What is a Kidney Stone?
A kidney stone, also known as a renal calculus (plural ~ calculi), are crystal aggregates that form within the kidney. A stone or stone(s) will pass down the ureter and enter the bladder. Due to its passage through the urinary system, kidney stones may also be called urinary stones or the term nephrolithiasis is used to refer to the presence of kidney stones.
The term ureterolithiasis refers to stones in the ureter(s) – usually stones form in the kidneys but grow further in the ureter, where they cause the most notable pain. Some stones may pass out with the urine while others will require medical intervention like surgery or ultrasound ‘shock waves’ or laser ‘blasting’.
There are a number of causes of kidney stones but in most cases the formation of the kidney stones are the same. A high concentration of certain substances within the urine will cause precipitation. With time these substances aggregate and a kidney stone is formed. It may continue growing further while it passes through the rest of the urinary system.
Size of Kidney Stones
The size of kidney stones may vary in size – calculi can be small like fine sand or large round stones may be found in the bladder. Stones that are 2 to 4 mm may pass out with much pain while stones larger than 5 to 6 mm can result in obstruction and require intervention. Frequent stones or those as large as 7mm to 8mm can result in serious complications.
The most common symptoms of kidney stones include kidney pain, pain from the flanks to the groin, pain upon urination (dysuria), nausea, vomiting, changes in urine color or blood in the urine (hematuria). Less frequently, a fever and chills may be present.
Types of Kidney Stones
Most kidney stones contain calcium but other compounds, particularly the breakdown products of proteins, may also form kidney stones. The types of crystals that give rise to kidney stones are listed below in order of prevalence.
- Calcium oxalate (sometimes calcium phosphate) stones
- Magnesium ammonium phosphate (struvite) stones
- Urate/uric acid stones
- Hydroxyapatite stones
- Brushite stones
- Cystine stones
- Mixed stones
Shape, Color of Stones
- Calcium oxalate- spiky, uneven jagged, brown.
- Calcium phosphate – smooth.
- Struvite – staghorn, tan color.
- Urate – smooth, brown.
- Cystine – yellow crystalline.
Kidney Stone Pain (Renal Colic)
Kidney stone pain, or renal colic, is the pain caused by the passage of a kidney stone through the urinary tract. As a stone forms in the kidney, it usually does not cause pain. It then passes into the ureter where it grows further and since the ureter is narrow, it causes significant inflammation as it scrapes the ureteral wall. This will result in flank pain that extends all the way down to the groin and also radiates to the lower back and groin. The shape and size of the kidney stone are other aspects to consider in renal colic – while almost every case is painful, sharp or spiky stones and large stones may be more painful.
The intensity of kidney stone pain varies but it usually described as severe or excruciating. Kidney pain may be pain in the mid back or upper part of the flanks that can be a result of many possible kidney related disorders. Kidney pain may or may not be due to kidney stones. Kidney stone pain may be accompanied by other signs and symptoms like nausea, vomiting, dizziness, bloody urine (hematuria), straining and pain/burning upon urination.
Causes of Kidney Stones
Individual susceptibility is an important factor to consider in the development of kidney stones. There a number of factors, including dietary, environmental, situational and genetic factors as well as diseases, that may precipitate the formation of kidney stones. The reason why it occurs in some people and not in others facing the same factors in unknown. However, a number of risk factors for kidney stone development is known.
Low Fluid Intake
Drinking less water or other fluids will decrease urine output. It will also concentrate urine. This will reduce the flushing out of waste products in the urine and allow solutes to precipitate. Drinking caffeinated drinks and alcohol can contribute further towards the development of kidney stones as it dehydrates the body by increasing urine output.
Seasonal episodes of kidney stones may be related to summer or heat waves as the body lose fluid through perspiration (sweating) and urine output decreases. Vitamin D production due to sunlight exposure also increases in summer and this may be a contributing factor in seasonal episodes, especially in a person who is accustomed to living in an area with limited sun exposure.
Low urine output
Urinating less frequently and low urine volumes are another predisposing factor for the development of kidney stones. Since kidney stones continue to grow further in the other structures of the urinary system, holding back urination on a ‘full bladder’ can increase the size of stones.
Foods, Supplements and Beverages
Foods rich in oxalate, like spinach and rhubarb, and high protein foods may contribute towards the development of oxalate stones and uric acid stones. There are a number of other foods to avoid for the prevention of kidney stones. Caffeinated drinks, like tea, coffee and certain soft drinks, and alcohol can dehydrate the body thereby increasing the risk of developing kidney stones. High doses of vitamin C and even moderate doses of vitamin D supplements increase the risk of kidney stones – vitamin C increases oxalate secretion while vitamin D increases calcium absorption and excretion.
