Comparison of serum and plasma SDMA measured with point-of-care and reference laboratory analysers: implications for interpretation of SDMA in cats.

OBJECTIVES: Symmetric dimethylarginine (SDMA) reflects the glomerular filtration rate (GFR) in people, dogs and cats. Initial assays used a liquid chromatography-mass spectroscopy (LC-MS) technique. A veterinary immunoassay has been developed for use in commercial laboratories and point-of-care (POC) laboratory equipment. This study sought to: determine POC and commercial laboratory (CL) SDMA assay imprecision; determine any bias of the POC assay compared with the CL assay; calculate observed total error of the POC assay and compare with analytical performance goals; and calculate dispersion and sigma metrics (σ) for POC and CL SDMA methods. METHODS: Two separate studies were performed that assessed: (1) imprecision, determined by evaluation of pooled feline plasma or serum; and (2) bias, assessed by comparing pooled plasma and serum results, as well as paired analyses of clinical samples from a single venepuncture measured using both analysers. Results were assessed in relation to performance goals. Dispersion and σ were calculated for both analysers. RESULTS: Bias between CL and POC analysers was consistent and high numbers of clinical results were outside performance goals across both studies. Imprecision was poor for both analysers for study 1 and improved to within quality goals for the CL analyser for study 2. Dispersion was at least 40%, meaning a measured result of 14 µg/dl represents a range of possible results from 8 µg/dl to 20 µg/dl. CONCLUSIONS AND RELEVANCE: Clinicians should be careful ascribing medical significance to small changes in SDMA concentration, as these may reflect analytical and biological variability. Analyser-specific reference intervals are likely required.

Bias in feline plasma biochemistry results between three in-house analysers and a commercial laboratory analyser: results should not be directly compared.

In-house analysers are commonplace in small animal practices but cannot be calibrated by the operator; therefore, any bias in the generated plasma analyte values cannot be corrected. Guidelines such as grading of renal disease and published reference intervals (RIs) in veterinary textbooks assume plasma biochemistry values generated by different analysers are equivalent. This study evaluated the degree of bias, as well as if bias was constant or proportional, for feline plasma biochemical analytes assessed by three in-house biochemistry analysers compared with a commercial laboratory analyser. Blood samples were collected on 101 occasions from 94 cats and, after centrifugation, plasma was divided into four aliquots. One aliquot was sent to the commercial laboratory and the remaining three were tested using the in-house biochemistry analysers. Results from each analyser were compared with the commercial laboratory results by difference plots and analyses, and by comparing percentages of results within provided RIs. Substantial bias was evident relative to the results of the commercial analyser for at least half of the analytes tested for each machine. In most cases, bias was proportional, meaning that the difference between the methods varied with the concentration of the analyte. The results demonstrate that values obtained from these analysers should not be directly compared and that RIs are not transferable between these analysers. Potential effects of bias on clinical decision-making may be overcome by use of appropriately generated RIs, or reference change values which, for most biochemistry analytes, are more appropriate than subject-based RIs.

Assessments of feline plasma biochemistry reference intervals for three in-house analysers and a commercial laboratory analyser.

For each species, the manufacturers of in-house analysers (and commercial laboratories) provide standard reference intervals (RIs) that do not account for any differences such as geographical population differences and do not overtly state the potential for variation between results obtained from serum or plasma. Additionally, biases have been demonstrated for in-house analysers which result in different RIs for each different type of analyser. The objective of this study was to calculate RIs (with 90% confidence intervals [CIs]) for 13 biochemistry analytes when tested on three commonly used in-house veterinary analysers, as well as a commercial laboratory analyser. The calculated RIs were then compared with those provided by the in-house analyser manufacturers and the commercial laboratory. Plasma samples were collected from 53 clinically normal cats. After centrifugation, plasma was divided into four aliquots; one aliquot was sent to the commercial laboratory and the remaining three were tested using the in-house biochemistry analysers. The distribution of results was used to choose the appropriate statistical technique for each analyte from each analyser to calculate RIs. Provided reference limits were deemed appropriate if they fell within the 90% CIs of the calculated reference limits. Transference validation was performed on provided and calculated RIs. Twenty-nine of a possible 102 provided reference limits (28%) were within the calculated 90% CIs. To ensure proper interpretation of laboratory results, practitioners should determine RIs for their practice populations and/or use reference change values when assessing their patients' clinical chemistry results.

Biological variation and reference change values of feline plasma biochemistry analytes.

