Nephritic syndrome is a pattern of kidney problems caused by inflammation in the tiny filters of your kidneys, called glomeruli. It typically shows up as blood in the urine, high blood pressure, swelling, and reduced urine output. Unlike some kidney conditions that develop slowly, nephritic syndrome often appears suddenly, sometimes within days of the triggering event.
What Happens Inside the Kidney
Your kidneys contain roughly one million microscopic filtering units. Each one has a cluster of tiny blood vessels called a glomerulus, surrounded by a thin membrane that acts like a sieve. In healthy kidneys, this membrane lets water and waste pass through into the urine while keeping blood cells and most proteins in the bloodstream.
In nephritic syndrome, the immune system deposits clumps of antibodies (called immune complexes) along this membrane. The body’s own blood vessel cells actively transport these immune complexes from the capillaries into surrounding tissue, where immune cells detect them. Those immune cells then release inflammatory signals that pull even more white blood cells into the kidney. The result is swelling, damage, and tiny holes in the membrane that let blood cells and protein leak through into the urine. At the same time, the inflamed glomeruli can’t filter as efficiently, so waste products build up in the blood and your body retains extra salt and water.
Recognizable Symptoms
The hallmark of nephritic syndrome is blood in the urine. It doesn’t always look bright red. More often, urine turns dark, tea-colored, or cloudy because damaged blood vessels in the kidney leak red blood cells in small amounts. You may also notice that you’re producing less urine than normal, or in severe cases, very little at all.
Swelling is common, particularly around the face, eyelids, hands, and feet. This happens because damaged glomeruli let a blood protein called albumin escape into the urine. Albumin normally keeps fluid inside your blood vessels, so when levels drop, fluid shifts into surrounding tissues. High blood pressure develops because the kidneys hold onto sodium and water they would normally filter out, increasing the volume of fluid in your circulatory system.
Most Common Causes
The single most common trigger, especially in children, is a recent strep infection. This condition, called post-streptococcal glomerulonephritis, doesn’t happen during the infection itself but after a delay. Following a strep throat, nephritic symptoms typically appear about 10 days later. After a strep skin infection, the gap is longer, up to three weeks. The immune complexes formed during the fight against the bacteria end up lodged in the kidney’s filters, setting off inflammation even after the infection has cleared.
IgA nephropathy (sometimes called Berger’s disease) is another frequent cause and the most common form of glomerulonephritis worldwide. In this condition, an abnormal form of the antibody IgA accumulates in the kidney’s filtering membranes. The classic presentation is visible blood in the urine that appears at the same time as a cold, flu, or other upper respiratory infection, rather than after a delay. Many people with IgA deposits in their kidneys have no symptoms at all. Studies of organ donors and autopsy findings show that silent IgA deposits exist in roughly 7 to 16 percent of the general population, depending on geographic region.
Other causes include lupus, certain types of vasculitis (conditions where the immune system attacks blood vessel walls), and infections like hepatitis B or C. In some cases, the immune attack targets the kidney’s basement membrane directly, a condition that can progress rapidly.
How It Differs From Nephrotic Syndrome
Nephritic and nephrotic syndrome sound almost identical but represent different patterns of kidney damage. Nephritic syndrome is driven by inflammation. The defining features are blood in the urine, high blood pressure, and moderate protein loss. Nephrotic syndrome, by contrast, involves massive protein loss into the urine (generally more than 3.5 grams per day in adults) with severe swelling but usually no blood in the urine and normal blood pressure early on.
In practice, some overlap exists. A person with nephritic syndrome can still lose significant protein, and some conditions can present with features of both. But the presence of blood and red blood cell casts in the urine points strongly toward a nephritic process.
How It Is Diagnosed
A urine sample is the starting point. Under a microscope, nephritic urine reveals red blood cells that look misshapen, called dysmorphic red blood cells. These cells get distorted as they squeeze through the damaged glomerular membrane. When dysmorphic cells make up more than 75 percent of the red blood cells in a sample, it’s a strong indicator the bleeding originates in the kidney rather than somewhere else in the urinary tract, like the bladder. If fewer than 17 percent are dysmorphic, the bleeding is more likely from a non-kidney source.
Red blood cell casts are another important finding. These are clusters of red blood cells that clump together inside the kidney’s tiny tubules and get flushed out in the urine. Their presence is essentially a fingerprint of glomerular inflammation. Blood tests check kidney function by measuring waste products that should be filtered out, along with markers of immune activity like complement levels and specific antibodies that can point to the underlying cause.
A kidney biopsy provides the definitive diagnosis. A small tissue sample examined under a microscope reveals the pattern and severity of inflammation, the location of immune deposits, and whether the damage is likely reversible. This information directly shapes treatment decisions.
When It Becomes Dangerous
Most cases of post-streptococcal nephritic syndrome, particularly in children, resolve on their own. But some forms of nephritic syndrome can escalate into a condition called rapidly progressive glomerulonephritis, or RPGN. In RPGN, inflammatory cells pile up inside the glomerular capsule and form crescent-shaped masses that compress and destroy the filtering structure. When more than half the glomeruli in a biopsy sample show these crescents, kidney function can decline from normal to failure in a matter of weeks to months without treatment.
RPGN is a medical emergency. It can arise from several different immune mechanisms, and identifying which one is driving it determines the treatment approach. The key warning signs are a rapid drop in urine output, fast-rising blood pressure, and significant fluid retention that worsens over days rather than stabilizing.
Treatment and Recovery
Treatment depends entirely on the underlying cause and severity. For post-streptococcal cases, the main approach is supportive care while the inflammation runs its course. This means managing blood pressure, reducing fluid overload, and restricting sodium intake to help control swelling. Typical sodium limits range from 2,000 to 4,000 milligrams per day. That means avoiding added salt during cooking and at the table, limiting high-sodium condiments to about a tablespoon per meal, and watching for hidden sodium in drinks like sports beverages and sodas.
For immune-driven causes like lupus nephritis, IgA nephropathy, or RPGN, treatment targets the overactive immune response. The specifics vary by condition and severity, but the goal is to suppress the inflammatory process before it causes permanent scarring.
Recovery timelines vary widely. Children with post-streptococcal disease typically recover well. Blood in the urine usually clears within weeks, though trace amounts of protein in the urine can persist for months. In IgA nephropathy, kidney function after an acute flare usually bounces back within one to two weeks after visible blood in the urine disappears, but the underlying condition requires long-term monitoring.
Long-Term Monitoring
Even after symptoms improve, follow-up matters. Urine testing should continue for at least 6 months and ideally 12 months from the initial episode to catch any signs of ongoing or recurring inflammation. Most people who develop a secondary complication like worsening kidney function will show signs within the first three months, but delayed problems can emerge later. Monitoring typically involves periodic urine tests checking for blood and protein, along with blood tests measuring how well the kidneys are filtering waste. The frequency of testing tapers over time if results remain stable, but anyone who has had nephritic syndrome carries a slightly higher lifetime risk of chronic kidney problems, making periodic checkups worthwhile even years later.