IDEXX Reference Laboratories Announces Updates to Canine and Feline Creatinine and Total Bilirubin Reference Intervals
As of October, 30th 2017 IDEXX Reference Laboratories will provide updated reference intervals for canine and feline creatinine and total bilirubin results. Comparing an individual patient’s serum creatinine result to a validated reference interval is an important component in determining the health of a patient. Very few laboratories perform their own reference interval studies because of the time commitment and resources required. IDEXX is committed to providing our clients with the most accurate and reliable results possible and have taken the time and committed the resources to generate our own method specific reference intervals based on current scientific recommendations.
How have the creatinine reference intervals changed?
The reference interval for cats is now 80 to 203 µmol/L (previously, 20 to 177 µmol/L).
The reference interval for dogs is now 44 to 133 µmol/L (previously, 20 to 144.5 µmol/L).
How have the total bilirubin reference intervals changed?
The reference interval for cats is now <5.13 µmol/L (previously, 0.1 to 5.1 µmol/L).
The reference interval for dogs is now <5.13 µmol/L (previously, 0.1 to 4.2 µmol/L).
Why were reference intervals changed?
The reference intervals required re-evaluation due to a modification in the method used for measuring creatinine and total bilirubin. For reliable interpretation of results, the patient’s result and the reference interval for creatinine and total bilirubin should be generated using the same method.
How were the new creatinine reference intervals established?
IDEXX followed the Clinical and Laboratory Standards Institute (CLSI) guidelines for determining our new reference intervals.1 Healthy reference populations of dogs and cats were enrolled into the study by participating veterinary hospitals. Reference individuals (>1 year old), characterised as healthy based on history, physical examination, serum biochemistry, haematology and urinalysis results, were used to establish our updated reference intervals. The reference population was not receiving medications except for routine parasite prophylaxis and were of various breeds and sizes.
How will this affect evaluation of trends in canine and feline creatinine results?
Our new reference intervals offer the most appropriate context for interpretation of an individual’s creatinine result. Serial measurement from the same patient to produce a trend in creatinine results can, even when all results are within the reference interval, be of significance. This approach may be particularly helpful in identification and classification of individuals determined by the guidelines of the International Renal Interest Society (IRIS) to be at risk for development of chronic kidney disease or those with IRIS Stage I chronic kidney disease. It is important to note that our new reference intervals will have no effect on IRIS-based classification of patients. This is because the IRIS classification system is primarily based on the absolute creatinine and/or SDMA result (without needing the context of the reference interval).
Will the change to the feline and canine creatinine reference intervals affect interpretation of IDEXX SDMA™ Test results?
The interpretation of IDEXX SDMA results should not change. While creatinine results should be considered when interpreting SDMA, SDMA* will continue to be a more reliable indicator of kidney function. SDMA will increase earlier than creatinine in most cats and dogs with kidney disease and is a more sensitive indicator of kidney function in poorly muscled and older patients. For these reasons, although primarily based on creatinine, current IRIS guidelines have suggested the use of SDMA for the most appropriate treatment recommendations at all stages. When evaluating kidney function, a complete urinalysis should be performed along with the IDEXX SDMA Test and creatinine to determine if inappropriate urine specific gravity, proteinuria, and/or other evidence of kidney disease is present.
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1. CLSI. Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory; Approved Guideline—Third Edition. CLSI document EP28-A3c. Wayne, PA: Clinical and Laboratory Standards Institute; 2008.