OVERVIEW

What is the renal pelvis?

The renal pelvis is a part of the kidney, forming a sac-like dilation at the upper end of the ureter and belonging to the upper urinary tract. Urine from numerous nephrons collects in the renal pelvis and is then discharged into the bladder through the ureter.

What is pyelonephritis?

Pyelonephritis is an infectious disease of the renal pelvis, which can be classified into acute and chronic forms based on the onset and progression:

• Acute pyelonephritis is an infection of the renal pelvis and renal parenchyma, categorized as an upper urinary tract infection. It is often caused by Escherichia coli (E. coli). Pathogens typically ascend from the urethra, infecting the renal pelvis and even the renal parenchyma.

• Chronic pyelonephritis refers to chronic inflammation of the renal pelvis and calyces. In addition to infection symptoms, it may involve renal interstitial damage, deformation of the renal pelvis and calyces, scarring of the renal cortex and renal papillae, leading to renal dysfunction and chronic renal failure.

Is pyelonephritis common?

Acute pyelonephritis is relatively common, whereas chronic pyelonephritis is less frequent. Overall, pyelonephritis is more prevalent in women, and pregnancy can increase the risk of the disease.

Are pyelonephritis and nephritis the same condition?

No, they are not the same. Pyelonephritis is an infectious disease, and most patients can fully recover with antibiotic treatment. In contrast, nephritis may be an autoimmune disorder, often requiring immunosuppressive therapy such as corticosteroids, and it is generally harder to cure completely.

SYMPTOMS

What are the common manifestations of pyelonephritis?

Acute pyelonephritis may initially present with bladder irritation symptoms such as frequent urination, urgency, and dysuria, followed by lower back pain, hematuria, high fever, and chills. It may also be accompanied by systemic symptoms like headache, body aches, nausea, and vomiting. Note: Systemic symptoms are prominent in acute pyelonephritis.

Chronic pyelonephritis has complex manifestations, often presenting as dull lower back pain and increased nocturia, possibly accompanied by low-grade fever, fatigue, and loss of appetite. During acute episodes, symptoms resemble those of acute pyelonephritis. As the disease progresses, it may develop into chronic renal failure, manifesting as oliguria, edema, etc. Note: Imaging studies in chronic pyelonephritis may reveal calyceal atrophy and degeneration.

What are the consequences of untreated pyelonephritis?

Untreated pyelonephritis may lead to the following complications:

• Renal papillary necrosis: Often occurs in patients with diabetes or urinary tract obstruction (e.g., urinary stones) and is a severe complication. Symptoms may include high fever, chills, severe lower back or abdominal pain, and hematuria. Intravenous pyelography can confirm the diagnosis.

• Renal abscess and perinephric abscess: Also common in patients with diabetes or urinary tract obstruction (e.g., urinary stones). It typically presents as unilateral lower back pain that worsens when bending toward the unaffected side. Diagnosis can be made via ultrasound.

• Sepsis: A life-threatening condition characterized by sudden chills, high fever, and shock, with a mortality rate as high as 50%.

• Infection stones: If the pathogen causing pyelonephritis is Proteus, it may lead to infection stones, increasing the difficulty of antibiotic treatment and causing urinary tract obstruction, further damaging the kidneys.

• Acute kidney injury: Presents as reduced urine output, elevated serum creatinine, and electrolyte imbalances. Severe cases may require hemodialysis.

CAUSES

What causes pyelonephritis?

Bacterial infection is the most common cause of pyelonephritis, with about 90% of cases caused by Escherichia coli, followed by Proteus and Klebsiella. A small number are caused by Enterococcus faecalis, Staphylococcus citreus, and Staphylococcus albus. Pathogens usually ascend from the urethra, infecting the renal pelvis and even the renal parenchyma.

Who is more likely to develop pyelonephritis?

Pyelonephritis is more common in patients with predisposing factors, including:

• Urinary tract obstruction, such as urinary stones, urological tumors, benign prostatic hyperplasia, or urethral malformations.

• Immunocompromised conditions, such as diabetes, severe chronic diseases, or HIV/AIDS.

Why is pyelonephritis more common in women?

Women have a shorter (about 4 cm) and wider urethra, with the urethral opening closer to the anus, making it easier for pathogens to invade. After entering the urethra, pathogens ascend and cause infection in the renal pelvis.

Is pyelonephritis contagious?

Pyelonephritis is not contagious.

Why does pyelonephritis recur easily?

Patients with urinary tract obstruction or weakened immunity who do not receive timely treatment are prone to recurrent infections. Therefore, patients with urinary stones should remove them as early as possible, and those with high blood sugar should actively control their glucose levels.

DIAGNOSIS

What tests are needed to diagnose pyelonephritis? What precautions should be taken?

If pyelonephritis is suspected, the doctor will first conduct a detailed medical history inquiry and physical examination. Additionally, the following tests are usually required:

• Urinalysis: The presence of numerous white blood cells in the urinalysis is significant for diagnosing urinary tract infections. If white blood cell casts are detected, it further suggests pyelonephritis rather than a lower urinary tract infection (which typically refers to cystitis or urethritis).

• Urine culture: This is mainly performed to identify the pathogen and guide treatment.

• Complete blood count (CBC) and high-sensitivity C-reactive protein (hs-CRP): These tests reflect the presence and severity of systemic infection. Elevated white blood cell counts and hs-CRP levels indicate a more severe infection.

