The Review Course in Family Medicine
Kidney Stones - Even with Time, Not Everything Passes
by Dr. Chinmay Dalal MD CCFP
Any one of these could be an excellent SAMP question about Nephrolithiasis!
Does the composition of the stone actually matter?
YES! Not just for dietary consideration after, but for imaging as well as response to treatment.
Usual Suspects - Previous stones, family history of stones, increased calcium (↑ in diet or diseases causing changes in minerals (ie Hyperparathyroidism = increase Ca))
Malabsorption (eg, gastric bypass procedures, bariatric surgery, short bowel syndrome)
Associated with patients with diabetes, obesity, gout, hypertension, and pregnancy
Hematuria - Present in approx 90% of cases - Absent in approx 10-30% of cases THEREFORE not good enough to rule out if negative!
Back pain (especially unilateral) - Intermittent/Paroxysmal - lasting 20-60min at a time - Ranges from very little to legitimate 10/10 pain (not hangnail 10/10 pain!) Associated with nausea/vomiting/abdominal pain and urinary urgency/dysuria
Diagnosis: CT KUB vs XR KUB vs US vs intravenous pyelogram (IVP)?!?
X-ray Kidney, Ureter, Bladder (KUB) - Pro: Less radiation (0.8mSv or 8 Chest XRays worth of radiation) - Con: Less sensitive than CT, can’t see hydronephrosis
CT KUB Note: Choosing Wisely has recommended avoiding CT in some recurrent episodes. - Pro: Preferred (most sensitive), can see hydronephrosis, can see other stones in kidney if present - Con: High dose of radiation that other modalities (though less than a normal CT Abdo/Pelvis) thus not recommended in pregnancy - In general terms; uric acid, cystine, and struvite stones can usually be distinguished from calcium oxalate calculi (but not the different types of calcium oxalate)
US - Pro: No associated radiation, can see hydronephrosis, can do as point of care beside - Con: Not as sensitive as CT KUB, not as good at size estimation/composition
IVP: Imaging of KUB before and after administration of IV Contrast - Pro: Sees hydronephrosis - Con: Less sensitive and less specific than CT KUB but almost similar about or radiation to low dose CT KUB
Always add a UA to the testing, it’s cheap and very sensitive - Though this gets progressively less sensitive as the days go by after initial pain (ie Day 3 after pain starts, neg microscopic/gross hematuria much less sensitive than Day 1 neg hematuria)
Pain: NSAIDS are especially useful as they can concentrate in the kidneys and the ureter (targeted pain control) - Though initial opioids and parenteral control is absolutely acceptable for this as the time to onset is faster
Expulsion: - Alpha blockers (ie. Tamsulosin) - Increased Hydration - Straining (Aids in prevention of next stone)
When to Refer:
Stone >10mm (spontaneous passage becomes less likely as the size increases above 4mm)
Stone not passing with conservative management
Photo Credit: dfaulder, https://www.flickr.com/photos/dfaulder/5507761641