In short

Focal segmental glomerulosclerosis (FSGS) is a kidney disease that develops when scarring damages the tiny filters in your kidneys, making it harder for them to remove waste from your blood. Because symptoms can be subtle or appear during routine tests, understanding how doctors diagnose this condition is an important step in getting proper care and treatment.

Key points

FSGS often has no obvious symptoms at first and is frequently discovered during routine medical exams through abnormal blood or urine tests, highlighting the importance of regular health checkups.
Foamy or bubbly urine is a telltale sign that protein is leaking into your urine and should prompt you to see a doctor for kidney testing.
A kidney biopsy is the only way to definitively diagnose FSGS and distinguish it from other kidney diseases, making this procedure essential despite being more invasive than blood or urine tests.
The amount of protein in your urine is one of the most important indicators of disease severity and helps predict how FSGS will progress over time.
Genetic testing can reveal inherited forms of FSGS and provide crucial information about treatment response and transplant outcomes, especially for people with family history of kidney disease.
Clinical trials testing new FSGS treatments require extensive diagnostic testing to confirm eligibility, but participation offers potential access to innovative therapies not yet widely available.
FSGS can recur in 30-40% of transplanted kidneys, but people with genetic forms have much lower recurrence risk, making accurate diagnosis of FSGS type critically important for transplant planning.
People of African ancestry face higher FSGS risk due to APOL1 gene variants, which can be identified through genetic testing and may influence treatment strategies.

Introduction: Who Should Seek Diagnostic Testing

Not everyone with FSGS knows something is wrong right away. Many people discover they have this condition during a routine physical exam or when testing for other health issues. Healthcare providers often find the first signs of FSGS when lab results show unusual levels of protein in the urine or changes in kidney function.

You should consider seeking medical evaluation if you notice certain warning signs. Swelling in your legs, ankles, feet, or around your eyes is one of the most common symptoms that brings people to their doctor. This swelling, called edema, happens when your kidneys cannot properly remove extra fluid from your body. Other signs include foamy or bubbly urine, which indicates protein is leaking into your urine, sudden weight gain from fluid buildup, extreme tiredness, or loss of appetite.

People with certain risk factors should be particularly vigilant about kidney health. If you have a family history of FSGS, you may carry genetic changes that increase your risk. African ancestry is another important risk factor, as FSGS is diagnosed more often in people who are Black. Other conditions that increase your chance of developing FSGS include obesity, viral infections such as HIV, sickle cell disease, or low birth weight.

High blood pressure is both a symptom and a complication of FSGS. Some people with FSGS develop severe hypertension, with blood pressure readings that can be dangerously high. If your doctor finds elevated blood pressure along with other signs of kidney problems, they will likely recommend further testing.

Children and adults can both develop FSGS, though it affects different age groups in different ways. In children, FSGS accounts for about 20% of cases of nephrotic syndrome, a condition where the kidneys release too much protein into the urine. In adults, this percentage rises to 40%, making FSGS one of the most common causes of nephrotic syndrome.

Classic Diagnostic Methods

Diagnosing FSGS requires multiple steps because the condition cannot be identified through symptoms alone. Your doctor will start with a thorough review of your medical history, asking about family health history, current medications, any recent infections, and symptoms you may have noticed. A physical examination follows, where your healthcare provider checks for signs of fluid retention, measures your blood pressure, and looks for other indicators of kidney disease.

Urine Tests

One of the first and most important tests for FSGS is a urine test. Your doctor may ask you to provide a single urine sample or collect all your urine over a 24-hour period. These tests measure how much protein is present in your urine, a condition called proteinuria. In healthy kidneys, very little protein escapes into the urine because the glomeruli act as effective filters. When FSGS damages these filters, large amounts of protein leak through.

The 24-hour urine collection gives doctors a more complete picture of protein loss throughout the day and night. When protein levels reach 3 grams or more per day, doctors describe this as nephrotic-range proteinuria. More than 70% of adults newly diagnosed with primary FSGS have proteinuria in this nephrotic range, which indicates significant kidney damage.

Urine tests also check for other abnormalities. Your doctor may look for casts, which are tiny tube-shaped structures made of protein and cells that form in the kidney tubules. The presence of certain types of casts can provide clues about what is happening inside your kidneys.

Blood Tests

Blood tests reveal how well your kidneys are working and detect problems caused by FSGS. One crucial blood test measures your glomerular filtration rate (GFR), which tells doctors how effectively your kidneys are filtering waste from your blood. A declining GFR indicates worsening kidney function. Normal GFR varies by age, but a significant drop below expected levels signals kidney damage.

Your healthcare provider will also check the level of albumin in your blood. Albumin is an important protein that should remain in your bloodstream, not leak into your urine. People with FSGS typically have low serum albumin levels, called hypoalbuminemia, because so much protein is being lost through damaged kidneys. When albumin drops below 3.5 grams per deciliter, it contributes to the fluid retention and swelling characteristic of nephrotic syndrome.

Other blood tests examine cholesterol levels, which are often elevated in people with FSGS, and look at electrolytes and other markers of kidney health. These tests help doctors understand the full impact of the disease on your body.