• Renal function tests: These assess whether kidney damage has occurred.

• Urinary tract ultrasound: This helps evaluate the urinary tract for predisposing factors such as stones, structural abnormalities, reflux, or masses.

• Intravenous pyelography (IVP): This is particularly useful for diagnosing chronic pyelonephritis and detecting renal papillary necrosis. It is also recommended for patients with poor treatment responses.

• For urinalysis and urine culture, a midstream urine sample is recommended—collecting only the middle portion of the urine stream, not the initial or final parts.

• A full bladder is required for the urinary tract ultrasound to facilitate better observation by the doctor.

What diseases can pyelonephritis be easily confused with?

• Acute cystitis: As a lower urinary tract infection, acute cystitis primarily presents with bladder irritation symptoms such as frequent urination, urgency, and dysuria. It usually does not cause high fever, chills, or back pain.

• Kidney stones: These often manifest as severe unilateral flank pain but without high fever or chills. An ultrasound can help differentiate between the two.

• Urethritis: As a lower urinary tract infection, urethritis mainly causes mild dysuria and tends to recur. It is more common in women and is not accompanied by high fever, chills, or back pain.

TREATMENT

Which department should I visit for pyelonephritis?

It is recommended to see a nephrologist.

How is pyelonephritis treated?

• For mild cases without systemic symptoms such as headache, body aches, nausea, or vomiting: Oral antibiotics (e.g., penicillin, cephalosporins, or quinolones) can be prescribed on an outpatient basis for 10–14 days.

• For severe cases with systemic symptoms: Hospitalization and intravenous antibiotic therapy are recommended. The same antibiotics may be used, and combination therapy may be necessary if required. After fever subsides, continue treatment for 3 days, then switch to oral antibiotics for an additional 2 weeks.
  Treatment for chronic pyelonephritis:
  During acute episodes, follow the same approach as acute pyelonephritis. During remission, identify and eliminate predisposing factors to prevent recurrence.

Can pyelonephritis be cured?

Theoretically, 90% of acute pyelonephritis cases can be cured. Refractory acute or chronic pyelonephritis often involves predisposing factors, and cure is possible only after addressing these factors.

When can antibiotics be stopped for acute pyelonephritis?

• For mild cases: Antibiotics can be discontinued after about 2 weeks if symptoms improve.

• For cases with systemic symptoms: Continue intravenous antibiotics for 3 days after fever subsides, then switch to oral antibiotics for 2 weeks before stopping.

• If urine culture remains positive after treatment, continue antibiotic therapy for 4–6 weeks based on sensitivity testing.

What are the common side effects of pyelonephritis medications?

The most common side effects of antibiotics are gastrointestinal reactions, such as nausea, vomiting, diarrhea, constipation, or abdominal discomfort, which usually resolve after discontinuation. Penicillins require a skin test due to the risk of allergic reactions.

Are there any long-term complications after pyelonephritis treatment?

Generally, no complications remain after recovery.

Is follow-up needed after pyelonephritis treatment? How?

Regular follow-up is necessary. Initially, check urine tests weekly for the first 3 months and urine cultures every 2 weeks. If no abnormalities persist, urine tests can be done every 6 months.

Is pyelonephritis prone to recurrence?

Yes, especially in patients with diabetes, severe chronic illnesses, AIDS, or other conditions that weaken immunity.

How is pyelonephritis treated during pregnancy?

Pyelonephritis during pregnancy requires prompt treatment to prevent serious effects on both mother and fetus. Intravenous penicillin is the preferred antibiotic; quinolones are contraindicated.

DIET & LIFESTYLE

What should be noted in the diet for pyelonephritis?

There are no special dietary restrictions. However, a healthy diet is beneficial for everyone:

• Eat more fruits and vegetables; maintain a balanced diet with both meat and vegetables. If you are vegetarian, consume more soy products to supplement protein. If you can drink milk, ensure 300 mL daily to avoid calcium deficiency.

• Avoid relying solely on refined rice and wheat for staple foods. Replace some with legumes, potatoes, pumpkin, etc.

• Use less salt and high-sodium seasonings when cooking.

• Limit intake of pickled vegetables and meats.

• Avoid alcohol as much as possible.

What should be noted in daily life for pyelonephritis?

Drink plenty of water, avoid holding urine for long periods, and actively control blood sugar if you have diabetes. Maintain personal hygiene by washing hands frequently and changing underwear regularly. Engage in moderate exercise to boost immunity.

Does pyelonephritis affect fertility?

After being cured, pyelonephritis has no impact on fertility.

PREVENTION

How to prevent the occurrence and recurrence of pyelonephritis?

The key is to eliminate or control predisposing factors, including:

• Actively addressing obstructive factors, such as treating urinary stones, urinary tract tumors, and urinary tract obstructions.

• Diabetic patients should maintain good blood sugar control. Patients with chronic diseases or AIDS should actively manage their underlying conditions.

• Avoid long-term indwelling catheters.

• Prophylactic antibiotics may be used after invasive procedures such as cystoscopy or urinary lithotripsy.

How to prevent other serious complications of pyelonephritis?

Seek medical attention early if symptoms like frequent urination, urgency, dysuria, back pain, or fever occur. Strictly follow the doctor's medication instructions, complete the full course of treatment, and avoid discontinuing medication arbitrarily.