Kidney Stones (Nephrolithiasis / Urolithiasis)

Clinic A/P, adults, Hospital A/P, Adults

Workup of nephrolithiasis (kidney stones)

  • CT without contrast. Get a non-contrast helical CT – ureteral dilation without stone suggests recent passage. A non-contrast CT is  97% sensitive and 95% specific for the diagnosis of urolithiasis.
  • U/A & UCx
  • CMP (electrolytes, BUN/Cr, Ca), phosphate (PO4), PTH
  • Strain urine for stones to analyze.
  • 24-hour urine x2 (>6wk after acute setting) for calcium, phosphate (PO4), oxalate, citrate, sodium, creatinine, PH, potassium, and volume.

Acute Treatment of Kidney Stones (Nephrolithiasis)

  • Pain mgt: NSAIDS as effective as opioids. Combining both is superior.
  • Hydration, drink lots of water. IVFs if admitted.
  • Tamsulosin 0.4mg PO daily for four weeks helps to pass stones 4mm to 10mm in size. Stones above 10mm need intervention to pass. Consult urology. Stones <4mm don’t need tamsulosin and it is not better than placebo in those small stones.
  • Antibiotics if the patient has UTI
  • Consult urology immediately if the patient has an obstruction (especially if he has only one kidney), sepsis 2/2 to UTI, significant AKI, intractable pain, nausea, and vomiting.
  • Urology may perform lithotripsy, stent, percutaneous nephrostomy, or ureteroscopic removal of the stone.

*Tamsulosin is an alpha-blocker. It relaxes smooth muscle and improves urine flow. It is a peripherally-acting alpha-blocker. Alpha blockers are better than CCBs in promoting relaxation of the ureters to pass stones.

Prevention of kidney stones

  • Drink lots of water (>2 L/d) for a goal UOP of ≥ 2 L/d
  • Alkalinization of urine if acidic stones: uric acid, cystine, oxalate stones. K-Citrate is used to alkalinize the urine.
  • Acidify urine if basic stones.
  • For struvite stones, give antibiotic to treat any UTIs.
  • The 24-hour urine collection x 2 (see workup above) will identify specific risk factors that you need to treat.

Treatment of recurrent kidney stones

In addition to doing the things under the prevention of kidney stones (above), patients with recurrent kidney stones benefit from the following.

  • Thiazide diuretic, citrate, or allopurinol is recommended if the fluid increase is not sufficient. Thiazides have been shown to decrease stone formation in patients with hypercalciuria.

When should you acidify urine (with cranberry juice or betaine.)?

Basic stones tend to form in basic environments and acidic stones tend to form in acidic environments.

Acidic stones: Uric acid stones, cystine (an amino acid), and calcium oxalate (oxalate = oxalic acid)
Basic stones: calcium phosphate (a basic salt like calcium carbonate), and Magnesium ammonium phosphate or struvite (also a basic salt).

Acidification of urine is indicated only for basic stones. Acidification turns the urine more acidic and basic stones find it difficult to form in an acidic environment. Basic stones form easily in a basic environment. So you would acidify urine for calcium phosphate and struvite (Magnesium ammonium phosphate) stones. Why? Again because these basic stones tend to form in alkaline urine. Acidifying urine prevents them from forming.

On the other hand, uric acid stones, cystine, and calcium oxalate stones tend to form in acidic urine. So acidifying urine is not indicated.

 

References / Further Reading

http://www.ajronline.org/doi/abs/10.2214/AJR.07.3414 (AJR 2008;191: 396-401)
http://www.aafp.org/afp/2011/1201/p1234.html  (AFP. 2011 Dec 1;84(11):1234-1242.)
Qaseem A, Dallas P, Forciea MA, et al: Dietary and pharmacologic management to prevent recurrent nephrolithiasis in adults: A clinical practice guideline from the American College of Physicians. Ann Intern Med 2014;161(9):659-667.
Hauk L: Prevention of recurrent nephrolithiasis: Dietary and pharmacologic options recommended by the ACP. Am Fam Physician 2015;92(4):311.
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