para traducir

Comparison of Home Monitoring Methods
for Feline Urine pH Measurement

Rose E. Raskin, Kelly A. Murray, Julie K. Levy

Background — Monitoring of urine pH, often done in the patient’s home, is essential for proper clinical treatment and management of conditions such as urolithiasis.

Objective — The purpose of this study was to assess the agreement in pH readings between a standard laboratory method and methods readily available for home monitoring. The influence of refrigerated storage on urine pH was also examined.

Methods — Urine samples were obtained by cystocentesis from 40 clinically healthy cats, and pH was measured within 2 hours of collection. Each sample was evaluated using pH paper, urinalysis reagent strip, 2 brands of portable pH meters (Chek-Mite, Corning, Corning, NY, USA; and Checker 1, Hanna Instruments, Woonsocket, RI, USA), and a standard laboratory benchtop pH meter. Urine samples were refrigerated, and a second pH reading was obtained with the laboratory benchtop meter after 24 hours. The degree of agreement was assessed among the different methods, with the laboratory benchtop pH meter as the reference method.

Results — The closest agreement was obtained with the Chek-Mite portable pH meter and least agreement with the Checker 1 portable pH meter, which had a constant negative bias of 0.31 units due to expiration of the electrode. As expected, pH paper and reagent strips had poor and intermediate agreement, respectively. The reagent strip method had a negative bias of 0.12 units when compared with the benchtop pH meter and wide disagreement at the low pH end. The reagent strip did not agree strongly with the reference method; only 50% of values were within 0.25 pH units of each other. The difference in pH between 0 hours (6.57 ± 0.54) and 24 hours of refrigeration (6.61 ± 0.53) was not considered clinically significant.

Conclusion — Portable pH meters are excellent for monitoring urine pH at home as long as attention is given to electrode maintenance. Urine can be collected at home and kept refrigerated, and pH may be measured reliably within 24 hours using the reference method or a portable pH meter.

Key Words: Cat, instrumentation, method comparison, pH, urinalysis, urine

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Monitoring of urine pH is essential for proper clinical treatment and management of urolith formation. Several variables affect urine pH such as food intake, diet, age, and breed. After ingestion of a meal, urine pH may increase because of postprandial alkaline tide, which is related to increased gastric acid secretions needed for digestion. Protein, minerals, and organic ions in the diet also affect urine pH and are manipulated in special diets used to manage certain uroliths. Feline urolithiasis is an important and difficult disease syndrome to manage medically. Dietary management of stone formation has been an important therapeutic option. Careful monitoring of urine pH is use to assess accuracy of treatment but can be problematic with excited cats. In a cat with chronic urolithiasis that was being treated with an acidifying diet, the urine had struvite crystals and alkaline pH readings, as measured by a pH meter. The veterinarian determined that the stress of a clinic visit caused hyperventilation and subsequent acute respiratory alkalosis, resulting in alkaline urine. A cat with such a reaction to clinical examination would be an ideal candidate for home measurement of urine pH with a portable pH meter. There are several methods used to measure ph including urine reagent strips (dipsticks), pH paper, and pH meters. There are 2 types of pH meters: standard benchtop models and more convenient, less expensive portable models. The use of portable pH meters was evaluated recently in food animals, where they were reliable for measuring the pH of rumen fluid and urine. The purpose of this study was to compare various methods for home monitoring of feline urine pH. Because in some cases home monitoring might not be possible and transport of urine to a clinic would be necessary, we also examined whether refrigeration of urine over a 24-hour period had an effect on pH.



