There is a genetic predisposition, first-degree relatives have a great increase in the chance of VUR. The gene frequency is estimated to be 1:600. The American Academy of Pediatrics recommends that children from 2 to 24 months presenting with a UTI should be investigated for VUR.

In the general population, the frequency of medullary sponge kidney disease is reported to be 0.02–0.005%; that is, 1 in 5000 to 1 in 20,000. The frequency of medullary sponge kidney has been reported by various authors to be 1221% in patients with kidney stones. The disease is bilateral in 70% of cases.

This requires drainage, best performed by ureteral stent placement or nephrostomy.

There are roughly 12–13 cases annually per 10,000 population in women receiving outpatient treatment and 3–4 cases requiring admission. In men, 2–3 cases per 10,000 are treated as outpatients and 1– cases/10,000 require admission. Young women are most often affected, probably reflecting sexual activity in that age group. Infants and the elderly are also at increased risk, reflecting anatomical changes and hormonal status. Xanthogranulomatous pyelonephritis is most common in middle-aged women. It can present somewhat differently in children, in whom it may be mistaken for Wilms' tumor.

Complications associated with medullary sponge kidney include the following:

- Kidney stones

- Urinary tract infection (UTI)

- Blood in the urine

- Distal renal tubular acidosis (Type 1 RTA)

- Chronic kidney disease (rarely)

- Marked chronic pain

The kidneys are the only body system that are directly affected by tubulointerstitial nephritis. Kidney function is usually reduced; the kidneys can be just slightly dysfunctional, or fail completely.

In chronic tubulointerstitial nephritis, the most serious long-term effect is kidney failure. When the proximal tubule is injured, sodium, potassium, bicarbonate, uric acid, and phosphate reabsorption may be reduced or changed, resulting in low bicarbonate, known as metabolic acidosis, low potassium, low uric acid known as hypouricemia, and low phosphate known as hypophosphatemia. Damage to the distal tubule may cause loss of urine-concentrating ability and polyuria.

In most cases of acute tubulointerstitial nephritis, the function of the kidneys will return after the harmful drug is not taken anymore, or when the underlying disease is cured by treatment. If the illness is caused by an allergic reaction, a corticosteroid may speed the recovery kidney function; however, this is often not the case.

Chronic tubulointerstitial nephritis has no cure. Some patients may require dialysis. Eventually, a kidney transplant may be needed.

Pyonephrosis is sometimes a complication of kidney stones, which can be a source of persisting infection. It may also occur spontaneously. It can occur as a complication of hydronephrosis or pyelonephritis.

Common causes include infection, or reaction to medication such as an analgesic or antibiotics such as methicillin (meticillin). Reaction to medications causes 71% to 92% of cases.

This disease is also caused by other diseases and toxins that damage the kidney. Both acute and chronic tubulointerstitial nephritis can be caused by a bacterial infection in the kidneys known as pyelonephritis, but the most common cause is by an adverse reaction to a drug. The drugs that are known to cause this sort of reaction are antibiotics such as penicillin

and cephalexin, and nonsteroidal anti-inflammatory drugs (aspirin less frequently than others), as well as proton-pump inhibitors, rifampicin, sulfa drugs, fluoroquinolones, diuretics, allopurinol, and phenytoin. The time between exposure to the drug and the development of acute tubulointerstitial nephritis can be anywhere from 5 days to 5 months (fenoprofen induced).

Depending on the cause, a proportion of patients (5–10%) will never regain full kidney function, thus entering end-stage kidney failure and requiring lifelong dialysis or a kidney transplant. Patients with AKI are more likely to die prematurely after being discharged from hospital, even if their kidney function has recovered.

The risk of developing chronic kidney disease is increased (8.8-fold).

Most cases of "community-acquired" pyelonephritis are due to bowel organisms that enter the urinary tract. Common organisms are "E. coli" (70–80%) and "Enterococcus faecalis". Hospital-acquired infections may be due to coliform bacteria and enterococci, as well as other organisms uncommon in the community (e.g., "Pseudomonas aeruginosa" and various species of "Klebsiella"). Most cases of pyelonephritis start off as lower urinary tract infections, mainly cystitis and prostatitis. "E. coli" can invade the superficial umbrella cells of the bladder to form intracellular bacterial communities (IBCs), which can mature into biofilms. These biofilm-producing "E. coli" are resistant to antibiotic therapy and immune system responses, and present a possible explanation for recurrent urinary tract infections, including pyelonephritis. Risk is increased in the following situations:

- Mechanical: any structural abnormalities in the urinary tract, vesicoureteral reflux (urine from the bladder flowing back into the ureter), kidney stones, urinary tract catheterization, ureteral stents or drainage procedures (e.g., nephrostomy), pregnancy, neurogenic bladder (e.g., due to spinal cord damage, spina bifida or multiple sclerosis) and prostate disease (e.g., benign prostatic hyperplasia) in men

- Constitutional: diabetes mellitus, immunocompromised states

- Behavioral: change in sexual partner within the last year, spermicide use

- Positive family history (close family members with frequent urinary tract infections)

The pathophysiology of this condition can be due to analgesic nephropathy, which in turn is a result of long-term use of aspirin. It is a sequence of vascular occlusion, vasospasm, then infection and finally obstruction which leads to RPN.

Mortality after AKI remains high. Overall it is 20%, 30% if the patient is referred to nephrology, 50% if dialyzed, and 70% if on ICU.

If AKI develops after major surgery (13.4% of all people who have undergone major surgery) the risk of death is markedly increased (over 12-fold).

