Diagnosis for Kidney Stones
Urinalysis and imaging are the primary methods of diagnosing kidney stones (calculi, plural; calculus, singular). Initial urinalysis is done in conjunction with a routine chemistry profile (metabolic profile) to identify elevations in serum calcium.
Urinalysis: both biochemical and microscopic evaluation of the urine is helpful in initiating a diagnosis of a stone before imaging confirms it. Microscopic findings include the presence of red blood cells and white blood cells in the urine. Biochemical evaluation, especially useful in those with recurrent stones, can identify calcium It will also indicate the acidity or alkalinity of the urine.
- PH >7 suggests calcium phosphate or struvite calculi (based on the finding of phosphate crystals), or cystine calculi (based on the finding of the characteristic hexagonal crystals seen in cystinuria).
- PH < 5 (acidic) can decrease the solubility of uric acid, leading to crystallization out of solution (urine) of uric acid (as uric acid stones).
The radiopacity (ability to stand out on X-ray) of stones makes them readily identifiable. Occult stones can be diagnoses as a cause of mysteriously recurrent urinary tract infections in spite of appropriate antibiotic management.
Intravenous pyelogram, using dye to visualize the urinary system, from kidneys to bladder, are helpful in identifying where non-migrating stones are.
Patients should be instructed to strain their urine so that any stones or stone fragments can be submitted for examination.