![]() ![]() It is therefore important to note that this test is contra-indicated in animals with renal failure. The purpose of this test is to determine whether a dog can concentrate its urine in response to dehydration, i.e., whether it can release ADH and whether the kidneys are able to respond to this hormone. If a diagnosis is still eluding the clinician, a water deprivation test should be performed. After a thorough review of all test results, a cause would either be found, or most causes would at least be ruled out. If hypercalcaemia is detected, further tests to find a neoplastic process might include thoracic radiographs, lymph node or bone marrow aspiration. Evaluation of the hypothalamic-pituitary-adrenal (HPA) axis with ACTH stimulation or low dose dexamethasone suppression testing should be performed if Cushing's disease is suspected. A biochemical profile which includes electrolytes can be highly suggestive of renal failure, hypercalcaemia, hypokalaemia, hyper/hypoadrenocorticism or hepatic disease.Ībdominal radiographs/ultrasound may be indicated to evaluate the liver, kidneys, adrenals and uterus. At this stage, many disorders would have been ruled out or made very unlikely by the signalment, history, clinical examination and urinalysis.Ī full blood count can increase the suspicion of pyometra or hyperadrenocorticism. Proteinuria, especially in the presence of dilute urine, indicates significant protein loss and could suggest glomerulonephritis.įrom here on, the clinician should perform the test that she thinks will yield the most information for the 'diagnostic currency' that the client provides. Urine culture should be considered, even when the urine sediment is unremarkable, as some cases of hyperadrenocorticism might have an impeded white cell response due to immunosuppression. Glucosuria significantly narrows the differential diagnoses. Hyposthenuric (SG <1.008) urine is indicative of diabetes insipidus (either central of nephrogenic) or primary polydipsia, but, importantly, imparts knowledge about the normality of the kidneys, i.e., it indicates that the renal tubules are able to actively dilute the glomerular filtrate and are thus functioning appropriately. The presence of constantly isosthenuric urine (SG 1.008-1.012) is highly suggestive of chronic renal failure. Primary polydipsia, in turn, is caused by certain behavioural or neurological disorders with prolonged intake of large amounts of water resulting in renal medullary washout and the production of large amounts of dilute (SG 1.030) makes PU/PD very unlikely. ![]() Primary polyuria is either due to osmotic (solute) diuresis, ADH (antidiuretic hormone) deficiency or renal insensitivity to ADH. Much less frequently, polydipsia is primary, with a compensatory polyuria to excrete the excess water load. In these cases, polydipsia represents a compensatory mechanism to maintain total body fluids within normal limits. Most disorders of water balance are due to the inability of the kidney to conserve water-termed primary polyuria. Pathophysiology of Disorders of Water Balance The balance between water loss and water intake results from interactions between the hypothalamus, the pituitary gland and the kidney, and is maintained by thirst and renal excretion of water and salt. Normal urine production is approximately 20-40 ml/kg/day or, put differently, 1-2 ml/kg/hour. Healthy dogs generally consume between 50-60 ml/kg/day depending on the moisture content of their diets, the ambient temperature and humidity and their level of activity. Polyuria is defined as a daily urine output of greater than 50 ml/kg per day, while polydipsia is defined as a fluid intake of more than 100 ml/kg/day. Polyuria and polydipsia (PU/PD) are frequent presenting complaints in small animal practice. ![]()
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