Certain drugs may increase the risk of kidney stone development. These include drugs like :
- Diuretics (some diuretics may help reduce recurrent stones)
If there is a family history of kidney stones, a person may be up to three times more likely to develop stones in the course of their life. Some conditions which may be linked to genetic factors include :
While there may be a genetic susceptibility, dietary habits among family members may be similar which could further contribute to the development of kidney stones.
A person prone to repeated urinary tract infections (UTI’s) may be at risk of developing struvite stones. Bacteria in the urine may alter the pH level (acid-base balance) of urine. This can trigger the formation of struvite stones.
Intestinal, Bowel Disorders
Certain diseases of the bowels, including inflammatory bowel disease and disorders that affect the small intestine, particularly the ileum, may increase oxalate absorption and excretion. Surgical removal of the ileum (resection) may also contribute to this.
Any abnormalities of the urinary tract may affect the flow of urine, resulting in pooling or backing up of fluid. This can lead to hydronephrosis which is the accumulation of urine within the kidney. Disruptions in the flow of urine may at times be due to therapeutic measures like a catheter or stent. Some of these abnormalities may be congenital (present at birth) or acquired as a result of other diseases.
A number of metabolic diseases may affect the chemical composition of urine thereby increasing the risk of kidney stone formation. These diseases may cause the following changes in the urine :
- High calcium levels in the urine – hypercalciuria.
- High uric acid levels in the urine – hyperuricosuria.
- High oxalate levels in the urine – hyperoxaluria.
- Low citrate levels in the urine – hypocitraturia.
- High sodium levels – hypernatriuria.
This is the medical term to refer to unknown causes and risks which may predispose a person to the formation of kidney stones.
Symptoms in Men, Women, Children
The symptoms associated with the presence of a kidney stone may not always be overt. In most cases it will remain unnoticed until it enters the ureter where the pain due to ureteral spasm, dilation and wall injury is severe. At other times, a small stone may pass out of the kidney with no symptoms. However, when the symptoms of a kidney stone is present, it can be excruciating to the point that daily functioning is affected.
Common Symptoms of Kidney Stones
- Kidney stone pain, known as renal colic, may present as severe pain in the flank, lower abdomen, back and/or groin.
- Blood in the urine.
- Dark, cloudy and/or foamy urine.
- Intense nausea with/without vomiting.
- Pain or burning when urinating.
- Frequent urination.
- Fever and chills if there is an infection.
Other symptoms may vary depending on the cause of the kidney stone and any other pre-existing conditions.
Not all the symptoms listed above may present at the same time. A large stone or multiple kidney stones may cause symptoms while it is within the kidney. However in most cases, patients only report to the emergency room once the kidney stone enters the ureter or causes an obstruction at the ureteropelvic junction (area where the ureter meets the kidney). Even the presence of blood in the urine usually goes unnoticed. Once the stone falls into the bladder, it once again may go unnoticed unless it is large and/or causes an obstruction.
The symptoms in both adults and children are almost the same. However, the presentation may differ depending on the individual, not only based on age and gender. Men are more likely to develop kidney stones than women and stones in children are rare. With kidney stone pain, the patient cannot lie still and is often pacing or writing in agony. It may extend from the lower part of the chest cavity, all the way to the upper part of the inner thigh.
If there is severely reduced urine output, inability to urinate (anuria) or significant abdominal swelling, it should be considered as a medical emergency and immediate treatment should be sought.
Symptoms in Men
- Pain extending to the groin – tip of penis, testicles.
- No swelling of the testicles present.
- Symptoms may be attributed to prostate enlargement (benign prostatic hyperplasia in older men) or inflammation/infection (prostatitis), cystitis, UTI, hernia, appendicitis.
Symptoms in Women
- Pain extending to the vulva.
- Itching of the vulva and discharge if active infection is present.
- Symptoms may be mistaken for ectopic pregnancy (if pregnant), ovulation/menstrual pain, cystitis, UTI, hernia, vaginitis.
Symptoms in Children, Baby
The symptoms in male or female children will not differ significantly from the symptoms mentioned above. In infants, a kidney stone may be easily missed because it is rare and the patient is unable to describe the symptoms.
Parents/caregivers of infants should be alerted to the :
- Restless and capricious child – constantly crying.
- Changes in urine output or color.
- Frequency of urination when compared to regular output (number of diapers soiled by urine).
These symptoms accompanied by a lack of appetite, gagging or vomiting or change in bowel movements (constipation or diarrhea) should raise the question of the possibility of a kidney/urinary stone.
Last updated on August 14, 2018.