This is the first report concerning biological variation and reference change values of feline plasma biochemistry components in the peer-reviewed literature. Biological variation refers to inherent physiological variation of analytes. The ratio of individual biological variation to group biological variation is referred to as an analyte's index of individuality. This index determines the suitability of an analyte to be assessed in relation to population- or subject-based reference intervals. A subject-based reference interval is referred to as a reference change value or critical difference, and is calculated from individual biological variation. Fourteen cats were sampled for plasma biochemistry analysis once weekly for 6 weeks. Samples were stored and then tested at the same time. Results were assessed in duplicate and coefficients of variation for each analyte were isolated to distinguish variation within each subject, between all subjects and by the analyser. From these results, an index of individuality and reference change values were determined for each analyte. Five plasma biochemistry analytes (alkaline phosphatase, alanine aminotransferase, cholesterol, creatinine and globulin) had high individuality and, therefore, subject-based reference intervals are more appropriate; only one analyte (sodium) had low individuality, indicating that population-based reference intervals are appropriate. Most analytes had intermediate individuality so population-based reference intervals should be assessed in relation to subject-based reference intervals. The results of this study demonstrate high individuality for most analytes and, therefore, that population-based reference intervals are of limited utility for most biochemical analytes in cats.

A retrospective analysis of the effects of meloxicam on the longevity of aged cats with and without overt chronic kidney disease.

The study sought to examine the effect of long-term meloxicam treatment on the survival of cats with and without naturally-occurring chronic kidney disease at the initiation of therapy. The databases of two feline-only clinics were searched for cats older than 7 years that had been treated continuously with meloxicam for a period of longer than 6 months. Only cats with complete medical records available for review were recruited into the study.The median longevity in the renal group was 18.6 years [95% confidence interval (CI) 17.5-19.2] and the non-renal group was 22 years [95% CI 18.5-23.8]. The median longevity after diagnosis of CKD was 1608 days [95% confidence interval 1344-1919] which compares favourably to previously published survival times of cats with CKD. In both groups the most common cause of death was neoplasia. Long-term treatment with oral meloxicam did not appear to reduce the lifespan of cats with pre-existent stable CKD, even for cats in IRIS stages II and III. Therefore, to address the need for both quality of life and longevity in cats with chronic painful conditions, meloxicam should be considered as a part of the therapeutic regimen.

Feline low-grade alimentary lymphoma: how common is it?

Low-grade alimentary lymphoma (LGAL) requires histological assessment of biopsies for diagnosis whereas intermediate- (IGAL) and high-grade (HGAL) alimentary lymphoma (AL) can be diagnosed by cytology of intestinal or mesenteric lymph node aspirates. Assessment of the relative frequency of subtypes of AL using histology alone may be skewed towards an increased frequency of LGAL as cases of IGAL or HGAL diagnosed cytologically may not progress to biopsy. We investigated the relative prevalence of AL subtypes diagnosed by both histopathology and cytology among primary accession cases across Australia during a 5-year period. Clinicopathological features of LGAL were compared with those of IGAL/HGAL. Fifty-three cases of AL were identified, including 30 diagnosed by histology (15 LGAL, 13 HGAL, two IGAL) and 23 IGAL/HGAL diagnosed by cytology. LGAL cases comprised 50% of histological diagnoses, but only 28% of all AL. A palpable abdominal mass was more common in IGAL/HGAL (43%) than in LGAL (7%) [odds ratio (OR) 7.6, P = 0.01]. Anaemia was more common in IGAL/HGAL (41%) compared with LGAL (7%) (OR 9.6, P = 0.02). On abdominal ultrasound, a gastrointestinal mural mass was visualised in 41% of IGAL/HGAL and 0% of LGAL (P = 0.01). Where a detailed abdominal ultrasound report was provided, gastric/intestinal wall thickening was the most commonly reported abnormality (82%). In cats with intestinal thickening, a loss of normal layering was more common (P = 0.02) in cats with IGAL/HGAL (71%) compared with those with LGAL (20%). The relative prevalence of LGAL was lower when cases diagnosed by cytology were included in addition to those diagnosed by histology in the study population. The relative frequency with which LGAL is diagnosed has increased since initial reports from this region. A number of significant clinicopathological findings are useful to distinguish LGAL from IGAL/HGAL.

Preliminary post-prandial studies of Burmese cats with elevated triglyceride concentrations and/or presumed lipid aqueous.