Materials and Methods

Five-milliliter urine samples were obtained by cystocentesis from 40 sedated cats involved in the University of Florida College of Veterinary Medicine feral cat spay/castration clinic (Operation Catnip). An equal number of females and males were used, ages 6 months to 2 years. Medical history was not known, but all cats appeared clinically healthy. Urine color was recorded at the time of collection. Urine pH was measured within 2 hours of collection,and the remainder of the urine was stored in capped 15-mL polystyrene tubes (Fisherbrand, Fisher Scientific, Suwanee, Ga, USA) under refrigeration for 24 hours. Each sample of fresh urine was evaluated using pH paper (pHydrion Vivid 1-11, Micro Essential Laboratory, Brooklyn, NY, USA), urine dipstick (Multistix, Bayer Corporation, Elkhart, Ind, USA), 2 different brands of hand-held portable pH meters (Chek-Mite, Model PS-30, Corning, Corning, NY, USA; Checker 1, Hanna Corning). A small amount of urine was placed on pH paper and dipsticks, and the pH was visually estimated to the nearest 1 pH unit (pH paper) or the nearest 0.5 pH unit (dipsticks). The same individual interpreted the color reaction, thereby eliminating interobserver variability.The manufacturers’ instructions indicated an accuracy of ±1.0 pH units in the range of pH 5.0-8.5 for the pH paper and for the dipstick. Two-point calibration was performed initially for the portable and benchtop pH meters using commercial buffers of pH 4.0 and 7.0; the machines were recalibrated after every 10 readings. Normal and abnormal urinalysis controls (KOVA Liqua-Trol, Hycor Biomedical, Garden Grove, Calif, USA) were used to verify the accuracy of the portable and benchtop pH meters for urine samples. The manufacturers’ reported accuracy was ±0.2 pH units for both portable models
and ±0.01 pH units for the reference method. The electrodes of the portable pH meters (referred to hereafter as Chek-Mite and Checker) were placed in each urine sample and a reading was taken following stabilization of the meter. A benchtop pH meter reading immediately followed these measurements. After 24 hours of refrigeration, samples were allowed to reach room temperature before a second calibrated benchtop pH meter reading was taken. Intra-assay precision was evaluated for both portable models and the benchtop pH meter by repeated measurements, each of normal and abnormal urine control samples. The coefficients of variations calculated as the S 100 divided by the mean, were 0.9%, 0.6%, and 0.4% overall for the Chek-Mite, Checker, and benchtop pH meters, respectively. Using a statistical software package (Analyse-it for Microsoft Excel, Analyse-It, Leeds, UK), several evaluations were performed.The Deming method comparison test and the National Committee for Clinical Laboratory Standards (NCCLS) bias plot5 were used to assess agreement between 2 methods using the 0-hour benchtop pH meter reading as the gold standard or reference method. A paired t-test also was used to compare themean 0-hour and 24-hour pH values as measured with the benchtop pH meter.

Results
Urine color appeared normal for all samples, ranging from light yellow to dark yellow or
orange-yellow without evidence of blood discoloration. Descriptive data for each of the 5 methods was tabulated. There was an average bias of –0.12 and wide disagreement at low pH values for the reagent strip method. For example, a pH of 6 on the dipstick was comparable to a true pH of 5.81-7.18 as measured with the benchtop meter. There was close agreement between the Chek-Mite instrument and the reference method. This portable pH meter was very accurate, and no constant bias was detected. There was poor agreement between the Checker portable pH meter and the reference method. Despite high correlation and the least dispersion in values compared with all other tested methods, the Checker instrument showed a constant bias of –0.31. The Pearson’s coefficient of correlation was 0.99 (data not shown) for these 2 methods. Calibration times for the 2 portable instruments differed, with the Chek-Mite requiring longer to stabilize than the Checker instrument. There was a significant difference (P=.0001) between the initial measurement (0 hour) and that recorded 24 hours postcollection; mean ± SD benchtop pH meter values were 6.57±0.54 and
6.61±0.53, respectively. However, the method comparison tests indicated close agreement, with a bias of 0.04 (0.02-0.06, 95% confidence interval).

Discussion
As expected, pH paper was the least accurate method because of the large unit scale for measurement. The reagent strip indicated a pH of 6 when the actual pH ranged from 5.81 to 7.18 with the reference method. Reagent strips could give a false sense of confidence when monitoring feline urine by suggesting that urine is acidic when it is actually neutral or slightly alkaline. Testing by dipstick was more accurate at higher pH levels, although sample numbers were fewer in this range. These findings agree with those of another study, in which urine dipsticks were less accurate than a standard laboratory pH meter.6 This inaccuracy also has been demonstrated in studies of human urine using Multistix reagent strips. In one study, considerable variation could be attributed to the technologist who performed the test. This difference was still present, however, when use of a semiautomated method eliminated the variation among individuals and subjective interpretations. Dipstick readings were falsely low at a true pH of 16.5 and falsely high at a true pH of Portable pH meters are relatively inexpensive and could be used for home monitoring of feline urine. The tight-fitting regression line and the small bias of 0.010 on the NCCLS test of agreement demonstrated that the Chek-Mite portable pH meter produced readings that were closest to those of the gold standard benchtop pH meter for feline urine.The urine pH values of the Chek- Mite instrument were closer to the benchtop meter readings, but the actual readings took 2-3 minutes longer to stabilize compared with the Checker instrument. The long stabilization time was later attributed to electrode failure, which indicates that electrodes should be checked and replaced as necessary, as per the manufacturer’s suggestion. Despite being the most precisely correlated method, however, the Checker instrument had the poorest agreement by the Deming regression test and NCCLS bias plot. This finding indicates that linear regression tests are not the appropriate procedure for method comparison studies because these tests do not detect systematic errors.9 A type of difference plot method (Altman-Bland) has been advocated for veterinary laboratory tests when neither method being evaluated is regarded as the definitive test method; the difference between the 2 test methods is plotted against the average of the 2 methods.10 The NCCLS EP9-A bias plot method is used when one test method is regarded as the definitive test method; the difference between the 2 test methods is plotted against the reference method. The constant bias of –0.31 in the Checker instrument could not be explained as a calibration failure because calibration was performed before use and after every 10 samples. In some cases, systematic error may be caused by interfering substances such as proteins and lipids or to electrostatic discharges. Information provided by the company indicated that the electrodes in these portable
units are not intended for long-term use, and replacement every 6 months is recommended. The Checker instrument had been purchased within 1 year of its use in this study. Subsequent electrode replacement improved the accuracy of the unit to within 0.1 pH unit of the reference benchtop reading, thus explaining the cause of the constant bias. Despite significant variations in pH between 0 and 24 hours of refrigeration, there was no clinical significance attributed to the mean increase of 0.04 pH units. Thus, pet owners may safely refrigerate urine samples before transport to the clinic for measurement by a portable or benchtop pH meter. Because the vast majority of the urine samples were pH 7 or lower in this study, the effects of sample deterioration were minimal, but these effects may not be minimal in all cases. Change in pH is likely to be more notable with active sediment and
infection caused by urease-containing bacteria. Measurement of feline urine pH should be evaluated with a hand-held meter rather than reagent strips, despite the higher expense over a short period of time.
This approach is very important in managing a disease such as feline urolithiasis in which careful monitoring of urine pH is used to assess efficacy of treatment. Regular electrode maintenance and daily calibration of portable pH meters must be performed to ensure test accuracy.
Urine reagent sticks are useful when obtaining approximations of urine pH, such as in a routine urinalysis, but should not be used when careful monitoring of urine
pH is necessary.

