Therapeutic Drug Monitoring Service
deltaDOT/RVC Iohexol Assay
Measure of Glomerular Filtration Rate in cats and dogs
We are pleased to announce that the GFR testing service is open and that we are accepting samples again.
The new iohexol assay from deltaDOT/RVC provides a highly accurate measure of glomerular filtration rate. Because GFR is directly correlated with functional renal mass, quantification of GFR is generally accepted as the best measure of renal function.
The test is simple to carry out, safe and provides rapid results.
The quantitative nature of the results also means that repeated assays over an animal’s lifetime enables disease progression to be accurately monitored and the efficacy of treatment established.
Why do the test?
Measurement of GFR can help identify renal dysfunction in a dog or cat that is isosthenuric but not yet azotemic. It may also be useful as a screening tool for older cats or for some dog breeds known to be at risk of nephropathies.
Results may assist in identifying animals that may require more frequent monitoring or are at risk of renal failure. Repeating GFR measurements is advisable as changes of GFR in time are more informative than the absolute GFR value based on a single measurement.
Earlier diagnosis of renal dysfunction may be of benefit to both clients and patients by providing better information on long-term prognosis and enabling protective therapies or diets to be started sooner.
Finally, accurate measurement of GFR could enable the dosage of renally excreted drugs to be adjusted when renal disease is present, or when the drugs being used are potentially nephrotoxic.
Accuracy of test
Serum iohexol concentration is measured using deltaDOT High Performance Capillary Electrophoresis technology. Results are then used to calculate clearance of iohexol. This enables GFR to be accurately determined with only 3 samples after application of a correction formula. In cats, we use the interval reported by Finch et al. in a group of 20 healthy cats (1). For dogs we use the intervals published by Bexfield et al in 2008 (2), which looked at 118 healthy dogs of various breeds, ages, and body weights.
Analyses are carried out to very high laboratory practice standards by highly qualified and experienced staff. All methods used are fully validated with internal and external quality assurance methods in place, so that clients can have full confidence in the results obtained.
How to carry out the test
- Ensure patients are well hydrated and fasted for 12 hours before the study.
- Administer a dose of 300 mg iodine/kg (1 mL/kg Omnipaque 300) intravenously at time 0. Accurately record the initial start time.
- Take serum samples at 2, 3, and 4 hours after administration. A 0 hour sample is not required. 0.5 mL of serum per sample is needed for analysis.
- Send samples and completed submission form (PDF) to the deltaDOT laboratory at the address below. They can be shipped at room temperature but should not be sent on a Friday (ideally early in the week). Please fill in the form as completely as possible (including history and previous laboratory results), as this will help with the clinical interpretation of the results. Turnaround time for analysis is 4-6 working days. Please contact us if you have cases that need processing more rapidly.
London BioScience Innovation Centre
2 Royal College Street
The assay costs £150 + VAT. This includes the analysis of all three samples, as well as the full interpretation provided by specialist vets from The Royal Veterinary College.
Discount price points are available for analysis of 5, 10 and 20 or more samples booked at the same time.
Please contact us for details of this reduced price at the time of booking. Since we anticipate that this test may be performed more than once on the same patient during their lifetime, additional discounts will be added each time the analysis is carried out.
- Is the test safe?
- To date, no adverse drug reaction has been reported with iohexol while carrying out GFR tests in animals.
- Is the test reliable?
- Yes. Several papers have been published on the use of iohexol to accurately measure GFR. A summary of the approaches that have been taken in measuring GFR, including the use of iohexol, can be found in An overview of glomerular filtration rate testing in dogs and cats by Von Hendy-Willson et al. (3)
- Is the test available for animals other than cats and dogs?
- Not at this time.
- Can I order the test if I am not based in the UK?
- Yes, that is not a problem. Iohexol is very stable in serum, but we would recommend that any samples sent from outside the UK are shipped chilled or frozen to allow for the longer delivery time.
References and links
- Finch NC, Syme HM, Elliott J, Peters AM, Gerritsen R, Croubels S, Heiene R. (2011) Glomerular filtration rate estimation by use of a correction formula for slope-intercept plasma iohexol clearance in cats. Am J Vet Res. 72(12):1652-9
- N.H. Bexfield, R. Heiene, R.J. Gerritsen, U. Risoen, K.A. Eliassen, M.E. Herrtage, A.R. Michell (2008) Glomerular filtration rate estimated by 3-sample plasma clearance of iohexol in 118 healthy dogs Journal of Veterinary Internal Medicine 22:66–73
- Von Hendy-Willson VE, Pressler BM, (2011) An overview of glomerular filtration rate testing in dogs and cats The Veterinary Journal 188 (2):156–165
deltaDOT website: www.deltadot.com
If you want any more information on the Iohexol GFR assay, or about our other analytical capabilities, you can contact us at:
- firstname.lastname@example.org (Dr Lesley Caldwell)
- email@example.com (Dr Ludovic Pelligand)