Lab 4 Renal Calculi

What are kidney stones? Renal calculi (kidney stones) are formed in renal tubules, ureter or bladder. They are composed of metabolic products present in glomerular filtrate. These products are in high conc. near or above maximum solubility.

How it is formed ? Conditions leads to kidney stones High conc. of metabolic products in glomerular filtrate is due to: Low urinary volume (with normal renal function) due to restricted fluid intake Increased fluid loss from the body Increased excretion of metabolic products forming stones High plasma volume (high filtrate level) Low tubular reabsorption from filtrate

2. Changes in urine pH due to: Bacterial infection Precipitation of salts at different pH 3. Urinary stagnation is due to: Obstruction of urinary flow 4. Deficiency of stone-forming inhibitors: Citrate, pyrophosphate, glycoproteins inhibit growth of calcium phosphate and calcium oxalate crystals In type I renal tubular acidosis, hypocitraturia leads to renal stones

Kidney stones

Calcium oxalate crystal Types of kidney stones 1. Calcium salt stones 80% of kidney stones contain calcium The type of salt depends on Urine pH Availability of oxalate General appearance: White, hard, radio-opaque Calcium PO4: stag-horn in renal pelvis (large) Calcium oxalate: present in ureter (small) Calcium oxalate crystal

Causes of calcium salt stones: 1. Hypercalciuria: Increased urinary calcium excretion Men: > 7.5 mmols/day Women > 6.2 mmols/day May or may not be due to hypercalcemia 2. Hyperoxaluria: Causes the formation of calcium oxalates without hypercalciuria Diet rich in oxalates Increased oxalate absorption in fat malabsorption 3. Primary hyperoxaluria: Due to inborn errors Urinary oxalate excretion: > 400 mmols/day

Treatment: Treatment of primary causes such as infection, hypercalcemia, hyperoxaluria Oxalate-restricted diet Increased fluid intake Acidification of urine (by dietary changes) Note: Most of Calcium salt stones are formed in alkaline urine

2. Uric acid stones General appearance: About 8% of renal stones contain uric acid May be associated with hyperuricemia (with or without gout) Form in acidic urine General appearance: Small, friable, yellowish May form stag horn Radiolucent (plain x-rays cannot detect) Visualized by ultrasound or i.v. pyelogram Uric acid crystal

Treatment: The last 2 choices Purine-restricted diet Alkalinization of urine (by dietary changes) Increased fluid intake The last 2 choices

3. Mg ammonium PO4 stones About 10% of all renal stones contain Mg amm. PO4 Also called struvite kidney stones Associated with chronic UTI From Microorganisms (such as Proteus genus) that metabolize urea into ammonia Causing urine pH to become alkaline and stone formation Commonly associated with staghorn calculi 75% of staghorn stones are of struvite type

Treatment: Treatment of infection Urine acidification Increased fluid intake

4. Cystine stones Treatment: A rare type of kidney stone Due to homozygous cystinuria Form in acidic urine Soluble in alkaline urine Faint radio-opaque Treatment: Increased fluid intake Alkalinization of urine (by dietary changes) Penicillamine (binds to cysteine to form a compound more soluble than cystine)

Laboratory investigations If stone has formed and removed: Chemical analysis of stone helps to: Identify the cause Advise patient on prevention and future recurrence If stone has not formed: This type of investigation identifies causes that may contribute to stone formation

Tests are performed for this purpose: 1. Blood chemistry 2. Serum Calcium, Phosphate. Uric acid. Alkaline phosphates. sodium potassium chloride. Magnesium. Creatinine. 3. Urinalysis Volume, calcium, oxalates and cystine levels Urine pH > 8 suggests urinary tract infection (Mg amm. PO4)

Microscopy of urine Urine examination is recommended on a freshly voided morning sample using dip stick test and microscopic examination and culture. Microscopy may reveal the following crystals: oxalate (envelope) calcium phosphate (amorphous) triple phosphate (coffin lid) uric acid (needle shaped) and cystine (hexagonal) as well as any other formed elements.

Stone analysis X-ray/imaging techniques The content of the stone may determine the subsequent evaluation of the patient by this method. The presence of uric acid, cystine or struvite will have therapeutic consequences. Chemical qualitative analysis is generally adequate. X-ray/imaging techniques If a calculus is suspected, intravenous pyelography (urogram) should be included. It may also reveal structural abnormalities

X-ray/imaging techniques Renal Calculi

Chemical Examination Wash the calculi well with tap water followed by distilled water Dry well by oven Grand the calculi to obtain a smooth powder Take a small part of the powder and burn on direct flame to determine if the stone contain organic components or not.

Test for uric acid 1-Powder+ Uric acid indicator(U.A). 2-Incubation for 5 min. in RM. 3-Color pink will be appear if the U.A form it.

Test for oxalate, calcium, magnesium and phosphate Powder + 6% HNO3+heat to boil then leave it to cooled ppt .then filtrated it. The filtrate make the following on it: Filtrate + (2.5 %)CaCL2 +ammonia: If white ppt appeared. so there is oxalate Filtrate + Reagent(phosphor) ammonium molibdate : Blue Color will be appear if the there is phosphor. Filtrate + HCL: after a good mixing filter it and add H2SO4 to the precipetate on the filter paper to dissolve it, and heat then add KMO4 drop by drop if the permanganate color disappeared the calculi contains Calcium if there is no change in color the calculi is Mg.