What tests are appropriate in the diagnosis of kidney stones?
Perform a complete urinalysis with focus on pH, hematuria, pyuria, bacteriuria, and crystalluria. If pH is high or there is bacteriuria, order a urine culture. Perform appropriate radiographic studies (see question 34). Have the patient strain all urine and save the stone, if passed, for stone analysis. If this is the patient’s first stone, the pain subsides, and the stone is < 5 mm in diameter, conservative management with follow-up for several months is acceptable. Greater than 50% of stones in the proximal ureter and 75% of stones in the distal ureter < 5 mm in diameter pass spontaneously. Order vitamin D and a blood chemistry panel that includes serum sodium, potassium, chloride, carbon dioxide, creatinine, calcium, albumin, phosphorus, magnesium, and uric acid. Consider measurements of serum PTH and random urine for determination of the Ca/Cr ratio. If the patient has continued symptoms, if the stone is > 5 mm in diameter, or if obstruction is present, consult a urologist and plan for a more extensive evaluation. Include a 24-hour urine test for creatinine, sodium, calcium, phosphorus, magnesium, oxalate, citrate, uric acid, and urinary supersaturation. A 24-hour urine collection is adequate if creatinine is 15 to 20 mg/kg in men and 10 to 15 mg/kg in women. Consider repeating the 24-hour urine test to focus on abnormalities 6 weeks after medical intervention. Discontinue multivitamins 5 days before collection to avoid antioxidant effects.
