenteritis severity; however, their utility has not been established. The study was designed to evaluate the accuracy of urinary indices as diagnostic tests to identify acute dehydration.

METHODS

We completed a prospective cohort study in the Emergency Department of an urban pediatric hospital. Seventy-nine subjects ages 3 months to 36 months with gastroenteritis, clinically suspected moderate dehydration, and the need for intravenous rehydration were enrolled in the trial. Urine specific gravity and urine ketone levels were determined with bedside calorimetric (dipstick) testing, and urine output during rehydration and observation was measured by commonly used techniques. An internally validated, weight-based criterion standard for the percent dehydration on enrollment was used to identify the cohort of dehydrated subjects. Correlation statistics were calculated for urine output, specific gravity, and ketones. In addition, multilevel tables were created to determine the sensitivity, specificity, and likelihood ratio at varying test cutoff values to detect 3% and 5% dehydration.

RESULTS

Urine specific gravity (r = -0.06, P = 0.64), urine ketones (r = 0.08, P = 0.52), and urine output during rehydration (r = 0.01, P = 0.96) did not correlate with the initial degree of dehydration present. Clinically useful cutoff values for urine specific gravity and ketones to increase or decrease the likelihood of dehydration at the time of enrollment could not be identified.

CONCLUSIONS

Urinary indices are not useful diagnostic tests to identify the presence of dehydration during the initial assessment of children with gastroenteritis.

Using urine specific gravity to evaluate the hydration status of workers working in an ultra-low humidity environment

In environments with ultra-low humidity, workers may have excessive body water loss due to evaporation through the skin, which can lead to dehydration. Before the development of clinical symptoms and signs, concentrated urine may be applied as an early indicator of dehydration. We used urine specific gravity (USG) as a biomarker to evaluate the hydration status of workers working in such an environment. We collected the urine samples from workers at a lithium battery plant during their annual health examination, and the relative humidity of some working areas called "dry rooms" in the plant was 1.5 +/- 1%. We recruited workers in those dry rooms as the exposure group (N=50) and defined the remaining workers, including administration office workers, as the comparison group (N=122). The prevalence of abnormally concentrated urine (USG>1.030) and related factors were compared between these two groups. While the exposure group were younger and had shorter employment durations compared to the comparison group (p<0.05), they had a higher prevalence of abnormally concentrated urine (p<0.01). After adjusting for age, gender, employment duration, and body surface area, we found that working in the dry rooms was associated with an odds ratio of 11.9 (95% confidence interval: 2.5 to 56.9) of having abnormally concentrated urine. Therefore, USG is a good biomarker for evaluating the hydration status of workers working in ultra-low humidity environments, who need proper protection and adequate fluid supply to prevent excess water loss and its adverse health effects.