Cystinuria - Revision history

Danbot: Moved intro to Background bullets; removed excessive bold; added Renal tubular disorders DDX template

2026-03-19T12:09:06Z

Moved intro to Background bullets; removed excessive bold; added Renal tubular disorders DDX template

← Older revision		Revision as of 12:09, 19 March 2026
Line 1:		Line 1:
	Cystinuria is an autosomal recessive disorder of renal tubular amino acid transport causing excessive urinary excretion of '''cystine''', which precipitates into '''recurrent kidney stones'''.<ref name="StatPearls">Cystinuria. ''StatPearls''. NCBI. 2023.</ref> It accounts for ~1-2% of adult and '''6-8% of pediatric''' kidney stones. Patients present with '''renal colic indistinguishable from other stone types''' but tend to form '''larger stones, more frequently, starting at a younger age'''. The key EM considerations are recognizing the diagnosis (young/recurrent stone former), knowing that '''cystine stones are resistant to ESWL''', and ensuring '''aggressive IV hydration''' and appropriate urologic follow-up.

	==Background==		==Background==
			*Cystinuria is an autosomal recessive disorder of renal tubular amino acid transport causing excessive urinary excretion of cystine, which precipitates into recurrent kidney stones.<ref name="StatPearls">Cystinuria. ''StatPearls''.
			*NCBI. 2023.</ref> It accounts for ~1-2% of adult and 6-8% of pediatric kidney stones.
			*Patients present with renal colic indistinguishable from other stone types but tend to form larger stones, more frequently, starting at a younger age.
			*The key EM considerations are recognizing the diagnosis (young/recurrent stone former), knowing that cystine stones are resistant to ESWL, and ensuring aggressive IV hydration and appropriate urologic follow-up.
	*80% form their first stone before age 20<ref name="StatPearls"/>		*80% form their first stone before age 20<ref name="StatPearls"/>
	*Cystine stones are ~~'''~~faintly radiopaque~~'''~~ on plain film (often missed on KUB) but ~~'''~~visible on CT~~'''~~		*Cystine stones are faintly radiopaque on plain film (often missed on KUB) but visible on CT
	*Pathognomonic finding: ~~'''~~hexagonal crystals~~'''~~ on urine microscopy		*Pathognomonic finding: hexagonal crystals on urine microscopy
	*Up to 40% form mixed stones (cystine + calcium oxalate/phosphate)		*Up to 40% form mixed stones (cystine + calcium oxalate/phosphate)
	*~~'''NOT~~ [[Cystinosis]]~~'''~~ — cystinuria causes stones only; cystinosis is a lysosomal storage disease causing systemic cystine accumulation, [[Fanconi syndrome]], and multiorgan disease		*[[Cystinosis]] — cystinuria causes stones only; cystinosis is a lysosomal storage disease causing systemic cystine accumulation, [[Fanconi syndrome]], and multiorgan disease

	==Clinical Features==		==Clinical Features==
	*Presents identically to other [[Nephrolithiasis\|renal colic]]: acute flank pain radiating to groin, hematuria, nausea/vomiting		*Presents identically to other [[Nephrolithiasis\|renal colic]]: acute flank pain radiating to groin, hematuria, nausea/vomiting
	*~~'''~~Suspect cystinuria when:~~'''~~		*Suspect cystinuria when:
	**~~'''~~Young patient~~'''~~ (child, adolescent, young adult) with kidney stones		**Young patient (child, adolescent, young adult) with kidney stones
	**~~'''~~Recurrent~~'''~~ stone former with multiple procedures		**Recurrent stone former with multiple procedures
	**~~'''~~Bilateral~~'''~~ or ~~'''~~staghorn~~'''~~ calculi in a young person		**Bilateral or staghorn calculi in a young person
	**~~'''~~Family history~~'''~~ of early-onset stones		**Family history of early-onset stones
	*Complications: ureteral obstruction, infected stone, ~~'''~~chronic kidney disease~~'''~~ (higher CKD rate than typical stone formers)		*Complications: ureteral obstruction, infected stone, chronic kidney disease (higher CKD rate than typical stone formers)