Pointer //*

El pointer ha sido definido como el perro de caza por excelencia, en virtud de sus clásicas formas. Velocísimo e incansable cazador, orgullo de los apasionados de las grandes búsquedas por sus grandes cualidades, que sabe poner de manifiesto sobre terrenos llanos y limpios. Dotado de un finísimo olfato, sabe percibir el más leve olor de cualquier animal, incluso en climas cálidos y secos. Galopador incansable. Las características de su modo de trabajar son la muestra muy firme, erguida y muy expresiva y la guía, decidida y vehemente. Los machos miden de 63 a 68 cm. Con un peso de 20 a 30 Kg. Tiene un tórax bastante ancho, muslos y patas bien desarrollados y musculosos. Pies ovalados, con dedos arqueados. Cola de mediana longitud, gruesa en la base, se va afinando gradualmente hacia la punta, llevada a nivel del cuerpo. El pelaje es fino, corto, rígido, perfectamente liso y lustroso. De color limón y blanco, negro y blanco o tricolor.

LABRADOR RETRIEVER

Raza de perro: Labrador Retriever

Descripción: Tamaño medio, fuerte, sólido y robusto-compacto de aspecto. Cráneo ancho. Color blanco canela, negro y marrón. Orejas medianas colgaderas, mandíbula fuerte, cuello poderoso. Cuerpo ancho y profundo con anchos y fuertes lomos. Talla: altura (machos: 56-60 cm; hembras: 54-56 cm). Pelo corto y denso. Cola ancha, estrechándose conforme se acerca a la punta.

Historia:
Es un perro con instinto de cazador. El Labrador Retriever Procede de las tierras del norte (la península de Terranova), frías y duras jornadas de trabajo de caza conforman un carácter disciplinado. Fue llamado Perro menor de Terranova. Por tanto: resistente al frío, buen nadador. Ayudaba a la caza en tierra firme. El conde de Malmsbury lo llevó a Inglaterra en 1825
Habilidades / Actitudes:
El Perro Labrador Retriever es disciplinado, pacífico, manso, amigable, tranquilo, alegre y no agresivo. Es muy adecuado como perro de familia. Pero necesita mucho ejercicio (hasta 10 km. diarios si se quiere que esté en perfectas condiciones). Buen nadador, vive feliz en zonas donde el mar está próximo. Se hace amigo de los niños muy fácilmente. El Labrador Retriver puede ser un buen cazador. Es obediente y dócil, Bien entrenado se convierte en un compañero decisivo. Es seleccionado como perro lazarillo para invidentes y perro-oído para sordos. También es frecuentemente entrenado para la detección de bombas, minas y de incendios; guardian y de búsqueda y rescate; hasta incluso perro terapia en hospitales. El Perro Labrador tiene buen olfato, fácil de educar y buen carácter para el conjunto de una familia.

Cuidados / Salud:

Cariño y mucho ejercicio. El Perro Labrador es un perro que tiende a la obesidad fácilmente. También sufre a menudo displasia de cadera y codo. Hay que tener cuidado con sus problemas oculares o la hipogluecemia. En general es un perro sano y fácil de cuidar. No necesita muchos cuidados, incluso de su pelo, basta con un cepillado diario. Los cachorros del Labrador Retriever son activos y muy curiosos... una delicia para los más pequeños de la familia. Se hace más sosegado y tranquilo la cumplir el año

Quien no puede resistirse a un Labrador con cara de tierno.?

Lejos el mejor perro. Lo siento Diego. Para mi es mejor que el ovejero alemán.