Polyuria

Rationale

Polyuria, defined as high urine output, may be confused with urinary frequency, which refers to needing to urinate more often than usual. Urinary frequency is encountered more often in clinical practice. Although less common, polyuria may be the presenting symptom of a potentially serious underlying condition.

Causal Conditions

(list not exhaustive)

1. Water diuresis
   1. Excessive intake (polydipsia)
   2. Excessive loss – diabetes insipidus: central versus nephrogenic (arginine vasopressin [AVP] deficiency versus AVP resistance)
2. Osmotic diuresis
   1. Sugar – diabetes mellitus
   2. Urea – chronic renal disease
   3. Salts – organic anions

Key Objectives

Given a patient who presents with polyuria, the candidate will diagnose the cause, severity, and complications, and will initiate an appropriate management plan.

Enabling objectives

Given a patient with polyuria, the candidate will

1. list and interpret critical clinical findings, including those derived from
   1. diagnosing polyuria, identifying causal factors and severity, and differentiating polyuria from urinary frequency,
   2. inquiring about any personal or family history of diabetes, and
   3. identifying neurological features that may suggest intracranial pathology as a cause of central diabetes insipidus;
2. list critical investigations and interpret their results, including
   1. tests that distinguish between water and osmotic diuresis,
   2. screening for diabetes, and
   3. the patient’s voiding diary when appropriate;
3. construct an effective initial management plan, including
   1. managing the underlying cause, and
   2. determining whether the patient requires specialized care.