	==Differential Diagnosis==		==Differential Diagnosis==
Line 21:		Line 23:
	**Calcium oxalate/phosphate (most common), uric acid (radiolucent; dissolves with alkalinization), struvite (infection stones)		**Calcium oxalate/phosphate (most common), uric acid (radiolucent; dissolves with alkalinization), struvite (infection stones)
	*Other causes of recurrent pediatric stones: primary hyperoxaluria, distal RTA, hyperparathyroidism		*Other causes of recurrent pediatric stones: primary hyperoxaluria, distal RTA, hyperparathyroidism
	*~~'''~~[[Cystinosis]]~~'''~~ — completely different disease despite similar name		*[[Cystinosis]] — completely different disease despite similar name

			{{Renal tubular disorders DDX}}

	==Evaluation==		==Evaluation==
	===Workup===		===Workup===
	*~~'''~~CT abdomen/pelvis without contrast:~~'''~~ identifies stone; cystine density typically 600-1200 HU (lower than calcium stones)		*CT abdomen/pelvis without contrast: identifies stone; cystine density typically 600-1200 HU (lower than calcium stones)
	*~~'''~~Urinalysis:~~'''~~ hematuria; look for ~~'''~~hexagonal crystals~~'''~~ (pathognomonic but not always present)		*Urinalysis: hematuria; look for hexagonal crystals (pathognomonic but not always present)
	*~~'''~~BMP:~~'''~~ creatinine, electrolytes		*BMP: creatinine, electrolytes
	*~~'''~~Urine culture~~'''~~ if fever or pyuria		*Urine culture if fever or pyuria
	*KUB is unreliable (cystine stones are faintly radiopaque and easily missed)		*KUB is unreliable (cystine stones are faintly radiopaque and easily missed)

	===Diagnosis===		===Diagnosis===
	*~~'''~~Stone analysis~~'''~~ after passage or retrieval is the most reliable confirmation		*Stone analysis after passage or retrieval is the most reliable confirmation
	*~~'''~~Hexagonal crystals~~'''~~ on urine microscopy — pathognomonic		*Hexagonal crystals on urine microscopy — pathognomonic
	*~~'''~~Cyanide-nitroprusside test:~~'''~~ positive (turns purple) when urine cystine >75 mg/L		*Cyanide-nitroprusside test: positive (turns purple) when urine cystine >75 mg/L
	*24-hour urine cystine (>300 mg/day confirms; normal <30 mg/day) — not an ED test		*24-hour urine cystine (>300 mg/day confirms; normal <30 mg/day) — not an ED test

	==Management==		==Management==
	*~~'''~~Acute episode:~~'''~~ manage per standard [[Nephrolithiasis\|renal colic]] protocols		*Acute episode: manage per standard [[Nephrolithiasis\|renal colic]] protocols
	**Aggressive ~~'''~~IV hydration~~'''~~ (both therapeutic and helps dilute cystine)		**Aggressive IV hydration (both therapeutic and helps dilute cystine)
	**~~'''~~Analgesia:~~'''~~ ketorolac, opioids as needed		**Analgesia: ketorolac, opioids as needed
	**~~'''~~Antiemetics:~~'''~~ ondansetron		**Antiemetics: ondansetron
	**~~'''~~Tamsulosin~~'''~~ for medical expulsive therapy if stone <10 mm		**Tamsulosin for medical expulsive therapy if stone <10 mm
	*~~'''~~Obstructing stone + infection:~~'''~~ '''urology emergency''' — urgent decompression (stent or nephrostomy) + IV antibiotics		*Obstructing stone + infection: '''urology emergency''' — urgent decompression (stent or nephrostomy) + IV antibiotics
	*~~'''~~Continue home medications:~~'''~~ potassium citrate, tiopronin if already prescribed		*Continue home medications: potassium citrate, tiopronin if already prescribed
	*~~'''~~Cystine stones are resistant to ESWL~~'''~~ — ureteroscopy with laser lithotripsy or percutaneous nephrolithotomy is preferred for stones requiring surgical intervention<ref name="StatPearls"/>		*Cystine stones are resistant to ESWL — ureteroscopy with laser lithotripsy or percutaneous nephrolithotomy is preferred for stones requiring surgical intervention<ref name="StatPearls"/>

	==Disposition==		==Disposition==
	*~~'''~~Admit:~~'''~~ obstructing stone with infection/sepsis, intractable pain/vomiting, AKI, solitary kidney with obstruction		*Admit: obstructing stone with infection/sepsis, intractable pain/vomiting, AKI, solitary kidney with obstruction
	*~~'''~~Discharge:~~'''~~ small (<10 mm) non-obstructing stone, controlled pain, tolerating PO, normal renal function, no infection		*Discharge: small (<10 mm) non-obstructing stone, controlled pain, tolerating PO, normal renal function, no infection
	**Urology follow-up within 1-2 weeks		**Urology follow-up within 1-2 weeks
	**'''Strain urine and send any passed stone for analysis'''		**'''Strain urine and send any passed stone for analysis'''
	**If cystinuria newly suspected (young/recurrent), arrange '''nephrology or urology referral''' for 24-hour urine and long-term prevention planning		**If cystinuria newly suspected (young/recurrent), arrange '''nephrology or urology referral''' for 24-hour urine and long-term prevention planning
	*~~'''~~Key patient instruction:~~'''~~ drink enough to produce >3 L urine daily, including a large glass at bedtime and overnight — the single most important preventive measure		*Key patient instruction: drink enough to produce >3 L urine daily, including a large glass at bedtime and overnight — the single most important preventive measure

	==See Also==		==See Also==

Ostermayer: Created page with "Cystinuria is an autosomal recessive disorder of renal tubular amino acid transport causing excessive urinary excretion of '''cystine''', which precipitates into '''recurrent kidney stones'''.Cystinuria. ''StatPearls''. NCBI. 2023. It accounts for ~1-2% of adult and '''6-8% of pediatric''' kidney stones. Patients present with '''renal colic indistinguishable from other stone types''' but tend to form '''larger stones, more frequently, startin..."

2026-03-18T02:36:14Z

Created page with "Cystinuria is an autosomal recessive disorder of renal tubular amino acid transport causing excessive urinary excretion of '''cystine''', which precipitates into '''recurrent kidney stones'''.<ref name="StatPearls">Cystinuria. ''StatPearls''. NCBI. 2023.</ref> It accounts for ~1-2% of adult and '''6-8% of pediatric''' kidney stones. Patients present with '''renal colic indistinguishable from other stone types''' but tend to form '''larger stones, more frequently, startin..."

New page

Cystinuria is an autosomal recessive disorder of renal tubular amino acid transport causing excessive urinary excretion of '''cystine''', which precipitates into '''recurrent kidney stones'''.<ref name="StatPearls">Cystinuria. ''StatPearls''. NCBI. 2023.</ref> It accounts for ~1-2% of adult and '''6-8% of pediatric''' kidney stones. Patients present with '''renal colic indistinguishable from other stone types''' but tend to form '''larger stones, more frequently, starting at a younger age'''. The key EM considerations are recognizing the diagnosis (young/recurrent stone former), knowing that '''cystine stones are resistant to ESWL''', and ensuring '''aggressive IV hydration''' and appropriate urologic follow-up.

==Background==
*80% form their first stone before age 20<ref name="StatPearls"/>
*Cystine stones are '''faintly radiopaque''' on plain film (often missed on KUB) but '''visible on CT'''
*Pathognomonic finding: '''hexagonal crystals''' on urine microscopy
*Up to 40% form mixed stones (cystine + calcium oxalate/phosphate)
*'''NOT [[Cystinosis]]''' — cystinuria causes stones only; cystinosis is a lysosomal storage disease causing systemic cystine accumulation, [[Fanconi syndrome]], and multiorgan disease

==Clinical Features==
*Presents identically to other [[Nephrolithiasis|renal colic]]: acute flank pain radiating to groin, hematuria, nausea/vomiting
*'''Suspect cystinuria when:'''
**'''Young patient''' (child, adolescent, young adult) with kidney stones
**'''Recurrent''' stone former with multiple procedures
**'''Bilateral''' or '''staghorn''' calculi in a young person
**'''Family history''' of early-onset stones
*Complications: ureteral obstruction, infected stone, '''chronic kidney disease''' (higher CKD rate than typical stone formers)

==Differential Diagnosis==
*Other causes of [[Nephrolithiasis|renal colic]] (stone type cannot be determined clinically):
**Calcium oxalate/phosphate (most common), uric acid (radiolucent; dissolves with alkalinization), struvite (infection stones)
*Other causes of recurrent pediatric stones: primary hyperoxaluria, distal RTA, hyperparathyroidism
*'''[[Cystinosis]]''' — completely different disease despite similar name

==Evaluation==
===Workup===
*'''CT abdomen/pelvis without contrast:''' identifies stone; cystine density typically 600-1200 HU (lower than calcium stones)
*'''Urinalysis:''' hematuria; look for '''hexagonal crystals''' (pathognomonic but not always present)
*'''BMP:''' creatinine, electrolytes
*'''Urine culture''' if fever or pyuria
*KUB is unreliable (cystine stones are faintly radiopaque and easily missed)

===Diagnosis===
*'''Stone analysis''' after passage or retrieval is the most reliable confirmation
*'''Hexagonal crystals''' on urine microscopy — pathognomonic
*'''Cyanide-nitroprusside test:''' positive (turns purple) when urine cystine >75 mg/L
*24-hour urine cystine (>300 mg/day confirms; normal <30 mg/day) — not an ED test

==Management==
*'''Acute episode:''' manage per standard [[Nephrolithiasis|renal colic]] protocols
**Aggressive '''IV hydration''' (both therapeutic and helps dilute cystine)
**'''Analgesia:''' ketorolac, opioids as needed
**'''Antiemetics:''' ondansetron
**'''Tamsulosin''' for medical expulsive therapy if stone <10 mm
*'''Obstructing stone + infection:''' '''urology emergency''' — urgent decompression (stent or nephrostomy) + IV antibiotics
*'''Continue home medications:''' potassium citrate, tiopronin if already prescribed
*'''Cystine stones are resistant to ESWL''' — ureteroscopy with laser lithotripsy or percutaneous nephrolithotomy is preferred for stones requiring surgical intervention<ref name="StatPearls"/>

==Disposition==
*'''Admit:''' obstructing stone with infection/sepsis, intractable pain/vomiting, AKI, solitary kidney with obstruction
*'''Discharge:''' small (<10 mm) non-obstructing stone, controlled pain, tolerating PO, normal renal function, no infection
**Urology follow-up within 1-2 weeks
**'''Strain urine and send any passed stone for analysis'''
**If cystinuria newly suspected (young/recurrent), arrange '''nephrology or urology referral''' for 24-hour urine and long-term prevention planning
*'''Key patient instruction:''' drink enough to produce >3 L urine daily, including a large glass at bedtime and overnight — the single most important preventive measure

==See Also==
*[[Nephrolithiasis]]
*[[Cystinosis]]
*[[Fanconi syndrome]]
*[[Renal colic]]

==External Links==
*[https://www.ncbi.nlm.nih.gov/books/NBK470527/ StatPearls — Cystinuria]
*[https://pmc.ncbi.nlm.nih.gov/articles/PMC9317473/ Urol Ann — Cystinuria: Overview of Diagnosis and Medical Management (2022)]
*[https://www.ncbi.nlm.nih.gov/books/NBK619248/ GeneReviews — Cystinuria]

==References==
<references/>

[[Category:Renal]]
[[Category:Pediatrics]]