These abstracts were presented during the feline stream at College Science Week, the annual congress of the Australian and New Zealand College of Veterinary Scientists, in July.
Biological Variation of Specific Feline Pancreatic Lipase in Clinically Healthy Cats
Margaret Cohn-Urbach1, Craig Ruaux2, Sarah Nemanic2
1Melbourne Veterinary Specialist Centre, Melbourne, Victoria, Australia
2Oregon State University, Corvallis, Oregon, USA
Email: mcohnurbach@melbvet.com.au
Background: Comparison of a specific feline pancreatic lipase (Spec fPL) result against a reference interval is the currently utilised method for determining whether an elevation is likely to be clinically significant. However, to date no biological variation data on Spec fPL in cats have been reported to confirm the appropriateness of this method.
Aim: The objective of this study was to determine biological variation, indices of individuality and reference change values for Spec fPL in order to evaluate the utility of a population-based reference interval for interpretation of Spec fPL.
Methods: Thirteen cats were enrolled in the study. For inclusion, all cats were considered to be healthy based on routine laboratory analysis, Spec fPL and abdominal ultrasonography. Four blood samples were collected at 2 week intervals. At study conclusion, Spec fPL concentrations were measured on all serum samples using commercially available assays.
Results: Intra-individual variation for Spec fPL was calculated at 18.2%; inter-individual variation at 49.3% and analytical variation at 8.7%. Index of individuality for Spec fPL was 2.5, and the two-sided reference change value was 55.8%.
Conclusions: Based on a high index of individuality, use of a population-based reference interval for Spec fPL when screening for pancreatitis will likely underestimate the number of cats with clinically significant elevations. Instead, use of subject-based reference intervals is likely a more sensitive measure for the detection of pancreatitis in cats. A 56% elevation in an individual cat’s Spec fPL result, compared with its baseline value recorded during health, can be regarded as suggestive of a pathological change rather than intra-individual biological variation.
Diagnosis of Feline Leukaemia Virus (FeLV) Infection in Client-Owned Domestic Cats in Australia: Watch Out, False Positives About!
Mark Westman1, Richard Malik2, Evelyn Hall1, Paul Sheehy1, Jacqueline Norris1
1Faculty of Veterinary Science, The University of Sydney, NSW, Australia
2Centre for Continuing Veterinary Education, The University of Sydney, NSW, Australia
Email: mark.westman@sydney.edu.au
Background: Feline leukaemia virus (FeLV) is a complicated infection to diagnose due to the complex feline host–pathogen relationship that underpins its pathogenesis.
Aim: The objective of the study was to compare the precision of three cage-side FeLV antigen kits (SNAP FIV/FeLV Combo, Witness FeLV/FIV and Anigen Rapid FIV/FeLV), using both blood and saliva as diagnostic specimens.
Methods: Blood (n = 563) and saliva (n = 419) were collected from 491 FeLV-uninfected and 72 FeLV-infected cats (45 antigen-positive/PCR-positive ‘progressive infections’, 27 antigen-negative/PCR-positive ‘regressive infections’). Detection of FeLV provirus by quantitative PCR (qPCR) was used as the gold standard.
Results: Sensitivity and specificity using whole blood were 63% and 94% for SNAP FIV/FeLV Combo, 57% and 98% for Witness FeLV/FIV, and 57% and 98% for Anigen Rapid FIV/FeLV, respectively. The SNAP kit had a lower specificity using blood than the other two kits (P = 0.004 cf. Witness; P = 0.007 cf. Anigen). False-positive test results occurred with all three kits using blood. Although using any two kits in parallel increased specificity, no combination of kits completely eliminated false-positive results. FeLV cycle threshold (CT) values for progressively FeLV-infected cats (median 22, range 14–37) were significantly lower (ie, higher proviral load) compared with regressively FeLV-infected cats (median 35, range 29–40) (P <0.001, Mann–Whitney U-test). Progressively FeLV-infected cats were younger (median age 3.4 years) than regressively FeLV-infected cats (median age 7.6 years; P = 0.007). For saliva testing, sensitivity and specificity were 54% and 100%, respectively, for all three test kits.
