When the urine becomes too concentrated, calcium, uric acid salts and other chemicals dissolved in the urine can crystallize, forming a kidney stone.
The urinary tract includes the kidneys, ureters, bladder and urethra. Within each kidney, urine flows from the outer cortex to the inner medulla. The renal pelvis is the funnel through which urine exits the kidney and enters the ureter. As urine can become very concentrated as it passes through the kidneys.
When the urine becomes too concentrated, calcium, uric acid salts and other chemicals dissolved in the urine can crystallize, forming a kidney stone (renal calculus).
Kidney stone disease, also known as urolithiasis, is when a solid piece of material (kidney stone) occurs in the urinary tract. Kidney stones typically form in the kidney and leave the body in the urine stream. A small stone may pass without causing symptoms. If a stone grows to more than 5 millimetres (0.2 in) it can cause blockage of the ureter resulting in severe pain in the lower back or abdomen. A stone may also result in blood in the urine, vomiting, or painful urination. About half of people will have another stone within ten years.
Between 1% and 15% of people globally are affected by kidney stones at some point in their lives. In 2015, 22.1 million cases occurred, resulting in about 16,100 deaths. They have become more common in the Western world since the 1970s. Generally, more men are affected than women. Kidney stones have affected humans throughout history with descriptions of surgery to remove them dating from as early as 600 BC.
Signs and symptoms
The hallmark of a stone that obstructs the ureter or renal pelvis is excruciating, intermittent pain that radiates from the flank to the groin or to the inner thigh. This pain, known as renal colic, is often described as one of the strongest pain sensations known. Renal colic caused by kidney stones is commonly accompanied by urinary urgency, restlessness, hematuria, sweating, nausea, and vomiting. It typically comes in waves lasting 20 to 60 minutes caused by peristaltic contractions of the ureter as it attempts to expel the stone. The embryological link between the urinary tract, the genital system, and the gastrointestinal tract is the basis of the radiation of pain to the gonads, as well as nausea and vomiting which are also common in urolithiasis. Postrenal azotemia and hydronephrosis can be observed following the obstruction of urine flow through one or both ureters.
Pain in the lower-left quadrant can sometimes be confused with diverticulitis because the sigmoid colon overlaps the ureter, and the exact location of the pain may be difficult to isolate due to the close proximity of these two structures.
Risk factors
Dehydration from the low fluid intake is a major factor in stone formation. Obesity is a leading risk factor as well. High dietary intake of animal protein, sodium, and sugars including honey, refined sugars, fructose and high fructose corn syrup, oxalate, grapefruit juice, and apple juice may increase the risk of kidney stone formation.
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