What are Kidney Stones?

Susannah Hollywood - 2000 word in-depth article - created July 2023

What are Kidney Stones?

Overview

Kidney stones are solid masses created by crystallisation and clumping together of chemicals in urine. Formed in the kidney, these stones may move into the rest of the urinary system through the ureters (tubes connecting kidneys and bladder), bladder and urethra (tube leading from the bladder through which urine leaves the body).

Kidney stones can range in size, and smaller ones may pass through the urinary system and be excreted from the body in urine without symptoms. However, larger ones can cause severe pain and urinary blockage, and may result in infection and damage to the urinary system.

Stones are usually irregular in shape and can have smooth or jagged surfaces. According to the US National Institute of Diabetes and Digestive and Kidney Disease (NIDDK), kidney stones can range from the size of a grain of sand to the size of a pea. In rare cases, they can reach the size of a golf ball. You can have just one kidney stone, or several.

As the most common disorder of the urinary system,1 kidney stones will be experienced by 8.8% of people (in the US) during their lifetime.2 You are at greater risk of having a kidney stone if you have had one previously or have a family history of them.

Urine is a liquid waste product, produced by filtration of the blood by the kidneys. Urine is made of surplus water containing many different dissolved chemicals, including urea, salts and creatinine. This fluid passes from the kidney through the urinary system and is excreted from the body via urination. This process helps to maintain the optimal balance of chemicals and water in blood, and to keep it clean.

Under certain conditions, the dissolved chemicals present in urine can crystallise. Small crystals can join together and attract other organic matter, resulting in the formation of larger solid deposits, known as kidney stones.

Kidney stones are known by several other names, including renal stones, renal calculi,3 nephrolith, nephrolithiasis and urolithiasis.4

Types of kidney stones

Kidney stones can be formed from different chemicals. The most common ones are:1

Calcium stones – make up 80% of all stones.4 Formed of calcium oxalate (most commonly) or calcium phosphate or a combination of both.

Struvite stones – usually caused by urinary tract infection.

Uric acid stones – formed in acidic urine which can be caused by diet or by other underlying health conditions. Can run in families.

Cystine stones – rarely found and caused by the inherited genetic defect, cystinuria which increases levels of the amino acid, cystine, in the urine. Can run in families.

Other – in rare cases, stones can be formed from other chemicals

Causes of kidney stones

Kidney stones are formed by the crystallisation of chemicals in urine. According to The British Association of Urological Surgeons, this process results from:

● High concentration of certain chemicals in urine

● Insufficient levels of chemicals that prevent crystallisation in urine

● Insufficient volume of urine

The formation process is complex, often multifactorial and can differ from person to person. Contributory factors include diet and lifestyle, genetics, medications and other health conditions.

Risk factors

The composition and concentration of urine, and so the likelihood of crystal formation, is influenced by many different processes in the body. These include:

Genetic risk factors:3

● People who are assigned male at birth (AMAB) are more likely to have stones than those assigned female at birth (AFAB)

● Personal history of previous stones

● Family history of kidney stones

Dietary risk factors:5

● Insufficient fluid intake

● Low calcium intake

● Low fruit and vegetable intake

● High sodium intake

● High animal protein (fish and meat) intake

● High oxalate intake (further information on high oxalate foods here)

Other health conditions:

There are a wide range of health conditions which can increase the risk of kidney stone formation. These include obesity, diabetes, hypertension 3 (high blood pressure) and metabolic syndrome.6 Conditions which affect chemical levels in blood or urine, and others which influence absorption of fluid and nutrients by the gastrointestinal system may also increase risk. In addition, conditions of the kidney and urinary system - including structural abnormalities, kidney disease and recurrent urinary tract infections - may be contributory.

More information can be found here: The US National Institute of Diabetes and Digestive and Kidney diseases

Medications:

There are a small number of medications which may increase the risk of development of kidney stones. A list of these can be found on the NHS website.

Signs and symptoms of kidney stones

Stones that stay in the kidney may not produce any symptoms. However, once a stone leaves the kidney and enters the rest of the urinary system, it must pass through narrow tubes and this can cause urinary obstruction and hydronephrosis (swelling of the kidney due to build-up of urine), spasms of the ureter or bladder muscles, and infections of the kidney or urinary tract.

The following symptoms may result:

● Pain - acute, often severe pain in the flank (the side of the low back), possibly radiating to the abdomen, groin, testicle and labia. Pain may fluctuate in intensity, coming in waves,7 and may change as the stone passes through different parts of the urinary system. Intense pain experienced in waves is called renal colic.

