RENAL

Question 1

Ureteric Calculi Risk Factors

Answer 1

Risk factors

•most calculi have no identifiable cause

Idiopathic hypercalciuria

• genetic disposition
• more common in people of Mediterranean / Middle Eastern origin

Recurrent UTIs

• especially for staghorn calculi
• UTI present in about 8% of cases
• more common in females and those with symptoms
• however many patients with low grade infection are asymptomatic

Hyperuricaemia

• primary
• following chemotherapy

Hypercalcaemia

Congenital malformations

• bifid ureters
• ureterocoeles
• medullary sponge kidney
• horseshoe kidney
• PCK
• pelvic kidney

Drugs

• carbonic anhydrase inhibitors
• topirimate
• ephedrine
• guaifenesin
• calcium and Vit D
• triamterene
• indinavir and other retrovirals
• sulfadiazine

Other

• inflammatory bowel disease - hyperoxaluria
• RTA
• renal tuberculosis

Question 2

Types of Renal Stones

Answer 2

Types of calculi

Calcium - PO4 / oxalate

• 70% of calculi
• nearly always radio-opaque
• usually no clear identifiable cause or idiopathic hypercalciuria (10 - 15%)
• prevention
• increase urine output to 2-3 litres /day
• thiazides decrease urinary calcium concentration
• restrict animal protein intake to < 350 g/day
• restrict dietary sodium and oxalate intake

Infection stones

• MgNH4PO4 stones
• also known as struvite stones
• 15% of stones
• more common in women
• ammonium generated by high urinary pH caused by urea splitting organisms
• Proteus
• Klebsiella
• Pseudomonas
• Enterococci
• can grow rapidly in size, especially during pregnancy
• treatment
• lithotripsy
• renacidin infusion

Renacidin

• contains several multi-valent organic acids and Mg2+ buffered to a pH of 3.7
• causes Mg2+ exchange with the Ca2+ in the stone
• removes the small crystal deposits from the mucosa of the renal pelvis that lithotripsy cannot

Urate

• calculi are usually radiolucent
• 5-10% of all stones
• urine pH is always below 6
• approximately 50% of stones can be dissolved using 20mEq potassium citrate orally tds for 3 months
• patients may report the passage of gravel on urination when the stone passes
• prevention
• allopurinol
• increased urine output

Cysteine

• most likely stone type to cause end stage renal failure
• cystine is the more soluble, oxidised dimer easily reducible back to cysteine within cells

Cystinuria

• consider in patients with first episode of renal colic under the age of 30
• autosomal recessive inheritance
• defective tubular reabsorption of
• cysteine
• ornithine
• arginine
• lysine

•stone formation likely if urinary cysteine > 1.2 mmol/L

-24 hour urine collection more accurate 3 months after acute episode

Calculi

• may grow rapidly
• can cause staghorn calculi
• very commonly recurrent
• CT features
• ground glass appearance
• may contain low attenuation voids

Prevention

• very high urine output (5 - 6 L/day)
• penicillamine

-forms soluble complex with cystine

•urinary alkalinisation pH > 7.5

Management

• poor fragmentation with lithotripsy
• staghorn calculi can be dissolved by percutaneous bicarbonate infusions over a few days

Drug related calculi

• usually small
• usually radiolucent
• may even be missed by CT

Question 3

Renal Colic Criteria for admission

Answer 3

Criteria for admission

•present in approximately 10% of cases

Short stay ward

• ongoing pain 4 hours following adequate IV and NSAID analgesia
• stone
• < 6 mm diameter
• in distal ureter

Urological admission

•any obstruction of a solitary kidney

-renal transplants fall into this category

• urinary infection
• high degree of obstruction
• large (> 6mm) proximal stone
• bilateral ureteric stones
• significant renal impairment and associated urinary obstruction
• persistent or multiple repetitive episodes of pain requiring parenteral analgesia