A 60-year-old woman comes to the emergency department due to left flank pain and hematuria. Medical history is significant for recurrent urinary tract infections and hypothyroidism. Blood pressure is 130/80 mm Hg and pulse is 80/min. Physical examination shows left flank tenderness. CT scan of the abdomen is shown below: Urinalysis for this patient would most likely show which of the following?

Question

A 60-year-old woman comes to the emergency department due to left flank pain and hematuria.  Medical history is significant for recurrent urinary tract infections and hypothyroidism.  Blood pressure is 130/80 mm Hg and pulse is 80/min.  Physical examination shows left flank tenderness.  CT scan of the abdomen is shown below:  Urinalysis for this patient would most likely show which of the following?

Quizplus · Accepted Answer

11ec160b_3a4a_945b_9249_f917323d1406_MD0001_00 This patient's imaging shows an atrophic left kidney associated with a large, hyperdense mass filling the renal pelvis. These findings are consistent with a chronic staghorn calculus, a type of kidney stone that occurs in patients with recurrent upper urinary tract infection caused by urease-producing organisms (eg, Proteus, Klebsiella). Hydrolysis of urea yields ammonia, which alkalinizes the urine (ie, pH >7) and facilitates precipitation of struvite crystals (magnesium ammonium phosphate). Because of the large quantities of urea excreted in urine, struvite stones can grow rapidly into a branched staghorn calculus that fills the renal calyces and pelvis. Symptoms are usually related to the underlying infection (eg, fever, mild costovertebral pain, hematuria); renal colic (ie, severe flank/groin pain) is uncommon because large stones are unable to pass into the ureter and cause acute obstruction. Over time, the affected kidney can atrophy due to recurrent infection and chronic obstructive nephropathy. (Choice A) Trace or weakly positive (eg, 1 or 2+) proteinuria can be seen in a variety of disorders (eg, hematuria due to kidney stones, urinary tract infection) due to disruption of the urothelium; however, a strongly positive result (eg, 3 or 4+) is more specific for glomerular protein loss (eg, amyloidosis, diabetic nephropathy) and is not usually due to stones. (Choice B) Eosinophiluria is typically associated with acute interstitial nephritis, which is most commonly triggered by exposure to certain medications (eg, beta-lactam antibiotics, nonsteroidal anti-inflammatory drugs). Patients typically have a rash, fever, and acute kidney injury, but this condition is not associated with staghorn calculi. (Choice D) Red cell casts and dysmorphic red blood cells form when erythrocytes traverse the renal tubules and indicate a glomerular bleeding source (eg, glomerulonephritis). Staghorn calculi can cause hematuria with morphologically normal red cells due to irritation of the urothelium, but do not cause glomerular bleeding. (Choice E) Urine specific gravity correlates with urine concentration and is influenced by hydration status and regulatory hormone (eg, antidiuretic hormone) levels. Kidney stones most commonly form in concentrated urine (eg, >1.015), which results in supersaturation of salts and crystal precipitation. A specific gravity of ≤1.003 indicates dilute urine, and it is unlikely that a patient with an acute stone would have such a low specific gravity. (Choice F) Uric acid stones can occasionally form staghorn calculi but would typically be seen in patients with gout or conditions with rapid cell turnover (eg, myeloproliferative disorders) rather than recurrent urinary tract infection. This patient is much more likely to have a struvite stone. Educational objective: Struvite stones are typically seen in patients with recurrent upper urinary infection by urease-producing organisms (eg, Proteus, Klebsiella). Hydrolysis of urea yields ammonia, which alkalinizes the urine and facilitates precipitation of magnesium ammonium phosphate. Urinalysis shows hematuria and elevated urine pH. __________ References: Renal struvite stones-pathogenesis, microbiology, and management strategies. (http://www.ncbi.nlm.nih.gov/pubmed/24818849)

A 60-Year-Old Woman Comes to the Emergency Department Due to Left