Patient's question:
Male, 60 years old, urinates 7 times a day, approximately 3500 milliliters, with excessive foam. He previously had high blood sugar, which returned to normal after treatment. Blood sugar, urinalysis, and renal function tests are all normal. What could be the issue? Is it necessary to undergo further tests?Doctor's answer:
Hello:According to the pathological and physiological classification of polyuria, it can be divided into two major categories:
(1) Hypertonic polyuria: Urine specific gravity is above 1.020, and urine osmolality significantly exceeds plasma osmolality. It can be caused by excessive glucose excretion (diabetes), excessive urea excretion (high-protein diet, high-calorie enteral feeding), or excessive sodium excretion (chronic adrenal cortical insufficiency).
(2) Hypotonic polyuria: Urine specific gravity is below 1.005, and urine osmolality significantly plasma osmolality. It is further divided into two types: vasopressin-resistant polyuria and vasopressin-sensitive polyuria. The former is caused by renal lesions and is seen in chronic interstitial nephritis of various causes, hypokalemic nephropathy (primary aldosteronism, chronic diarrhea, etc.), hypercalcemic nephropathy (hyperparathyroidism, etc.), hyperuricemia, Sj?gren's syndrome, polycystic kidney disease, and nephrogenic diabetes insipidus. The latter is seen in diabetes insipidus and polyuria caused by excessive thirst and drinking.
Differential diagnosis should focus on the following four points: ① First, distinguish between hypertonic or hypotonic polyuria by measuring urine specific gravity, urine osmolality, and plasma osmolality; ② For osmotic polyuria, measure fasting blood glucose, blood and urine sodium, blood and urine urea, etc., to determine the type of solute causing hypertonic diuresis. Based on medical history and a detailed physical examination, the etiology can be identified; ③ For hypotonic polyuria, water deprivation test, hypertonic saline test, and vasopressin test can be performed to determine whether the polyuria is renal, psychiatric, or central in origin; ④ For renal polyuria, medical history, physical examination, and laboratory tests such as renal function, serum potassium, serum calcium, and blood uric acid can be used.