In terms of cause, almost any condition that involves ischemia can lead to renal papillary necrosis. A mnemonic for the causes of renal papillary necrosis is POSTCARDS: pyelonephritis, obstruction of the urogenital tract, sickle cell disease, tuberculosis, cirrhosis of the liver, analgesia/alcohol abuse, renal vein thrombosis, diabetes mellitus, and systemic vasculitis. Often, a patient with renal papillary necrosis will have numerous conditions acting synergistically to bring about the disease.

Analgesic nephropathy is a common cause of renal papillary necrosis. The damage is cumulative and most patients of renal papillary necrosis would have ingested at least 2 kg of analgesics in the past. The risk is higher for phenacetin (which was withdrawn from market in the United States) and paracetamol (acetaminophen) compared to aspirin and other NSAIDs.

Nephritis represents the ninth most common cause of death among all women in the US (and the fifth leading cause among non-Hispanic black women).

Worldwide the highest rates of nephritis are 50-55% for African or Asian descent, then Hispanic at 43% and Caucasian at 17%.

Renal tuberculosis

And other causes of hypercalcemia (and thus hypercalciuria)

- Immobilization (leading to hypercalcemia and hypercalciuria)

- Milk-alkali syndrome

- Hypervitaminosis D

- Multiple myeloma

Complications of analgesic nephropathy include pyelonephritis and end-stage kidney disease. Risk factors for poor prognosis include recurrent urinary tract infection and persistently elevated blood pressure. Analgesic nephropathy also appears to increase the risk of developing cancers of the urinary system.

In kidney stones, calcium oxalate is the most common mineral type (see Nephrolithiasis). Uric acid is the second most common mineral type, but an "in vitro" study showed uric acid stones and crystals can promote the formation of calcium oxalate stones.

Stones can cause disease by several mechanisms:

- Irritation of nearby tissues, causing pain, swelling, and inflammation

- Obstruction of an opening or duct, interfering with normal flow and disrupting the function of the organ in question

- Predisposition to infection (often due to disruption of normal flow)

A number of important medical conditions are caused by stones:

- Nephrolithiasis (kidney stones)

- Can cause hydronephrosis (swollen kidneys) and renal failure

- Can predispose to pyelonephritis (kidney infections)

- Can progress to urolithiasis

- Urolithiasis (urinary bladder stones)

- Can progress to bladder outlet obstruction

- Cholelithiasis (gallstones)

- Can predispose to cholecystitis (gall bladder infections) and ascending cholangitis (biliary tree infection)

- Can progress to choledocholithiasis (gallstones in the bile duct) and gallstone pancreatitis (inflammation of the pancreas)

- Gastric calculi can cause colic, obstruction, torsion, and necrosis.

Nephrocalcinosis Is connected with conditions that cause hypercalcemia, hyperphosphatemia, and the increased excretion of calcium, phosphate, and/or oxalate in the urine. A high urine pH can lead to Nephrocalcinosis. In conjustion with Nephrocalcinosis, hypercalcemia and hypercalciuria the following can occur:

- Primary hyperparathyroidism: Nephrocalcinosis is one of the most common symptoms of primary hyperparathyroidism.

- Sarcoidosis: Nephrocalcinosis is one of the most common symptoms.

- Vitamin D therapy: This can cause nephrocalcinosis because of Vitamin D therapy becauseit increase the absorption of ingested calcium and bone resorption, resulting in hypercalcemia and hypercalciuria.

Reflux nephropathy is kidney damage (nephropathy) due to urine flowing backward (reflux) from the bladder toward the kidneys; the latter is called vesicoureteral reflux (VUR). Longstanding VUR can result in small and scarred kidneys during the first five years of life in affected children. The end results of reflux nephropathy can include high blood pressure, excessive protein loss in the urine, and eventually kidney failure.

When reflux nephropathy is suspected as a cause of kidney disease, other conditions to consider include chronic pyelonephritis, obstructive uropathy, and analgesic overuse.

The term "reflux nephropathy" was introduced in 1973.

Treatment/management of nephritis depends on what has provoked the inflammation of the kidney(s). In the case of lupus nephritis, hydroxychloroquine could be used.

Despite expensive treatments, lupus nephritis remains a major cause of morbidity and mortality in people with relapsing or refractory lupus nephritis.

Cortical necrosis is a severe and life-threatening condition, with mortality rates over 50%. Those mortality rates are even higher in neonates with the condition due to the overall difficult nature of neonatal care and an increased frequency of comorbid conditions. The extent of the necrosis is a major determinant of the prognosis, which in turn is dependent on the duration of ischemia, duration of oliguria, and the severity of the precipitating conditions. Of those that survive the initial event, there are varying degrees of recovery possible, depending on the extent of the damage.

The long-term use of lithium, a medication commonly used to treat bipolar disorder and schizoaffective disorders, is known to cause nephropathy.

Urinary tract infections are more concerning in pregnancy due to the increased risk of kidney infections. During pregnancy, high progesterone levels elevate the risk of decreased muscle tone of the ureters and bladder, which leads to a greater likelihood of reflux, where urine flows back up the ureters and towards the kidneys. While pregnant women do not have an increased risk of asymptomatic bacteriuria, if bacteriuria is present they do have a 25–40% risk of a kidney infection. Thus if urine testing shows signs of an infection—even in the absence of symptoms—treatment is recommended. Cephalexin or nitrofurantoin are typically used because they are generally considered safe in pregnancy. A kidney infection during pregnancy may result in premature birth or pre-eclampsia (a state of high blood pressure and kidney dysfunction during pregnancy that can lead to seizures). Some women have UTIs that keep coming back in pregnancy and currently there is not enough research on how to best treat these infections.