Harper et al identified risk factors for stone formation in patients with a renal transplant. The absence of innervation in the transplanted kidney may mask clinical signs of stone disease and subsequent infection. The authors are from St Peter's and Middlesex Hospitals in London.


Risk factors:

(1) low urine volumes, with a concentrated and alkaline urine

(2) urinary tract infection

(3) low urinary citrate excretion

(4) presence of crystals (crystalluria) in a fresh urine samples at 37°C

(5) elevated urine calcium excretion, often associated with hypercalcemia

(6) elevated urinary uric acid excretion

(7) renal tubular acidosis


Other findings associated with stone formation:

(1) urinary excretion of magnesium at the lower limit of normal

(2) urinary excretion of phosphate at the lower limit of normal


Therapeutic interventions to reduce stone formation:

(1) maintain a high fluid intake to promote urine output

(2) suppression of urinary tract infections

(3) administration of potassium citrate


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