Kidney stones

Question 1

Kidney stones is referred to as ???. It is the presence of ??? Stones (calculi) within the urinary system.

Answer 1

Nephrolithiasis. Crystalline stones.

Question 2

Renal stones are Mineral depositions that form from microscopic crystals in the loop of henle, distal tubules or the collecting duct. They basically form as a result of too much solute and not enough solvent (filtrate/urine). In other words, they form when the urine contains more solutes than the fluid in your urine can dilute

Question 3

Risk factors for kdiney stones

Answer 3

50% have genetic componen.

Positive family history has RR of 2.5

BMI greater than 27 increases RR by 2/immobile or sedentary/UTI/dehydration

Vegetarian reduces RR by 0.5

High fruit reduces RR by 0.6

High fibre reduces RR by 0.5

Obesity

Question 4

There are different ways of naming renal stones based on their composition, but also by their location.

Nephrolithiasis - stone in the ?

Ureterolithiasis - stone in the ?

Cystolithiasis - stone in the ?

Also by composition. The types of stones are>

Answer 4

Nephrolithiasis - stone in the kidney

Ureterolithiasis - stone in the ureter

Cystolithiasis - stone in the bladder

Calcium oxalate/Calcium phosphate

Struvite

Urate

Cysteine

Mixed

Question 5

What are the prevelance of kidney stones by composition?

Answer 5

Calcium oxalate and calcium phosphate make up about 80% - 40% each

Magnesium Ammonium phosphate - also called struvite - 5-10%

Urate/Uric acid; 5-10%

Cystine - 1-2%

Mixed stones

Question 6

There are 3 steps to evaluating a possible kidney stone.

History - Renal colic, passage of stones in urine, blood in urine, infection, family history, diet

Examination - flank tenderness, signs of infection on urinalysis, obesity, hypertension, gouty tophi, diabetes

Investigation - imaging, serum and urine biochemistry

RECITE

Question 7

The main imaging you would use in first instance would be ??. For a definitive diagnosis, you would then likely use ???

Answer 7

Ultrasound first, then CT- although CT is actually more sensitive. If you wanted to be absolutely definitive then probably answer CT In exam.

Question 8

Another disease that can affect the kidneys as a result of excess calcium is nephrocalcinosis. When there is lots of excess calcium in the bloodstream, and then deposits in kidney. Another disease is a congenital condition, whereby there is cystic dilation of the collecting tubules, predisposing to stone formation. This is known as ???

Answer 8

Medullary Spongey Kidney

Question 9

You can also determine the type of stone (somewhat) by CT. Low density stones (and thus show darker on CT), are ?? And ??. High density stones are>??

Answer 9

Low density - Cysteine and Struvite

High density - Calcium

Question 10

In investigation for kidney stones, urine and serum biochemistry is done in order to detect the underlying cause of kidney stones. Unsurprisingly conditions that give you high calcium give you stones. Name some of these

Answer 10

Primary hyperparathyroidism

Hypercalcemia

Idiopathoic Hypercalciuria

Question 11

Name potential underlying causes of the High oxalate, high Urate or high cysteine

Answer 11

• Primary/secondary hyperoxaluria
• Hyperuricaemia
• Cystinuria (autosomal recessive disease that leads to excess cysteine formation in urine)

Question 12

The environment of the filtrate in the tubules can also cause stones. What substance is protective against kidney stones?

Answer 12

Citrate - low citrate increases risk of stones

Renal tubular acidosis can also increase risk of stone formation.

Question 13

What serum biochemistry tests would you do to determine the cause of kidney stones?

Answer 13

• Calcium
• phosphate
• PTH
• Urate
• bicarbonate

Question 14

What biochemistry urine tests would you do for suspected kidney stones>

Answer 14

• Look at urine volume
• urinary pH
• Calcium
• sodium
• oxalate
• citrate
• creatinine
• Uric acid
• cysteine

Question 15

Why is it important to look at Urine PH when determining cause of kidney stones?

Answer 15

• Calcium stones precipitate at pH greater than 7
• Struvite stones precipitate at pH also greater than 7
• Uric acid and cystine stones precipitate at pH <6

Question 16

You can also do microscopy to look at urine under microscopy - different crystals have different shapes - basically never done though

Question 17

Stone treatment depends on where it is in the urinary Tract.

If the stone was in the kidney:

• For stone less than 2cm, you can offer symptomatic treatment until it passes, or offer ????? - ESWL - basically guided by ultrasound, you use a machine that sends high energy waves which break the stones into ?????
• For stones that are greater than 2cm, then once again you can also wait until they pass, or ??????? - pul.
• Large banched stones may require both ESWL and PUL.
• Some stones that are particulary large may require open surgery to remove them. - called a neprholithotomoy

Answer 17

• For stone less than 2cm, you can offer symptomatic treatment until it passes, or offer extracorporeal shock wave lithotripsy - ESWL - basically guided by ultrasound, you use a machine that sends high energy waves which break the stones into smaller pieces
• For stones that are greater than 2cm, then once again you can also wait until they pass, or percutaneous ultrasonic lithotripsy - pul.
• Large banched stones may require both ESWL and PUL.
• Some stones that are particulary large may require open surgery to remove them.

Question 18

Stones in the uterur treatment depends on the size and location in the uterur.

Question 19

If the uterus are continually being blocked with stones; ureteric stents can be used: they drain the kidney, thereby alleviating ??. They dialate the ureter and allow any ?? To pass. They also make it easier to perform procedures like ESWL and uteroscopic procedures.

Question 20

So lets say the stone has been dealt with. You dont really need any follow up if its your first stone, or if they are very infrequent (i.e every 10 years). If not, what follow up would you suggest?

Answer 20

periodic imaging to check stone levels

Ensure adequeyte fluids and possible consider citrate

Stone specific advice

Question 21

What are the secondary prevention strategies for calcium stones>

Answer 21

Question 22

Secondary prevention of Uric acid stones and cystine stones

Question 23

Magnesium ammonium phosphate stones (struvite) are particularly large, and may require debulking surgery. These stones are actually formed as a result of ????. As such to prevent further stones, you have to treat the infection. Many bacteria produce ???, which leads to the production of ammonium

Answer 23

Magnesium ammonium phosphate stones (struvite) are particularly large, and may require debulking surgery. These stones are actually formed as a result of UTIs. As such to prevent further stones, you have to treat the infection. Many bacteria produce urease, which leads to the production of ammonium, so it makes sense that they can contribute to formation of struvite stones.

Question 24

Citrate is an important inhibitor of stone formation. What are it’s mechanisms of action for different compositions of stone?

Answer 24

• Binds calcium, forming complexes - thereby inhibits calcium aggregation and crystal growt
• increases the activity of Tamm-Horsfall protein, which inhibits calcium and oxalate aggregation
• Alkanising effect on the turbine, which inhibits Urate and cystine stones.

Levels of citrate can be increased by low sodium dietst