● Nausea, vomiting3

● Changes to urination including:

○ Pain/burning

○ Presence of blood in urine

○ Urine which is cloudy or has an unusual smell

○ Intense need to urinate and frequent urination

○ Difficulty urinating

● Fever, chills7

● Costovertebral tenderness3

Diagnosis of kidney stones

The following procedures may be used to confirm a diagnosis of kidney stones and exclude other conditions which can present with similar symptoms:

● History taking including:

○ general health and past medical history

○ family history of kidney stones

○ diet and lifestyle including intake of fluid, protein, sodium, high oxalate foods, fruits/vegetables, supplements

● Physical exam including examination of abdomen and back for signs such as:

○ costovertebral angle tenderness (the space between the bottom rib and the spinal column in the back)8

○ hypoactive bowel sounds (reduction in bowel sounds indicative of an underactive gastrointestinal system)7

● Urine tests - carried out with a urine dipstick or by laboratory analysis to check urine for:

○ pH levels

○ blood

○ infection

○ presence of crystals

○ levels of chemicals involved in stone formation

Certain tests can be carried out using an individual sample, however more detailed analysis may require urine collection over a 24 hour period.

● Blood tests to check:

○ kidney function

○ other underlying health issues

○ levels of chemicals involved in stone formation

● Imaging tests:

○ X-ray KUB - 2-dimensional imaging of the kidney, ureter and bladder using X-ray

○ CT KUB - 3-dimensional imaging of the kidney, ureter and bladder using CT scan (Computerised Tomography).

○ Intravenous pyelogram - X-ray images taken after injection of contrast dye

○ Ultrasound - Although this technique has diagnostic limitations with kidney stones, it can be useful in cases when other imaging techniques may be contraindicated, for example during pregnancy.

CT KUB is considered the most accurate way of confirming diagnosis.7 It can also provide detailed information about the stone - its size, shape, how hard or soft it is likely to be, and where it is located within the urinary tract - all useful in guiding treatment choices.

● Analysis of stone once passed - to determine chemicals involved in formation, which may indicate certain underlying processes or conditions

Management and treatment for kidney stones

Stones will often pass on their own, exiting the body in urine, particularly those that are small in size (less than 5mm).7 This process may be aided by:

● Additional fluids – possibly IV (intravenous)7

● Pain relief – often in the form of NSAIDS (non steroidal anti-inflammatories)3, 9

● Alpha blocker medications – used to relax the ureter muscles, most effective for larger stones 9, 10

● Antibiotics – to treat infections when present7

● Antiemetics 7 – to reduce nausea and vomiting

80-90% of stones will pass in this way, without more significant intervention.7 Follow up imaging may be used to track progress.9

Larger stones, or those causing infection or obstruction, may require more intervention. The treatment chosen will depend on the size, shape and location of the stone, as well as general health issues and current medication in each case.

There are a number of procedures which can be used either to remove the stone or to break it up to allow it to pass out of the body in urine. These include:

● Extracorporeal shock wave lithotripsy – a non-invasive procedure involving the use of sound waves to create vibrations which break a stone into smaller pieces, allowing it to pass out of the body in urine.

● Percutaneous nephrolithotomy and percutaneous nephrolithotripsy – surgery to remove kidney stones involving a small incision made in the back. The stone is removed either whole (Nephrolithotomy), or after being broken into smaller pieces (Nephrolithotripsy) Usually performed under general anaesthesia.

● Ureteroscopy – insertion of a small scope (a thin flexible tube with a camera at the end) into the urinary system via the urethra to find and remove a kidney stone, either whole or after breaking it up into smaller fragments.

Prevention of recurrence

Once an acute episode is resolved, patients may be treated to prevent recurrent kidney stones. The choice of preventative treatment will depend on the type of stone and what has caused it. This is determined by analysis of blood, urine and stone composition, and may include:

● Diet and lifestyle changes to optimise chemical levels in the blood, maintain optimal body weight, balance blood sugars and reduce hypertension:

○ Drinking sufficient volume of fluids daily to reduce the concentration of chemicals in urine and prevent crystal formation. 2.5 - 3 litre per day is recommended9 or sufficient to produce 2 litres of urine per day1, 3, 7

○ Maintaining recommended calcium intake, neither significantly above or below*

○ Reducing sodium intake*

○ Reducing animal product intake

○ Increasing fibre and vegetable intake

○ Reducing carbonated drinks

○ Reducing refined sugar intake

● Drug therapy to address metabolic imbalances and other underlying conditions, for example:

○ Citrate supplements 9 to reduce the acidity of urine

○ Thiazide diuretics 7 to help the body to get rid of water

○ Allopurinol 7 to reduce levels of uric acid in the blood

* Calcium stones are the most common type of kidney stone, and high concentrations of calcium in urine are a risk factor for their formation. However, this is not necessarily caused by high intake of calcium in food and drink. Instead, high calcium levels in urine may be due to high sodium intake. When the kidneys filter out excess sodium from blood, calcium is pulled across with it into the urine. Reducing sodium intake may therefore be a more effective way of reducing calcium levels in the blood than reducing calcium intake. Calcium is important for the body in many ways and intake should be kept at recommended levels.

