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This IssueThis month we look at some aspects of small animal endocrinology, a rapidly growing areas of investigation in both general practice and the laboratory.This is an area where test recommendations can change rapidly, previously unreported disorders are recognised, approaches to treatment are constantly refined and expanded. Keeping up to date can be a problem. The control of diabetes mellitus in dogs and increasingly cats is an every day problem in moth practices. We look at lab tests which can help with stabalisation and control. Also the diagnosis of some of the underlying causes of instability. example investigating thyroid disorders. In the USA the "Gold Standard" test for the investigation of thyroid disorders is the determination of Free T4 by equilibrium dialysis (FT4D) and has been for a number of years. The test for Free T4 by equilibrium dialysis is now available from North Western Laboratories We highlight the application of this test as an aid to the diagnosis of thyroid disorders in both cats and dogs. Back The Unstable Diabetic Dog - improve controlOccasionally the stabilisation of an apparently uncomplicated case of canine diabetes mellitus will not run smoothly, or a previously apparently stable case ‘wobbles’ badly. Once it has been established that the insulin is OK (within date and correctly stored and treated), that there is no problem with administration (the dog is not suddenly in the care of Auntie Molly whose technique is somewhat wanting) and that nothing else has changed in the daily routine then it is time to consider the patient.Common Problem A common problem is the patient who apparently needs persistently high or increasing amounts of insulin. Another is the case whose requirements fluctuate dramatically. Whatever the problem, creation of a glucose curve can be a very useful step in understanding the situation. The patient is usually admitted for ease of access. Insulin is administered and meals offered at the usual times and samples for blood glucose are taken every two hours for 18-24 hours. The resulting curve, with meals and insulin administration marked can be illuminating. Case History One comparatively common case is that of the middle aged bitch who has recently been in season. Metoestrus can induce insulin resistance. A recent case featured a little collie cross who was not known to have been in season for the last two years. Serum progesterone levels indicated that she was in fact in metoestrus and ovaro-hysterectomy effectively solved the problem. Other concurrent diseases will require appropriate investigation. We will be happy to help sort out problem cases. Back The Unstable Diabetic Cat - improve controlDiabetes mellitus is a more complex disease in cats than in dogs. Cats may have an absolute insulin deficiency due to loss of functional pancreatic beta-islet cells, a relative insulin deficiency similar to type II diabetes in man or secondary diabetes arising from a variety of causes, including pancreatitis, hyperadrenocorticism, drug therapy with glucocorticoids or progestogens.Testing Helps The control of diabetes can be improved initially by checking the Glucose Curve by checking glucose values at 2 hour intervals over a 24 hr period. Once insulin dosage has been established the use of serum fructosamine to assess glycaemic control over the initial stabilisation period should be considered. Fructosamine is less affected by the stress of the clinical environment and repeated venepuncture. During the initial stabilisation period fructoasmine should be measured every 2 weeks. Once stability has been achieved testing intervals can be increased to every 2 months. Concurrent Disease Concurrent disease which may contribute to poor control should be evaluated. Chronic pancreatitis has been reported in over 50% of diabetic cats. The use of amylase and lipase as an indicator of pancreatic disease in cats is ineffective. TLI for cats The use of Trypsin-like-immunoreactivity (TLI) has been shown to be a sensitive indicator of pancreatic disease in cats. The use of diluted insulin can improve dosage accuracy and aid absorption so improving control. Test - Fructosamine Sample = Serum Code - FRUC Charge - £9.50 Test - Feline TLI Sample - Serum Code - TLIF Charge - £25.00 Allow 10 days Back Performing a Glucose CurveAdmit the patient as early in the day as possible. Insulin is administered and meals offered at the usual times and samples for blood glucose are taken every two hours for 18-24 hours. You may need to alter the sample interval during the night (4hrs) but the result will be more useful if you can keep as near to 2 hours as possible
Test - Glucose Curve Up to 12 x Glucose Sample - Up to 12 Oxalate fluoride plasma Code - GC Charge - £16.00 Back Feline Hyper-thyroidism - which test ?Most hyperthyroid cats have increased levels of T4. However it is not uncommon to report a T4 result within the reference range from a cat with suspected hyperthyroidism, based on the presence of a palpable thyroid gland. Not all palpable thyroid glands are associated with hyperthyroidism of course.It is possible that the cat may still be in an euthyroid state and that hyperthyroidism is yet to occur. It is also possible that due to concurrent non-thyroidal disease there is a suppression of T4. In any of these situations you should consider re-testing the sample using a more appropriate test. Test of Choice The test of choice for further investigating hyperthyroidism in cats is Free T4 using the equilibrium dialysis method (FT4D). In a recent in-house trial more than 50 % of samples from cats in the above categories with Total T4 results within the reference range showed elevated Free T4D results. It should be noted that there have been reports that a small number of cats with non-thyroidal illness may show increased FT4D. However it is our belief that even if this is the case the test still clarifies a significant proportion of suspect hyperthyroid cases. Test - Free T4 by Equilibrium Dialysis Sample - Serum only Code - FT4D Charge - £23.00 Back Canine Hypo-thyroidism - which test ?Hypothyroidism is a common condition in dogs. The gradual onset and clinical complications associated with the condition can make definitive diagnosis difficult. The situation is not helped by the changing fashion for an appropriate diagnostic test. There does however seem to be a consensus of opinion as to the appropriateness of the test options available.TSH Stimulation The TSH stimulation test is still considered to be the most sensitive test, least affected by concurrent non-thyroidal illness and other interfering factors. The problem is TSH is not readily available and it is not licensed for use in the UK. The material is of variable potency and given the bovine origins the potential BSE risk has to be considered. An additional potential problem is the risk of anaphylaxis from the injection of TSH. Total T4 The measurement of Total T4 is considered to be a useful low cost screening test. Total T4 is reduced in 95 % of dogs with hypothyroidism but the test is subject to a variety of interference factors. Free T4 by equilibrium dialysis Dogs with symptoms of hyperthyroidism and a T4 in the reference range should have their Free T4 checked using the equilibrium dialysis method (FT4D). In this test the active T4 component is extracted from the serum by dialysis. This removes the interfering factors, allowing a very accurate determination of Free T4 using a sensitive radio-immunoassay technique. The technique is time consuming and as a result more expensive than a Total T4 determination but it does have the advantage of increased accuracy and is less affected by interference such as non-thyroidal illness, current drug therapy and thyroid autoantibodies. Back UpdatesAspergillus Test................The test period for the Aspergillus fumigatus AGP test has been increased from 7 to 10 days, to increase the sensitivity of the test. Please allow for a corresponding delay in reporting the results. Amendment Notice
Inject i/v 0.32 microg (µg) Buserelin (Receptal, Hoechst).Due to a misprint the original version showed the dose in milligrams not micrograms. Copies of the amended page are available on request. Print - Test Protocol No 8 - The Detection of Ovarian Activity Testing for Vaccination Immunity
Tail EndSmall Pox Virus to stayThe WHO has granted the Small Pox virus a last minute reprieve. The increased fear of bio-terrorism has prompted the US to delay plans to destroy remaining stocks of the virus. The WHO has appointed a new scientific panel to decide what research is still needed to develop vaccines and anti-viral drugs. The panel has until 2002 to set another final date for destruction. The stocks were due to be destroyed in 1993 and again in 1995, but each time scientists have pleaded that they need to continue with their studies of the virus. (This Week 1.5.99 p12) Back |
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