Which of the following will be most likely associated with a staghorn calculus in kidney:
|B||Increased excretion of uric acid in urine|
|C||A positive dipstick test for sugar in urine|
|D||An alkaline urine pH|
a. Infection stones are composed primarily of magnesium ammonium phosphate hexahydrate (MgNH4PO4 • 6H2O) but may in addition contain calcium phosphate in the form of carbonate apatite (Ca10[PO4]6 • CO3).
b. Struvite stones (magnesium ammonium phosphate) occur only in association with urinary infection by urea-splitting bacteria.
a. The process of urealysis provides an alkaline urinary environment and sufficient concentrations of carbonate and ammonia to induce the formation of infection stones.
b. Because urease is not present in sterile human urine, infection with urease-producing bacteria is a prerequisite for the formation of infection stones.
c. The alkaline urine that results from this reaction (pH 7.2 to 8.0) favors the formation of ammonium:
i. NH3 + H2O ➙NH4+ + OH- pK = 9.0
d. Under physiologic conditions, the alkaline urine would prevent further generation of further ammonium.
e. However, in the presence of urease, ammonia continues to be produced despite alkaline urine, further increasing urinary pH. The alkaline environment also promotes the stone formation.