In an elderly patient who has had a single incident with one stone, only restricted investigation is necessary. Younger patients and those with recurring stone formation necessitate detailed investigation.
Following are the investigations done to find out the causes urinary stone formation.
Renal imaging is required to define the presence of a primary renal disease predisposing to stone formation.
Urine culture to detect significant bacteriuria may point to mixed infective stone development, but relapsing bacteriuria may be an effect of stone formation rather than the original source.
Chemical analysis of any stone passed may be of immense value and all that is necessary in the diagnosis of cystinuria or uric acid stone formation.
Serum calcium concentration should be measured and corrected for serum albumin concentration. Hypercalcaemia (High blood calcium level), if present, should be investigated further for hyperparathyroidism.
Serum urate concentration is usually, but not always, elevated in uric acid stone-formers.
A screening test for cystinuria should be done by adding sodium nitroprusside to a random unacidified urine sample; a purple color indicates that cystinuria may be present. Urine chromatography is necessary to identify the diagnosis precisely.
Urinary calcium, oxalate and uric acid output should be measured in two successive cautiously collected 24- hour urine samples. After withdrawing aliquots for measurement of uric acid, it is required to add acid to the urine in order to prevent crystallization of calcium salts upon the walls of the collection vessel, which would give falsely low reports for urinary calcium and oxalate.
Plasma bicarbonate is low in renal tubular acidosis. The report of a urine pH that does not dip below 5.5 in the face of metabolic acidosis is diagnostic of this condition.
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Symptoms of urinary stones
Investigations and treatment of urinary stones
Investigation to detect the causes of urinary stones
How to prevent urinary stone formation
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