Measurement of urine relative density using refractometer and reagent strips

Performance evaluation of Hipee S2 point-of-care testing urine dipstick analyser: a cross-sectional study

OBJECTIVE

With advances in mobile technology, smartphone-based point-of-care testing (POCT) urinalysis hold great potential for disease screening and health management for clinicians and individual users. The purpose of this study is to evaluate the analytical performance of Hipee S2 POCT urine dipstick analyser.

DESIGN

A multicentre, hospital-based, cross-sectional study.

SETTING

Analytical performance of the POCT analyser was conducted at a clinical laboratory, and method comparison was performed at three clinical laboratories in China.

PARTICIPANTS

Urine samples were collected from 1603 outpatients and inpatients at three hospitals, and 5 health check-up population at one of the hospitals.

OUTCOME MEASURES

All tests were performed by clinical laboratory technicians. Precision, drift, carry-over, interference and method comparison of Hipee S2 were evaluated. Diagnostic accuracy of semiquantitative albumin-to-creatinine ratio (ACR) for albuminuria was carried out using quantitative ACR as the standard.

RESULTS

The precision for each parameter, assessed by control materials, was acceptable. No sample carry-over or drift was observed. Ascorbate solution with 1 g/L had an inhibitory effect for the haemoglobin test. Agreement for specific gravity (SG) varied between moderate to substantial (κ values 0.496-0.687), for pH was moderate (κ values 0.423-0.569) and for other parameters varied between substantial to excellent (κ values 0.669-0.991), on comparing the Hipee S2 with laboratory analysers. The semiquantitative microalbumin and creatinine were highly correlated with the quantitative results. The sensitivity of semiquantitative ACR to detect albuminuria was 87.2%-90.7%, specificity was 70.7%-78.4%, negative predictive value was 85.3%-87.9% and positive predictive value was 73.9%-83%.

CONCLUSIONS

Hipee S2 POCT urine analyser showed acceptable analytical performance as a semiquantitative method. It serves as a convenient alternate device for clinicians and individual users for urinalysis and health management. In addition, the POCT semiquantitative ACR would be useful in screening for albuminuria.

Estimated urinary osmolality based on combined urinalysis parameters: a critical evaluation

Background Urinary conductivity allows a coarse prediction of urinary osmolality in most cases but is insensitive to the osmolal contribution of uncharged particles and the presence of roentgen contrast media. Urinary osmolality can be estimated on the recently introduced Sysmex UF-5000 urine analyzer using conductivity. In this study, we evaluated the analytical performance of this research parameter. Secondly, we aimed to improve the manufacturer's algorithm for estimating urinary osmolality, based on standard urinalysis parameters (creatinine, glucose, relative density). Methods The analytical performance was determined and a prediction model to estimate urinary osmolality based on urinalysis parameters was developed. We further developed and validated a prediction model using another set of routine urine samples. In addition, the influence of roentgen contrast media on urinary osmolality was studied. Results The within-run and between imprecision for osmolality and conductivity measured on the Sysmex UF-5000 ranged from 1.1% to 4.9% and 0.7% to 4.8%, respectively. Multiple regression analysis revealed urinary creatinine, conductivity and relative density to be the strongest predictors to estimate urinary osmolality. A mean difference of 1.3 mOsm/kg between measured and predicted osmolality demonstrated that the predictive performance of our model was favorable. An excellent correlation between the relative density and % contrast media was demonstrated. Conclusions Urinary osmolality is an important parameter for assessing specimen dilution in urinalysis. Urinary conductivity, along with relative density and urinary creatinine allows a coarse prediction of urinary osmolality and is insensitive to the osmolal contribution of uncharged particles and the presence of roentgen contrast media.

Diabetes Insipidus and Syndrome of Inappropriate Antidiuretic Hormone in Critically Ill Patients

Diabetes insipidus and the syndrome of inappropriate antidiuretic hormone secretion lie at opposite ends of the spectrum of disordered renal handling of water. Whereas renal retention of water insidiously causes hypotonic hyponatremia in syndrome of inappropriate antidiuretic hormone secretion, diabetes insipidus may lead to free water loss, hypernatremia, and volume depletion. Hypernatremia and hyponatremia are associated with worse outcomes and longer intensive care stays. Moreover, pathologies causing polyuria and hyponatremia in patients in intensive care may be multiple, making diagnosis challenging. We provide an approach to the diagnosis and management of these conditions in intensive care patients.

