Polyuria and Polydipsia (Case 38)

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Chapter 46
Polyuria and Polydipsia (Case 38)

Kavita Iyengar MD

Case: The patient is a 68-year-old woman with a medical history of hypertension, hyperlipidemia, and obesity. She presents to the outpatient office because for the last few weeks she has been more tired than usual and feels that she has been drinking more water. She has also been going to the bathroom more frequently, particularly at night. In addition, she has blurry vision and headaches. Her husband is also your patient. He has trouble maintaining control over his blood sugar and is also obese. Both the patient and her husband often miss scheduled follow-up appointments.

The patient’s medications are hydrochlorothiazide, atorvastatin, and an aspirin. Her father had hypertension and coronary artery disease, and her mother was recently diagnosed with type 2 diabetes mellitus. The patient works as an administrative assistant. She smokes half a pack of cigarettes a day and drinks a glass of wine occasionally.

On examination she is pleasant and conversant and appears comfortable. She states that she thinks she may have “a little sugar” like her husband. Her vital signs are within normal limits, but her body mass index (BMI) is 37. Her lungs are clear to auscultation, and heart sounds are normal. Her abdomen is obese. Her neurologic exam is normal except for a decreased monofilament sensation in her feet.

Differential Diagnosis

Diabetes mellitus, type 1

Diabetes mellitus, type 2

Diabetes insipidus (DI)

Hypercalcemia

Gestational diabetes

 

Speaking Intelligently

Polyuria is most often caused when the kidneys are subjected to an increased osmotic load, such as that from glucose or calcium. Alternatively, it may be due to endocrine disorders of fluid regulation such as vasopressin (antidiuretic hormone, ADH) deficiency. Conditions that cause bladder irritability or obstruction such as cystitis or prostatic enlargement can cause increased urinary frequency, but usually not polyuria. When most clinicians are assessing an obese patient with polyuria and polydipsia, type 2 diabetes mellitus, which affects over 20 million persons in the United States, is the first diagnosis that comes to mind. A point-of-care capillary glucose by finger-stick or a urinalysis can quickly make the diagnosis of uncontrolled diabetes, so that this patient can quickly get the appropriate care.

PATIENT CARE

Clinical Thinking

• Diabetes mellitus is diagnosed with two fasting blood glucose measurements greater than 125 mg/dL or a random value greater than 200 mg/dL in a patient with symptoms. At this point, you have to determine how sick the patient is and whether the patient needs inpatient management to treat symptomatic hyperglycemia or has life-threatening complications such as diabetic ketoacidosis (DKA) or a nonketotic hyperosmolar state.

• Patients with type 1 diabetes may present to the emergency department in DKA, with an elevated blood glucose, or an anion gap metabolic acidosis with positive serum ketones and electrolyte imbalances.

• Patients with type 2 diabetes may present in a hyperosmolar state with severe volume depletion, hypernatremia, and very high blood glucose levels.

• If the glucose and calcium are normal, other conditions such as DI or primary polydipsia should be considered.

History

• Hyperglycemia can present as a spectrum from one in which the patient is completely asymptomatic to one in which the patient has DKA or a hyperosmolar state.

• In an asymptomatic patient, hyperglycemia may be an incidental finding on laboratory work done for other reasons, or it could be seen in a patient admitted to the hospital in acute stress (e.g., from a myocardial infarction or severe infection). At times, medications such as corticosteroids can be the cause.

• If a patient’s blood glucose has been consistently high for some time, symptoms such as polydipsia, polyuria, and nocturia can be seen, since excess glucose delivered to the kidneys causes an osmotic diuresis. Hyperglycemia can also manifest as blurry vision from the effects of glucose on the lens, or tingling and numbness in the toes from peripheral neuropathy. Other symptoms that should be sought are weight loss and fatigue.

• A patient who presents in DKA or a hyperosmolar state may be too sick to give a history but may have an obvious inciting insult such as infection or a myocardial infarction. Nausea, vomiting, and abdominal pain are common symptoms in patients with DKA.

• A family history of diabetes can be found, which is more common in patients with type 2 diabetes.

• Patients with DI may have pituitary tumors; they should be questioned about headaches and visual changes, and other endocrinopathies. Patients with primary polydipsia may be drinking excessive amounts of water because of a psychiatric or central nervous system (CNS) disorder.

Physical Examination

• Look for signs of complications of long-standing hyperglycemia.

• Patients with type 2 diabetes are typically overweight, while those with type 1 diabetes are often not.

• An exam of the skin may reveal signs of insulin resistance such as acanthosis nigricans and skin tags.

• Patients with type 1 diabetes may have other signs of autoimmune disorders such as vitiligo and goiter.

• Screening for chronic complications of diabetes should include a monofilament exam looking for sensory neuropathy, a foot exam assessing for peripheral vascular disease, and a dilated funduscopic exam screening for retinopathy.

• In a patient admitted to the hospital with DKA, Kussmaul respirations and ketotic breath may be noted; very sick patients may present with mental status changes and signs of volume depletion such as hypotension and tachycardia.

Tests for Consideration

Fasting plasma glucose: Obtained to diagnose diabetes.
A value of 100 to 125 mg/dL indicates pre-diabetes, while a value above 125 mg/dL obtained twice indicates diabetes.

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Random plasma glucose: Can also be used to diagnose diabetes. A value of 140 to 200 mg/dL indicates pre-diabetes or glucose intolerance, while a value above 200 mg/dL, in the presence of symptoms, is diagnostic of diabetes.

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Fingerstick blood glucose: Checked by the patient at home, using a glucometer. This should typically be checked once daily in patients on oral hypoglycemic agents and three to four times a day in patients on insulin. This could also be checked in an emergency, while awaiting serum blood glucose values from the lab.

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Hemoglobin A1c (HbA1c or glycosylated hemoglobin): Gives an idea of the average blood glucose over the 3- to 4-month period before the blood sample is drawn. The average blood sugar of a normal person should be less than 120 mg/dL, which corresponds to an HbA1c of 6%. For every point increase in HbA1c, a 30-point increase in the average blood glucose can be expected. For example, an HbA1c of 8% would suggest the patient’s blood glucose averaged 180 mg/dL over the previous 3 months. An HbA1c of less than 7% suggests good blood sugar control.

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Urine microalbumin-to-creatinine ratio: Elevated in early diabetic nephropathy.

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Serum creatinine: Elevated in later stages of diabetic nephropathy.

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Arterial blood gas and serum ketones: Used to assess patients with DKA in which an anion gap metabolic acidosis (pH < 7.30) and positive serum ketones are seen.

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Sodium: The osmotic effect of hyperglycemia can shift water from the extravascular to the intravascular space, which is measured as hyponatremia. This is particularly evident in the hyperosmolar state. As a general rule, for each 100 mg/dL of glucose over 100 mg/dL, the serum sodium concentration is lowered by approximately 1.6 mEq/L. Conversely, when glucose levels fall, the serum sodium level rises by a corresponding amount.

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Urine and serum osmolality: Patients who have lost excessive free water because of hyperglycemia or hypercalcemia will have high serum osmolality. Patients with DI usually have high serum osmolality and low urine osmolality. Patients with primary polydipsia will have normal or even low serum osmolality and appropriately dilute urine.

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Potassium: