Past Patient History Diagnosed with cystinuria as a child Left side nephrectomy as a child secondary to damage by cystine stones Recurrent kidney stones in the remaining right kidney Nephrostomy tube placed into remaining kidney
Questions to be Considered: 1.) How does the patient’s current renal problems relate to the cystine crystals found? 2.) What laboratory tests are performed to confirm the presence of cystine crystals in the urine? 3.) What are the long term effects of cystine crystal formation? 4.) Are there treatments available for patients with cystinuria?
Pathogenesis of Cystinuria Autosomal recessive disorder Involves a defect in the renal transport of cystine by the tubules Defect results in lack of cystine reabsorbtion of the kidney Homozygous patients usually the only ones to present with problems Heterozygotes have a milder form of cystinuria (cystine crystals found in urine during analysis but don’t usually form stones)
Solubility within the Kidney Normal excretion of amino acids such as cystine into the urine is about 100 mg/day Heterozygous excrete around mg/day Homozygous excrete around mg/day Solubility limit is around mg/day Stones composed of cystine form when the concentration of cystine exceeds the normal solubility levels and the excess cannot go into solution (cystine crystals favor the existing free cystine and will compound it to form the stone)
Cystine Confirmation Initially found during a microscopic urinalysis –crystals are found in neutral to acidic pH and are flat hexagonal shapes Confirmation test for cystine once crystals are found microscopically is a cyanide-nitroprusside test –involves mixing the urine with sodium cyanide and then sodium nitroprusside which will chemically react to produce a red-purple color indicative of presence of cystine crystals in the urine
Positive Nitroprusside Reaction: Left side: Negative control Right side: Positive for cystine
Long Term Effects of Cystinuria Recurrent stone formation as seen with this patient Possible nephrectomy due to renal failure Pain associated with stone formation and passage
Treatments Focus is on management Relief of symptoms (pain medications) Prevention of further stones (drinking large amounts of water to dilute the urine)
Treatments - continued….. Watching diet ( avoiding methionine rich foods) Alkanization of the urine (use of sodium bicarbonate or sodium citrate to more readily dissolve the cystine) Lithotripsy (non-invasive, shock waves to break up the stone to where it can be passed) Invasive procedures for stone removal
Summary 57 year old women with presence of cystine crystals in the urine Confirmatory nitroprusside test was positive for cystine History revealed many renal problems associated with cystinuria Treatments are unpredictable
Credits This case study was prepared by Amy Albright, MT(ASCP) while she was a Medical Technology student in the 2004 MT Class at William Beaumont Hospital, Royal Oak, MI.