Postinfectious glomerulonephritis is a kidney condition that appears after the body has resolved an infection. It is not an infection of the kidneys themselves, but an inflammatory reaction within the kidneys’ filtering system. This condition signifies inflammation of the glomeruli, the microscopic structures responsible for filtering waste and excess fluid from the blood. The issue stems from the body’s own immune response to a prior infection, which inadvertently causes inflammation and damages these filters.
Underlying Causes and Immune Response
The onset of postinfectious glomerulonephritis (PIGN) is most frequently linked to a preceding infection with specific strains of Group A streptococcus bacteria. These are the same bacteria responsible for strep throat or skin infections such as impetigo. The condition develops with a characteristic delay of one to two weeks following a throat infection and three to six weeks after a skin infection, once the initial infection has been fought off. Other bacterial, viral, or fungal infections can also trigger a similar response.
The underlying mechanism involves the body’s immune system. During an infection, the immune system produces antibodies to target invading germs, or antigens. These antibodies bind to the antigens, forming antigen-antibody complexes that can continue to circulate in the bloodstream after the infection.
These circulating complexes can become lodged in the intricate capillary loops of the glomeruli. This deposition acts as a trigger, initiating an inflammatory cascade. The body’s complement system is activated, leading to an influx of inflammatory cells that cause swelling and damage, impairing the kidneys’ ability to filter blood effectively, much like a fine-mesh sieve becoming clogged with debris.
Recognizing the Signs and Symptoms
The signs of PIGN appear weeks after the initial infection has passed. One of the most common symptoms is edema, which is swelling caused by fluid retention. This presents as puffiness around the eyes, particularly in the morning, and can also affect the hands, feet, and ankles.
Another distinct indicator is a change in the urine’s appearance. Damage to the glomeruli allows red blood cells to leak from the bloodstream into the urine, a condition known as hematuria. This can cause the urine to take on a dark, brownish hue, described as looking like tea or cola. In many cases, the amount of blood is microscopic and not visible to the naked eye.
Alongside these signs, individuals may experience a noticeable decrease in urine output, a condition called oliguria. This fluid retention can also contribute to the development of new or worsened high blood pressure (hypertension). General feelings of fatigue or a loss of appetite may also accompany the more specific symptoms.
The Diagnostic Workup
Confirming a diagnosis of PIGN begins with a thorough evaluation of the patient’s recent health. A doctor will inquire about any recent infections, particularly sore throats or skin sores, to establish a timeline. The physical examination focuses on identifying signs such as swelling and measuring blood pressure.
A urinalysis examines a urine sample for abnormalities that point toward glomerular inflammation. The presence of red blood cells (hematuria), protein (proteinuria), and red blood cell casts—microscopic structures formed in the kidneys—are indicators of glomerular damage.
Blood tests provide further evidence. These tests measure levels of waste products like blood urea nitrogen (BUN) and creatinine, which are elevated when kidney function is impaired. To confirm a recent streptococcal infection, doctors test for antibodies against the bacteria, such as the antistreptolysin O (ASO) titer. Another blood test measures complement levels (C3), which are low as the complement system is consumed during the inflammatory process.
In most cases, especially in children with this classic presentation, a diagnosis can be made without more invasive procedures. A kidney biopsy, where a small piece of kidney tissue is removed for examination, is reserved for adults, atypical cases, or situations where symptoms do not resolve as expected, to rule out other forms of kidney disease.
Treatment and Symptom Management
Treatment for PIGN is primarily supportive, as there is no specific therapy that directly reverses the glomerular inflammation. The main goal is to manage the symptoms and complications while the kidneys are given time to heal on their own.
To address fluid overload and edema, physicians prescribe diuretics. These medications help the kidneys remove excess salt and water from the body, which reduces swelling and helps lower blood pressure. If hypertension persists, specific blood pressure medications may also be used to bring it under control.
Dietary modifications are an important component of management. A low-sodium diet is implemented to help control fluid retention and high blood pressure. Depending on the severity of kidney dysfunction, doctors may also recommend limiting the intake of potassium and protein to reduce the workload on the healing kidneys.
While antibiotics do not treat the existing kidney inflammation, they are often prescribed to ensure that any lingering bacteria from the initial infection are completely eliminated. For instance, if the PIGN was triggered by strep throat, a course of penicillin might be given. This step is important to prevent the spread of the infection and stop any ongoing stimulation of the immune system.
Recovery and Long-Term Outlook
The prognosis for children with PIGN is excellent, as the vast majority of pediatric patients experience a full recovery of kidney function. The acute symptoms, such as significant swelling and high blood pressure, begin to improve within a few weeks as the inflammation subsides.
While the most apparent symptoms resolve relatively quickly, microscopic amounts of blood or protein can be detectable in the urine for several months to even a year or two after the illness. Regular follow-up appointments are scheduled to monitor these levels and ensure they are gradually returning to normal, confirming that the kidneys have fully healed.
For adults, the long-term outlook can be more varied. While many adults also recover completely, a higher proportion may experience lasting complications compared to children. A minority of adult patients may go on to develop chronic kidney disease (CKD), persistent proteinuria, or long-term hypertension.
Because of this risk, long-term monitoring of kidney function and blood pressure is important for adults who have had PIGN.