The utility of combined urine dipstick analysis and specific gravity measurement to determine feline proteinuria

Evaluation of a urine dipstick protein to urine specific gravity ratio for the detection of proteinuria in dogs and cats

BACKGROUND

The utility of urine dipsticks for the quantification of proteinuria is limited because of the influence of urine specific gravity (USG). To circumvent the need for urine protein creatinine ratios (UPCR) some have proposed a calculated dipstick urine protein to USG ratio (DUR) for the detection of proteinuria. However, the performance of DUR has not been evaluated in veterinary patients.

OBJECTIVES

Evaluate the correlation between DUR and UPCR, while also assessing the effect of urine characteristics on this relationship and evaluating the performance of DUR in detecting proteinuria.

ANIMALS

Urine samples from 308 dogs and 70 cats.

METHODS

Retrospective cohort study of urinalyses and UPCRs from dogs and cats collected between 2016 and 2021.

RESULTS

Both canine and feline urine samples showed a positive moderate correlation between the UPCR and DUR. The correlation was not influenced by the presence of active urine sediment, glucosuria, or urine pH. In detecting canine urine samples with a UPCR >0.5, an optimal DUR of 1.4 had sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of 89%, 83%, 96%, and 63%, respectively. In detecting feline urine samples with a UPCR >0.4, an optimal DUR of 2.1 had sensitivity, specificity, PPV, and NPV of 70%, 100%, 100%, and 75%, respectively.

CONCLUSIONS AND CLINICAL IMPORTANCE

Use of the DUR can be a relatively reliable method for identification of proteinuria. However, given its poor NPV, the DUR cannot be recommended for exclusion of proteinuric patients.

[Urinalysis in dogs and cats, part 1: physical and chemical urinalysis]

The urinalysis of dogs and cats is an important part of the diagnostic evaluation of urinary tract diseases as well as for the identification of systemic diseases. A routine urinalysis consists of a physical and chemical examination of the urine as well as an examination of the urine sediment. Various urine collection methods (free-catch, catheterization, cystocentesis) are available. Each method has multiple advantages and disadvantages. The appropriate method must be chosen individually for each patient depending on the emphasis of the examination. The urine should ideally be examined within 30 minutes of collection as it is prone to change due to time and storage. Physical examination of the urine consists of the determination of urine color, clarity, and specific gravity which provides information regarding the concentration of the urine. The latter is determined by refractometry and needs to be interpreted in the context of the hydration status of the patient. Chemical examination of the urine consists of the determination of the pH value and the presence of blood/hemoglobin/myoglobin, protein, glucose, bilirubin, urobilinogen, nitrite, and ketones. The use of commercially available urine dipsticks is common. These must be stored and used according to the manufacturer's instructions and when interpreting the results, veterinary aspects need to be taken into consideration. The physical and chemical examinations of the urine represent rapid and readily performable methods that provide important information for the diagnosis or the exclusion of numerous diseases.

Evaluation of a smartphone-based colorimetric method for urinalysis dipstick readings in cats

OBJECTIVES

The aim of the study was to compare the diagnostic performances of a smartphone-based colorimetric method (SBCM) for urinalysis with a semi-automated point-of-care (POC) analyser using standardised solutions and cat urine.

METHODS

Artificial solutions (negative and positive quality controls, and purposely designed artificial urine) and natural urine from 216 cats were used. Two urine reagent strips were simultaneously dipped in each sample. One dipstick was read by the SBCM and the other by the POC analyser at the same time. Results for pH, proteins, bilirubin, 'blood', glucose and ketones were considered. Overall agreement and sensitivity, specificity and accuracy of the SBCM were determined based on selected cut-offs.

RESULTS

For the artificial solutions, 80 comparisons were obtained for each analyte and each expected concentration. The overall agreement (exactly the same result) between the two methods was 78.4%. SBCM sensitivity, specificity and accuracy were 99.0%, 100% and 99.3%, respectively. The correlation between the two methods was almost perfect (Cohen's kappa coefficient = 0.9851). For natural urine samples, the overall agreement (including pH) was 68.6%. Using optimal cut-offs for the SBCM determined from the results of analysis of artificial solutions, the sensitivity, specificity and accuracy of the SBCM were 100%, 76.02% and 80.5%, respectively. In this situation, the correlation between the two methods was moderate (Cohen's kappa coefficient = 0.5401). This was mostly due to a high rate of false-positive results for bilirubin (61.1%).

CONCLUSIONS AND RELEVANCE

With proper cut-off use (ie, considering positive or negative results) the SBCM evaluated here has a perfect sensitivity and appropriate diagnostic performances for proteins, 'blood', glucose and ketones. Based on these experimental data, this method appears suitable for dipstick urinalysis but positive results for bilirubin and proteins have to be confirmed.

Urinary Protein/Creatinine Ratio in Feline Medicine: Reasons to Perform It and Its Role in Clinical Practice-A Retrospective Study

This study aimed at understanding the reasons veterinarians conduct a urinary protein/creatinine ratio (UPCR) in cats, correlating it with signalment, dipstick proteinuria tests, and urine specific gravity (USG) and assessing its role in chronic kidney disease (CKD) diagnosis and monitoring. A retrospective study was conducted, including medical data from cats consulted between 2016 and 2018 in a veterinary teaching hospital and submitted to at least one UPCR measurement. A total of 140 cats were included: 35% non-proteinuric (UPCR < 0.2), 25% borderline proteinuric (0.2 < UPCR < 0.4), and 40% overtly proteinuric (UPCR > 0.4). In contrast to other studies, there was no association between UPCR and male reproductive status. UPCR was mainly requested for CKD diagnosis and monitoring. Correlation between UPCR and combined results from dipstick tests and USG was low and inconsistent. Proteinuric CKD cats had a worse outcome at both 6 (odds ratio (OR 4.04) and 12 months (OR 4.36)), and this finding was more pronounced for severely proteinuric cases in which the OR for death was 4.36 and 6.00 at 6 and at 12 months, respectively. In addition to reinforcing the negative prognostic value of proteinuria, this study stresses the low and the inconsistent agreement between UPCR and the combined results of dipstick tests and USG in cats.

Is proteinuria a rare condition in apparently healthy and sick cats? A feline practice experience (2007-2018)

Background:

Proteinuria is assumed to be less frequent in cats than in dogs and is mainly associated with chronic kidney disease (CKD).

Aim:

The current study aimed to evaluate and compare urine protein-to-creatinine (UPC) values retrospectively in cats visited for comprehensive annual health check or for presenting systemic clinical signs related to CKD.

Methods:

UPC ratio was retrospectively evaluated in 112 owned cats, out of which 51 (45.5%) were apparently healthy cats according to their owners who visited for comprehensive annual health checks and 61 (54.5%) sick cats, presenting systemic clinical signs suggesting CKD, such as weight loss or polyuria/polydipsia, among others.

Results:

Based on UPC, the present study found that 54.5% of all cats included were borderline proteinuric or proteinuric, having increased UPC (UPC ≥ 0.2), with 35.7% included in the sick group and 18.7% in the health-check group. Increased UPC was also statistically associated with azotemia and isosthenuria (urinary-specific gravity between 1,008 and 1,035) in both sick and health-check groups of cats.

Conclusion:

Independent of the reason for their medical visit, it could be concluded that borderline proteinuria and proteinuria were statistically mainly related to CKD in cats. Furthermore, the measurement of UPC could be very useful in the detection and management of CKD in apparently healthy cats during a medical visit for annual health check irrespective of the age.