Investigations to detect the causes of urinary stone formation

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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Stones in kidneys, ureter and urinary bladder
Symptoms of urinary stones
Investigations and treatment of urinary stones
Investigation to detect the causes of urinary stones
How to prevent urinary stone formation

Stones in the kidneys, ureters and urinary bladder – Types and causes

Renal and urinary bladder stones (calculi)

Urinary stone is a fairly common throughout the world particularly in the Middle East. Most urinary stones are composed of calcium oxalate and phosphate; these are more common in men. Mixed infective stones, which account for about 15% of all calculi, are twice as common in women as in men. The overall male to female ratio of stone disease is 2 :1. Stone disease is frequently a recurrent problem. More than 50%of patients with a history of nephrolithiasis will develop a recurrence within 10 years. The risk of recurrence increases if a metabolic or other abnormality predisposing to stone formation is present and is not modified by treatment.


Composition of urinary stones

Calcium oxalate usually with calcium phosphate - 65%
Calcium phosphate alone – 15%
Magnesium ammonium phosphate (struvite) -10-15%
Uric acid 3-5%
Cystine 1-2%




How urinary stone is formed?

Inhibitors of crystal formation are present in normal urine preventing the formation of stones, as the concentrations of stone-forming substances exceed their maximum solubility in water. Many stone-formers have no detectable metabolic defect, although microscopy of warm, freshly passed urine reveals both more and larger calcium oxalate crystals than are found in normal subjects. Factors predisposing to stone formation in these so-called 'idiopathic stone-formers' are:

#chemical composition of urine that favors stone crystallization
#production of a concentrated urine as a consequence of dehydration associated with life in a hot climate or work in a hot environment
#impairment of inhibitors that prevent crystallization in normal urine.


Causes of urinary stone formation:

Hypercalcaemia
If the GFR is normal, hypercalcaemia almost invariablyleads to hypercalciuria. The common causes of hypercalcaemia leading to stone formation are:

primary hyperparathyroidism
vitamin D ingestion
sarcoidosis.

The other causes of stone formation are:

Dehydration
Hypercalciuria
Hyperoxaluria
Hyperuricaemia and
hyperuricosurea
Infection
Cystinuria
Renal tubular acidosis
Primary renal disease(polycystic kidneys, medullary sponge kidneys)
Drugs

Causes of Urinary stone formations
Symptoms of urinary stones
Investigations and treatment of urinary stones