A proportion of Burmese cats in Australia have an exaggerated post-prandial triglyceride (TG) response after an oral fat tolerance test (OFTT). The aim of this study was to determine (a) whether Burmese cats with presumed lipid aqueous (PLA) had exaggerated post-prandial triglyceridaemia, (b) if Burmese cats with exaggerated post-prandial triglyceridaemia ('affected' cats) had decreased lipoprotein lipase (LPL) activity and (c) whether affected cats were more insulin resistant than normal Burmese cats. Of cats with a history of PLA, 4/5 were shown to be lipid intolerant (4h TG>4.5mmol/l). Four affected Burmese cats were age, gender and body condition matched to four normal Burmese cats. Serum TG, insulin, non-esterified fatty acids (NEFA), lipoprotein and apolipoprotein concentrations were determined 2 weeks after commencing a standardised high-protein diet, with an OFTT performed 4 weeks later. Affected Burmese cats did not have significantly different fasting insulin, fructosamine, NEFA, apolipoprotein or lipoprotein concentrations compared to control cats. During the OFTT, affected cats had significantly higher 4h and 6h serum TG and NEFA concentrations than normal cats. There was a trend for lower LPL activity, higher insulin concentrations (at 4 and 6h) and higher insulin area under the curve (AUC) during the OFTT in affected Burmese cats compared to controls, although these results failed to reach significance, probably due to the small number of cats studied. Further investigations using larger numbers of cats should focus on reduced LPL activity and insulin resistance as potential causes of delayed TG clearance.

Assessment of the Accutrend GCT and PTS CardioChek meters to measure blood triglyceride concentrations in cats.

Point-of-care (POC) meters that determine whole blood triglyceride (TG) concentrations are used in human medicine to monitor both fasting and post-prandial TG concentrations. The aim of this study was to evaluate their performance for determining feline TG concentrations. A total of 116 venous blood samples were collected from 55 cats. TG concentrations were measured in whole blood using two meters: the Accutrend glucose cholesterol triglyceride (GCT) (GCT: Roche Diagnostics) and PTS CardioChek (PTS - Polymer Technology Systems), and results compared to those determined by a National Association of Testing Authorities (NATA) accredited veterinary laboratory. The GCT was not suitable for use in cats with normal TG concentrations (<0.9 mmol/l), as it overestimated almost 80% of the values; however, this device performed better with TG concentrations between 0.9 and 2.0 mmol/l. The PTS meter performed well in cats with normal TG concentrations, correctly classifying 90% of values as 'normal', and fairly well with TG concentrations <2.0 mmol/l. The PTS meter could be used to determine whether cats have normal fasting TG concentrations or predict mild elevations in serum TG, whereas the GCT meter can only be used to predict cats with elevated TG concentrations. Although both meters have limitations in determining some TG concentrations, the PTS in particular, could be used as a screening tool to distinguish normal cats to those with hypertriglyceridaemia.

Triglyceride response following an oral fat tolerance test in Burmese cats, other pedigree cats and domestic crossbred cats.

Primary lipid disorders causing fasting triglyceridaemia have been documented infrequently in Burmese cats. Due to the known increased risk of diabetes mellitus and sporadic reports of lipid aqueous in this breed, the aim of this study was to determine whether healthy Burmese cats displayed a more pronounced pre- or post-prandial triglyceridaemia compared to other cats. Serum triglyceride (TG) concentrations were determined at baseline and variably at 2, 4 and 6h after ingestion of a high-fat meal (ie, an oral fat tolerance test) in a representative sample of Burmese and non-Burmese cats. The median 4 and 6h serum TG concentrations were significantly higher in Burmese cats (4h - 2.8mmol/l; 6h - 8.2mmol/l) than in other pedigree and domestic crossbred cats (4h - 1.5mmol/l; 6h - 1.0mmol/l). The non-Burmese group had post-prandial TG concentrations ranging from 0.6 to 3.9mmol/l. Seven Burmese cats had post-prandial TG concentrations between 6.6 and 19.0mmol/l, five had concentrations between 4.2 and 4.7mmol/l, while the remaining 15 had post-prandial concentrations between 0.5 and 2.8mmol/l. None of these Burmese cats had fasting triglyceridaemia. Most Burmese cats with a 4 h TG > 6.0 mmol/l had elevated fasting very low density lipoprotein (VLDL) concentrations. This study demonstrates that a proportion of Burmese cats in Australia have delayed TG clearance compared to other cats. The potential repercussions of this observation with reference to lipid aqueous, pancreatitis and diabetes mellitus in Burmese cats are discussed.

Prevalence of feline immunodeficiency virus infection in domesticated and feral cats in eastern Australia.