Progress in Automated Urinalysis

New technological advances have paved the way for significant progress in automated urinalysis. Quantitative reading of urinary test strips using reflectometry has become possible, while complementary metal oxide semiconductor (CMOS) technology has enhanced analytical sensitivity and shown promise in microalbuminuria testing. Microscopy-based urine particle analysis has greatly progressed over the past decades, enabling high throughput in clinical laboratories. Urinary flow cytometry is an alternative for automated microscopy, and more thorough analysis of flow cytometric data has enabled rapid differentiation of urinary microorganisms. Integration of dilution parameters (e.g., creatinine, specific gravity, and conductivity) in urine test strip readers and urine particle flow cytometers enables correction for urinary dilution, which improves result interpretation. Automated urinalysis can be used for urinary tract screening and for diagnosing and monitoring a broad variety of nephrological and urological conditions; newer applications show promising results for early detection of urothelial cancer. Concomitantly, the introduction of matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) has enabled fast identification of urinary pathogens. Automation and workflow simplification have led to mechanical integration of test strip readers and particle analysis in urinalysis. As the information obtained by urinalysis is complex, the introduction of expert systems may further reduce analytical errors and improve the quality of sediment and test strip analysis. With the introduction of laboratory-on-a-chip approaches and the use of microfluidics, new affordable applications for quantitative urinalysis and readout on cell phones may become available. In this review, we present the main recent developments in automated urinalysis and future perspectives.

Study on a novel core module based on optical fiber bundles for urine dry-chemistry analysis

A core module with a novel optical structure is presented to analyze urine by the dry-chemistry method in this paper. It consists of a 32-bit microprocessor, optical fiber bundles, a high precision color sensor and a temperature sensor. The optical fiber bundles are adopted to control the spread path of light and reduce the influence of ambient light and the distance between the strip and sensor effectively. And the temperature sensor is applied to detect the environmental temperature to calibrate the measurement results. Therefore, all these can bring a lot of benefits to the core module, such as improving its test accuracy, reducing its volume and cost, and simplifying its assembly. Additionally, some parameters, including the calculation coefficient about reflectivity of each item, semi-quantitative intervals, the number of test items, may be modified by corresponding instructions in order to enhance its applicability. Meanwhile, its outputs can be chosen among the original data, normalized color values, reflectivity, and the semi-quantitative level of each test item by available instructions. Our results show that the module has high measurement accuracy of more than 95%, good stability, reliability, and consistency and can be easily used in various types of urine analyzers.

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.

Solution densities and estimated total protein contents associated with inappropriate flotation of separator gel in different blood collection tubes

CONTEXT

Clinical samples that have densities greater than that of separator gel in specimen tubes may exhibit gel flotation to the top of the specimen upon centrifugation. Inappropriate separator gel flotation can occur in specimens with high protein content. In automated analytical systems, gel flotation can lead to mechanical disruption and potential inaccurate result reporting upon aspiration into instrument sampling probes.

OBJECTIVE

To determine the relative specimen densities and estimated total protein contents at which specimen gel flotation would occur upon centrifugation in commonly used commercial specimen tubes, a comparative study of separator gel density was initiated using prepared dextran solutions.

DESIGN

Specific gravity of several dextran solutions was determined by direct hydrometry. The dextran solutions were introduced to serum and plasma lithium heparin BD Vacutainer specimen tubes manufactured by Becton, Dickinson and Company and into Vacuette specimen tubes manufactured by Greiner Bio-One containing separator gel. Following centrifugation the specimen tubes were examined for gel flotation.

RESULTS

Flotation was observed at a lower dextran solution density for Greiner than for BD tubes in both serum and plasma separator gel specimen tubes. Additionally, some differences between specimen tube lots were observed for both BD and Greiner tubes. The total protein content in clinical samples that would result in gel flotation can be estimated for different specimen container types.

CONCLUSIONS

Differences were observed for the gel separator specific gravity in different blood collection containers. Laboratories wishing to avoid problems with inappropriate gel flotation in high protein samples should consider these observations.

Dipstick measurements of urine specific gravity are unreliable

AIM

To evaluate the reliability of dipstick measurements of urine specific gravity (U-SG).

METHODS

Fresh urine specimens were tested for urine pH and osmolality (U-pH, U-Osm) by a pH meter and an osmometer, and for U-SG by three different methods (refractometry, automatic readout of a dipstick (Clinitek-50), and (visual) change of colour of the dipstick).

RESULTS

The correlations between the visual U-SG dipstick measurements and U-SG determined by a refractometer and the comparison of Clinitek((R))-50 dipstick U-SG measurements with U-Osm were less than optimal, showing very wide scatter of values. Only the U-SG refractometer values and U-Osm had a good linear correlation. The tested dipstick was unreliable for the bedside determination of U-SG, even after correction for U-pH, as recommended by the manufacturer.

CONCLUSIONS

Among the bedside determinations, only refractometry gives reliable U-SG results. Dipstick U-SG measurements should be abandoned.