1/31/2024 0 Comments Normal specific gravity of urineIf the patient is dehydrated and renal function is normal, the urine SG should be greater than 1.030 (dog) or 1.035 (cat). If the urine SG is between 1.008 and 1.030 the first consideration is whether the urine is inappropriately dilute. If the urine is very dilute (hyposthenuria) there are a limited number of diagnostic possibilities and differentiation of the possible causes is relatively simple. Persistent polyuria (primary or secondary to polydipsia) or failure to concentrate urine appropriately in the presence of dehydration or azotaemia may be the result of a structural renal abnormality (i.e., primary-renal disease) or a functional renal abnormality (extra-renal disease).Ī functional (extra-renal) abnormality occurs when the kidney is structurally normal but urine concentration is impaired as a result of alterations in, for example, medullary hypertonicity (e.g., hyponatraemia) or ADH function (ADH deficiency, impaired ADH function secondary to hypercalcaemia). Note that most dehydrated cats with normally functioning kidneys will have a urine SG > 1.045. If an azotaemic animal has a urine SG less than these values then the patient must have impaired urine concentrating ability, because if the azotaemia was due to pre-renal factors only and the patient had normal renal concentrating ability, the urine SG would be >1.030 (dogs) or 1.035 (cats). If a dehydrated animal has a urine SG less than these values it has by definition inappropriate urine concentration and it must have some degree of renal dysfunction (primary structural renal dysfunction or extra-renal dysfunction). If an animal is dehydrated or hypovolaemic, the appropriate renal response is to produce urine that is concentrated to at least a SG of 1.030 (dogs) or 1.035 (cats). Always interpret urine SG in relation to the hydration status of the patient.Īlthough urine with a SG greater than 1.012 has been concentrated, the degree of concentration may not be appropriate. Normal animals may have a urine SG of any value depending on the physiological circumstances. Urine with an SG of 1.012 has been concentrated to some degree-however whether the degree of concentration is appropriate must now be determined for the patient If a patient has been confirmed as being polyuric and polydipsic and/or azotaemia has been identified, the initial and most important diagnostic step is to determine the urine specific gravity (SG)-without this information, appropriate interpretation of other pathology results can be difficult. Too often a patient with low urine SG and azotaemia is diagnosed as having renal failure-this is of course a very possible diagnosis especially in cats, but there are other disorders that impair both urine concentration and cause azotaemia that the practitioner must always consider. The interpretation of urine specific gravity (SG) and serum urea and creatinine requires an understanding of renal physiology and the mechanisms that control these parameters.
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