Serum samples from 340 pet cats presented to three inner city clinics in Sydney Australia, 68 feral cats from two separate colonies in Sydney, and 329 cattery-confined pedigree and domestic cats in eastern Australia, were collected over a 2-year period and tested for antibodies directed against feline immunodeficiency virus (FIV) using immunomigration (Agen FIV Rapid Immunomigration test) and enzyme-linked immunosorbent assay methods (Snap Combo feline leukaemia virus antigen/FIV antibody test kit, IDEXX Laboratories). Western blot analysis was performed on samples in which there was discrepancy between the results. Information regarding breed, age, gender, housing arrangement and health status were recorded for all pet and cattery-confined cats, while the estimated age and current physical condition were recorded for feral cats. The FIV prevalence in the two feral cat populations was 21% and 25%. The majority of FIV-positive cats were male (60-80%). The FIV prevalence in cattery-confined cats was nil. The prevalence of FIV in the pet cat sample population was 8% (27/340) with almost equal prevalence in 'healthy' (13/170) and 'systemically unwell' (14/170) cats. The age of FIV-positive pet cats ranged from 3 to 19 years; all FIV-positive cats were domestic shorthairs with outside access. The median age of FIV-positive pet cats (11 years) was significantly greater than the median age of FIV-negative pet cats (7.5 years: P<0.05). The prevalence of FIV infection in male pet cats (21/172; 12%) was three times that in female pet cats (6/168; 4%; P<0.05). With over 80% of this pet cat population given outside access and continued FIV infection present in the feral population, this study highlights the need to develop rapid, accurate and cost-effective diagnostic methods that are not subject to false positives created by concurrent vaccination against FIV. This is especially important in re-homing stray cats within animal shelters and monitoring the efficacy of the new vaccine, which has not been challenged against Australian strains. The absence of FIV within cattery-confined cats highlights the value in routine screening and indoor lifestyles. This study provides cogent baseline FIV prevalences in three cat subpopulations which can be used for appraising potential disease associations with FIV in Australia.

Successful treatment of a localised CDC Group EF-4a infection in a cat.

Organisms classified within the Center for Disease Control (CDC) Group eugonic fermenter (EF)-4a are facultative anaerobic, Gram-negative coccobacilli, thought to be of the family Neisseriaceae. CDC Group EF-4a is considered a component of normal oral flora in cats and dogs and is most commonly isolated from bite injuries of human patients. Most previously reported cases in cats have involved fatal necrotising pneumonia. We report a localised infection of the retropharyngeal/mandibular tissues in a cat, which responded to surgical drainage and a 5-week course of amoxycillin clavulanate. There are no prior reports of successfully treated EF-4a infections in cats in the literature.

Disseminated Mycobacterium avium infection in young cats: overrepresentation of Abyssinian cats.

Disseminated Mycobacterium avium-intracellulare complex (MAC) infection was diagnosed in 10 young cats (1-5 years of age) from Australia or North America between 1995 and 2004. A further two cats with disseminated mycobacteriosis (precise agent not identified) were recognised during this period. Of the 12, 10 were Abyssinian cats, one was a Somali cat and one was a domestic shorthair cat. None of the cats tested positive for either FeLV antigen or FIV antibody. The clinical course of these infections was indolent, with cats typically presenting for weight loss, initially in the face of polyphagia, with a chronicity of up to several months. Additional clinical features included lower respiratory tract signs and peripheral lymphadenomegaly. A marked diffuse interstitial pattern was evident in thoracic radiographs, even in cats without overt respiratory involvement. Hair clipped to perform diagnostic procedures tended to regrow slowly, if at all. Diagnosis was generally made by obtaining representative tissue specimens from mesenteric lymph nodes, liver or kidney at laparotomy, or from a popliteal lymph node. The primary antecedent event was most likely colonisation of either the alimentary or respiratory tract, followed by local invasion and eventual lymphatic and haematogenous dissemination. Nine cases were treated using combination therapy with agents effective for MAC infection in human patients. Two cats are still undergoing initial therapy and have responded. Of the remaining seven, all responded during long courses (5-14 months) of clarithromycin combined with either clofazimine or rifampicin, and a fluoroquinolone or doxycycline. Of these, three cats remain well (with durations between 2 months and 2 years following therapy); two developed recurrent disease (at 3 months and 2 years, respectively, following therapy) and have restarted therapy. The remaining two cats improved 1 year and 5 months, respectively, after diagnosis but ultimately succumbed. The two cats in which therapy was restarted have improved dramatically. Certain lines of Abyssinian and Somali cats likely suffer from a familial immunodeficiency that predisposes them to infection with slow-growing mycobacteria such as MAC.