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At initial eval for known kidney/ureteral stones
Medical, diet, family hx - Hx medical [CP]: obesity, hyperthyroid, gout, RTA type 1, DM type 2, bone dz, 1° HPT, malabsorption,1 stone-provoking meds/OTCs2
- Hx diet [CP]: ↓ fluid intake, beverage type (cola), ↑/↓ Ca++ intake, ↑ Na+ intake, ↓ fruit/veg, ↑ animal purines, ↑ oxalate foods
Lab/imaging - Lab: BMP, Ca++, uric acid, UA dipstick + micro [CP].3 Urine cx if UA suggests UTI, or if hx recurrent UTI.
- If 1° HPT suspected (high/high-NL serum Ca++):4 intact PTH level [CP]
- If recurrence or pt high-risk5/interested 1st-stone former: additional metabolic tests [S/B] including one to two 24-hr urines on random diet:6 total volume, pH, Ca++, oxalate,7 uric acid, citrate, Na+, K+, Cr [EO]
- If stone available: analyze stone at least once [CP]
- Review imaging studies to quantify stone burden8 [CP]
Footnotes 1 Malabsorptive GI states associated w/ stone dz: bowel resection, bariatric surgery, bowel/pancreatic dz.
2 Stone-provoking meds: probenecid, some protease inhibitors, lipase inhibitors, triamterene, chemo, vit C, vit D, Ca++, CAIs (topiramate, acetazolamide, zonisamide).
3 If urine pH >7 or urea-splitting organisms (e.g., Proteus): struvite stones possible.
4 Suspicion may also arise w/ predominantly Ca++ phosphate stones w/ ↑ urinary Ca++, or mid-range PTH in face of higher serum Ca++. Measuring vit D levels may help, as low D may mask 1° HPT, or contribute to 2° HPT.
5 High risk = (+)FHx, malabsorptive dz, recurrent UTI, obesity, medical dz (RTA type 1, 1° HPT, gout, DM type 2), solitary kidney.
6 Do not perform “fast and calcium load” testing to distinguish hypercalciuria type [R/C].
7 Suspect 1° hyperoxaluria if urinary oxalate excretion >75 mg/day in adults w/o bowel dysfxn (refer for genetic test/specialized urine tests).
8 Multiple/BL renal calculi @ initial presentation may signal ↑ recurrence risk. Nephrocalcinosis implies metabolic dz (RTA type 1, 1° HPT, 1° hyperoxaluria) or anatomic dz (medullary sponge kidney).
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Follow-up after tx initiation
Obtain a single 24-hr urine panel9 for stone risk factors - Within 6 mo after tx initiation, to assess tx response [EO]
- At least annually, depending on stone activity [EO]. If stone-free on tx for extended period, consider d/c follow-up tests.
Additional labs - Periodic blood tests for ADRs10 in pts on drug tx [S/A]
- Repeat stone analysis, when available, esp. if not responding to tx [EO]
- If struvite stone: monitor w/ urine cx for re-infxn w/ urease-producing organisms [EO]
Imaging - Periodic F/U studies (plain film, renal US, or low-dose CT)11 to assess stone growth/formation, based on stone activity [EO]. 1-yr interval recommended for stable pts, tailor clinically.
Footnotes 9 Tailored testing may be considered (eg, pure uric acid stones: check urine pH, uric acid, Cr; Ca++ stones: expanded panel). Check for relevant change in urinary Ca++, oxalate, uric acid, cystine excretion, pH, and increased urinary volume, citrate excretion. Urinary stone-forming salt super-sat is part of many 24-hr urine panels. Urine K+ can gauge med compliance. Animal protein intake markers (urine urea nitrogen, urinary sulfate) can be used to assess diet. Measure urinary cystine if cysteine stones or FHx cystinuria. Suspect 1° hyperoxaluria if urinary oxalate excretion >75 mg/day in adults w/o bowel dysfxn (refer for genetic test/specialized urine tests).
10 ADRs: hypokalemia, glucose intolerance, ↑ liver enzymes, anemia/hematologic abnl, hypercalcemia, etc., depending on drug.
11 Plain films acceptable for radiopaque stones: limited radiation, lower cost, but not as sensitive/specific as CT. Renal US preferred for most pts w/ radiolucent stone: no ionizing radiation, less costly, but not as sensitive/specific as CT. Unenhanced CT is most sensitive; can often be done w/ low-dose protocol.
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