Renal threshold: When blood glucose rises over a certain level, it spills into the urine.
Polyuria: Glucose cannot leave the body by itself--it must take water with it. Losing too much water means the body tries replacing it and this causes thirst, or polydipsia. When too much water is lost through excess urination and the excess drinking cannot make up for it, dehydration can occur.
Polyuria [pah-lee-YOOR-ee-ah], abbreviated as PU, is excessive urination and may be a sign of diabetes. Proper treatment with insulin and in unusual cases, oral medications, restores proper metabolic function and eliminates the symptoms. Polyuria can also be a signal of other diseases or bodily problems [1][2][3], including urinary tract infections. [4][5]
Polyuria in diabetes shows that the body is unable to metabolize carbohydrates properly. Carbohydrates are turned into glucose, which is sent into the blood to feed the cells. The cells, lacking insulin, can't accept the glucose, so it remains in the blood causing hyperglycemia. The extra glucose in the blood accumulates there until the kidneys see it as an impurity to be filtered out and discarded. This point is known as the renal threshold.
When the renal threshold is exceeded, and the excess glucose begins to spill into the urinary tract, the glucose makes the urine attract water in what's known as the osmotic effect. This extra water in the urine causes the excessive urination, dehydrating the body, which in turn causes the excessive drinking of polydipsia.
The blood, losing water, becomes more concentrated, leading to worse hyperglycemia and completing the vicious circle.
The over-frequent urination also takes with it electrolytes [11] which the body needs to keep itself going--sodium (salt) [12] and potassium [13] among them. This contributes to lethargy and weakness, as the body is not able to keep itself in balance without the proper amounts of electrolytes. [14] Loss of sufficient electrolytes is why many pets and people need intravenous fluids when suffering from DKA; these elements need to be replenished after being so severely depleted.[15]
Specific Gravity[]
The concentration (or lack of it) is determined by what's called a urine specific gravity test. The basis for comparison used is the specific gravity of water, which is 1.000. The specific gravity of urine which has a large amount of glucose (such as the urine of a yet to be controlled diabetic) increases by 0.010 units due to the amount of glucose present in it. [5][16]
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More information on this is found at urination. 
References[]
- ↑ Frequent Urination. Pet Education.com.
- ↑ Nelson, Richard (2002). Polyuria, Polydipsia & Diabetes Insipidus. WSAVA.
- ↑ Richards, Mike. Increased Drinking and urinating. Richards, Mike-Vet Info4Dogs.
- ↑ Diabetes Mellitus. Petplace.com.
- ↑ 5.0 5.1 Lunn, Katharine F., James Katherine M. (2007). Normal and Abnormal Water Balance: Polyuria and Polydipsia. Compendium.
- ↑ Laboratory informaion. Animal Emergency center of Milwaukee, WI.
- ↑ Vetsulin-Page 5. Intervet.
- ↑ Diabetes mellitus. Merck Veterinary Manual.
- ↑ Vetsulin Reference manual-Page 15. Intervet.
- ↑ Blood Glucose Converter. Children With Diabetes.
- ↑ Stoeppler, Melissa Conrad. What Are Electrolytes?. MedicineNet.
- ↑ Sodium & Chloride Requirements & Deficiencies. Pet Education.com.
- ↑ Potassium Requirements & Deficiencies. Pet Education.com.
- ↑ Diabetes. Long Beach Animal Hospital.
- ↑ Wortinger, Ann (February 2001). Electrolytes, Fluids and the Acid-Base Balance. Veterinary Technician.
- ↑ Specific Gravity of Urine. Cornell University.
- ↑ Polydipsia & Polyuria. Petplace.com.
- ↑ Pounds to Kilograms/Kilograms to Pounds online converter. Open Toronto.
- ↑ Polydipsia & Polyuria. Petplace.com.
More Information[]
- Urine Volume and Specific Gravity Merck Veterinary Manual
- Logical Approach to Polyuria and Polydipsia Church, David B., 2009, WSAVA
- Polyuria ProVet UK
- Polydipsia and Polyuria Washington State University
- Study Case — A Mixed Breed Dog with Elevated Blood Glucose and PU/PD Stortz, James P., et. al., 2005, University of Georgia
- The Diagnostic Approach to Polyuria in the Dog Kooistra, Hans S., 2010, WSAVA
- Vasopressin Response to Osmotic Stimulation in 18 Young Dogs with Polyuria and Polydipsia van Vonderen, Ilse K., Kooistra, Hans S., Sprang, Elpetra P.M., Rijnberk, Ad, Meji, Björn P., 2004, Journal of Veterinary Internal Medicine