The specific recommendations for dietary changes will depend on the individual case and a Dietician may be able to provide these. More information can be found on the National Institute of Diabetes and Digestive and Kidney Diseases website.

Complications of kidney stones

The National Kidney Foundation states that kidney stones can be a cause of chronic kidney disease and (rarely) of sepsis, a life threatening condition resulting from an infection.

FAQs

How can I prevent kidney stones?

Kidney stone formation is complex and multifactorial, with a number of potential contributory factors. However, general preventative recommendations include:

● Ensuring adequate fluid intake of 2.5-3 litres per day

● Reducing intake of salt, sugar, animal protein and oxalate-rich foods

● Maintaining optimal calcium intake, ideally through food rather than supplements

● Maintaining an optimal body weight

How common are kidney stones?

Kidney stones are a common urological condition, affecting 8.8% of the US population in their lifetime, more common in people AMAB than those AFAB (10.6% compared to 7.1%).2

The number of people experiencing kidney stones seems to be increasing overall.2, 9 You are more likely to have a kidney stone if you have had one previously or have a family history of them.

What can I expect if I have kidney stones?

Kidney stones that stay in the kidney, or small stones which pass through the urinary system easily, may not cause any symptoms. However, larger stones can cause severe pain as they pass through the system, and may result in urinary obstruction and infection.

When should I see a doctor?

Kidney stones can cause pain, commonly in the flank (the side of the low back), possibly radiating to the abdomen or groin. Pain may be severe and come and go in waves. Nausea and vomiting may also occur, as well as fever and chills. If you experience these symptoms, consult your doctor.

Summary

Kidney stones are solid masses which form in the urine through crystallisation of chemicals. They can range in size and small ones may pass out of the body unnoticed, however larger ones can cause severe pain, urinary tract obstruction and infection. There are a number of underlying processes which contribute to their formation, including diet and lifestyle factors.

References

Vancouver Style

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Ziemba JB, Matlaga BR. Epidemiology and economics of nephrolithiasis. Investig Clin Urol [Internet]. 2017 [cited 2023 Jul 9];58(5):299. Available from: https://icurology.org/DOIx.php?id=10.4111/icu.2017.58.5.299

Nojaba L, Guzman N. Nephrolithiasis. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 [cited 2023 Jul 9]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK559227/

Thakore, Palak, and Terrence H. Liang. ‘Urolithiasis’. StatPearls, StatPearls Publishing, 2023. PubMed, http://www.ncbi.nlm.nih.gov/books/NBK559101/

Ferraro PM, Bargagli M, Trinchieri A, Gambaro G. Risk of kidney stones: influence of dietary factors, dietary patterns, and vegetarian–vegan diets. Nutrients [Internet]. 2020 Mar 15 [cited 2023 Jul 7];12(3):779. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7146511/

Chang CW, Ke HL, Lee JI, Lee YC, Jhan JH, Wang HS, et al. Metabolic syndrome increases the risk of kidney stone disease: a cross-sectional and longitudinal cohort study. J Pers Med [Internet]. 2021 Nov 6 [cited 2023 Jul 7];11(11):1154. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8622125/

Leslie SW, Sajjad H, Murphy PB. Renal calculi. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 [cited 2023 Jul 9]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK442014/

Higuchi H, Harada T, Hiroshige J. Evaluation of the usefulness of costovertebral angle tenderness in patients with suspected ureteral stone. J Gen Fam Med [Internet]. 2022 Sep 12 [cited 2023 Jul 5];24(1):56–8. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9808142/

Fontenelle, Leonardo Ferreira, and Thiago Dias Sarti. ‘Kidney Stones: Treatment and Prevention’. American Family Physician, vol. 99, no. 8, Apr. 2019, pp. 490–96. www.aafp.org, https://www.aafp.org/pubs/afp/issues/2019/0415/p490.html

Hollingsworth JM, Canales BK, Rogers MAM, Sukumar S, Yan P, Kuntz GM, et al. Alpha blockers for treatment of ureteric stones: systematic review and meta-analysis. BMJ [Internet]. 2016 Dec 1 [cited 2023 Jul 9];i6112. Available from: https://www.bmj.com/lookup/doi/10.1136/bmj.i6112