Conclusions: Confirmatory FeLV provirus PCR testing is required for any cat that has tested positive with a cage-side FeLV antigen kit, as well as for any cat that has been potentially exposed to FeLV but has tested negative with an FeLV antigen kit. In the absence of PCR testing, final assignment of FeLV status cannot be made with confidence. Where PCR testing is unavailable, or rapid confirmation of a positive p27 result is required, repeat p27 testing with a different rapid kit reduces (but does not completely eliminate) the occurrence of false-positive results. The proviral qPCR CT value may be useful to determine whether the infection is progressive (CT <30) or regressive (CT >30). Reduced sensitivity of saliva testing compared with blood testing suggests that saliva is unsuitable for screening large populations of cats.
Assessment of Renal Disease in Cats by Sdma, Creatinine Assessed by Population Reference Interval and Creatinine Assessed by Reference Change Value
Randolph Baral
Paddington Cat Hospital, Sydney, NSW, Australia
Email: rbaral@catvet.com.au
Background: Symmetric dimethylarginine (SDMA) has recently been advocated as a marker to detect renal disease.
Aim: This prospective study evaluated and compared the diagnosis of renal disease using SDMA, creatinine elevated above population-derived reference intervals (RIs) with dilute urine and creatinine in relation to an individual’s prior results (reference change value; RCV).
Methods: Creatinine was assessed on an IDEXX Catalyst Dx analyser. SDMA was assessed on an Olympus AU 400 analyser. A cat was considered to have renal disease if:
Creatinine increased above the provided RI (212 µmol/l) with urine specific gravity (USG) ⩽1.035
Creatinine had an elevated RCV (creatinine had increased by ⩾17% above previously recorded, healthy levels) with USG ⩽1.035
SDMA increased above the provided RI (14 µg/dl) with any (or no) USG.
Results: Over the study period 214 creatinine concentrations (range: 51–1009 μmol/l) were determined from 177 cats. SDMA concentrations (range: 1–115 μg/dl) were available on all occasions; USG was available on 146 occasions (range: 1.008–1.063). RCVs of creatinine (trend) were available on 150 occasions. SDMA, creatinine, creatinine trend and USG were all available on 108 occasions.
Creatinine was within the upper reference limit (<212 µmol/l) on 138 occasions. Of these, SDMA and creatinine by RCV agreed on 106/138 (77%) and 63/84 (76%) occasions, respectively. There were 32 discrepancies with SDMA (23%), of which 23/135 cats (17%) were likely to have renal disease. SDMA had apparent false positives on 9/32 discrepancies (28%). RCV trend/USG detected renal disease on 18/18 occasions (100%) when creatinine by RI (and USG) alone did not. RCV trend/USG missed renal disease detected by SDMA on five occasions (concurrent disease in these cases, mostly gastrointestinal disease). RCV trend was not possible on 54 occasions since no prior results were available. RCV trend/USG and SDMA detected renal disease on 30 occasions when it would not have been detected by increased creatinine by RI (and low USG); ie, creatinine by RI had 30/138 false negatives (22%).
Creatinine was above the upper reference limit (>212 µmol/l) on 76 occasions. SDMA appeared to show at least 15/76 (20%) false negatives. RCV trend was available on 66 of these 76 occasions and was discrepant on 8/66 occasions (12%). No negatives from RCV trend/USG were definitive false negatives. RCV trend/USG and SDMA may detect creatinine by RI false positives.
Conclusions: None of the methods alone were consistently reliable for detection of renal disease. Whether cats with creatinine elevated by RCV (and dilute urine) but without elevated creatinine (by RI) or elevated SDMA represent early detection of renal disease or false positives needs to be investigated further. Cats in this situation warrant further monitoring.
