The nurse suspects that a client with polyuria is experiencing water diuresis. Which laboratory value suggests water diuresis?
A. High urine specific gravity
B. High urine osmolarity
C. Normal to low urine specific gravity
D. Elevated urine pH
Correct Answer: C. Normal to low urine specific gravity
Water diuresis causes low urine specific gravity, low urine osmolarity, and a normal to elevated serum sodium level. Water diuresis was accompanied by (i) a rapid increase in urea excretion during the phase of increasing urine flow, followed by a fall in later periods to values similar to those in non-diuresis, (ii) a slower increase in sodium output, continuing after the establishment of the constant water load, (iii) unchanged potassium excretion, but slightly increased ammonium outputs.
Option A: High specific gravity indicates dehydration. Hypernatremia signals acidosis and shock. In water diuresis, some of the changes in solute excretion may similarly result from altered tubular reabsorption, perhaps influenced by suppression of antidiuretic hormone (A.D.H.). In addition, the slower changes in sodium output may be related to several consequences of changes in body fluid volume.
Option B: Mannitol diuresis was accompanied by (i) a rapid increase in urea outputs which subsequently fell but remained significantly higher, (ii) a steep rise in sodium and potassium outputs to values that remained far higher than those in non-diuretic and water diuretic animals.
Option D: Elevated urine pH can result from potassium deficiency, a high-protein diet, or uncontrolled diabetes. The changes in mannitol diuresis are considered to result mainly from decreased tubular reabsorption, due to the lowered intraluminal sodium, potassium, and urea concentrations and increased intratubular fluid flow. Some of the acute increase in urea excretion may be due to washout of medullary urea into the tubular fluid.
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