Kidney Imaging

Imaging tests help doctors see the size and shape of your kidneys and rule out other problems. An ultrasound uses sound waves to create pictures of your kidneys without using radiation. This safe, painless test can show whether your kidneys are normal in size or have shrunk, which might happen with chronic kidney damage. CT scans or MRI scans may also be ordered to provide more detailed images if needed.

While imaging tests are useful for assessing overall kidney structure, they cannot show the microscopic changes that define FSGS. These tests help doctors rule out other causes of kidney problems, such as kidney stones, cysts, or tumors, and prepare for the kidney biopsy procedure.

Kidney Biopsy

A kidney biopsy is the only way to definitively diagnose FSGS. During this procedure, a doctor inserts a thin needle through your skin into your kidney to remove a small sample of kidney tissue. The procedure is usually done with local anesthesia to numb the area, and imaging guidance such as ultrasound helps the doctor place the needle accurately.

The tissue sample is then examined under a microscope by a specialist called a pathologist. In FSGS, the pathologist looks for specific patterns of scarring. The name of the disease describes what they see: "focal" means only some of the glomeruli show damage, not all of them; "segmental" means only part of each affected glomerulus is scarred, not the entire structure; and "glomerulosclerosis" refers to the hardening and scarring of the glomeruli themselves.

The biopsy results do more than confirm FSGS. They also help doctors understand what type of FSGS you have and how severe the damage is. There are different patterns of scarring visible under the microscope, and these patterns can provide information about prognosis and guide treatment decisions. The biopsy can also reveal whether the FSGS is primary, where no underlying cause is found, or secondary to another condition such as an infection or drug toxicity.

After a kidney biopsy, you will need to rest and avoid strenuous activity for a period of time. Some people experience minor discomfort or see a small amount of blood in their urine afterward, but serious complications are rare. Your healthcare team will monitor you closely after the procedure to ensure proper healing.

Genetic Testing

In some cases, particularly when FSGS runs in families or appears in young people, doctors may recommend genetic testing. This involves a blood test to look for specific genetic changes, or mutations, that can cause FSGS. Certain genetic variants, such as those in the APOL1 gene, are associated with increased risk of developing FSGS and may affect how the disease progresses and responds to treatment.

Genetic testing is especially valuable for families where multiple members have kidney disease. If a genetic cause is identified, it can help predict whether FSGS might recur after a kidney transplant and guide family planning decisions. People with genetic forms of FSGS typically do not respond well to medications that suppress the immune system, so knowing the genetic cause can save time and avoid unnecessary treatment side effects.

Diagnostics for Clinical Trial Qualification

Clinical trials are research studies that test new treatments for FSGS. These trials offer hope for better therapies, especially for people whose disease does not respond to currently available treatments. However, getting into a clinical trial requires meeting specific criteria, and diagnostic tests play a crucial role in determining eligibility.

Before you can enroll in a clinical trial, researchers need to confirm your diagnosis and gather detailed information about your disease. A confirmed diagnosis by kidney biopsy is typically required. The biopsy report must show the characteristic pattern of focal segmental glomerulosclerosis and rule out other types of kidney disease that might look similar clinically but have different causes.

Clinical trials for FSGS often focus on patients with primary FSGS who have proteinuria in the nephrotic range. Researchers measure your baseline protein levels carefully because one of the main goals of new treatments is to reduce proteinuria. Many trials require that your 24-hour urine protein exceeds a certain threshold, such as 3 grams per day, to qualify for enrollment. They also measure your glomerular filtration rate to assess your current level of kidney function.

Some clinical trials may require genetic testing results, particularly studies testing precision therapies targeted to specific genetic mutations. If you have already had genetic testing that identified variants associated with FSGS, this information helps researchers match you with appropriate trials. Conversely, some trials specifically exclude genetic forms of FSGS because they are testing immunosuppressive drugs that only work in non-genetic cases.

Blood pressure measurements are standard for trial enrollment. Because FSGS commonly causes hypertension, researchers need to know your blood pressure at baseline and whether you are taking medications to control it. Some trials test drugs that affect blood pressure, so your cardiovascular status must be carefully documented.

Clinical trials may also look at specific biomarkers in your blood or urine. Researchers are working to identify proteins or other molecules that can predict how well someone will respond to treatment or how quickly their disease will progress. If a trial is testing a drug aimed at a specific biological pathway, you may need testing to show that pathway is active in your disease.

Imaging studies such as ultrasounds or CT scans may be required before trial enrollment to establish baseline kidney size and structure. These imaging studies will be repeated during the trial to monitor any changes. The goal is to see whether the experimental treatment prevents further kidney damage or even improves kidney health over time.

Your overall health status matters for clinical trial eligibility. Researchers need to ensure you are healthy enough to participate and that you do not have other medical conditions that could interfere with the study results or put you at risk. This means you may undergo a general physical examination, blood counts, liver function tests, and screening for infections before enrollment.

Throughout a clinical trial, you will undergo regular diagnostic tests to monitor your progress. These typically include repeated urine collections to measure protein levels, blood tests to check kidney function and safety markers, blood pressure checks, and sometimes repeat kidney biopsies. The frequency and type of monitoring depend on the specific trial protocol and the treatment being studied.

Participating in a clinical trial means committing to more frequent medical appointments and testing than you might have in standard care. However, this intensive monitoring can provide valuable information about your disease and potentially give you early access to promising new treatments before they become widely available.

Prognosis and Survival Rate

Prognosis

The outlook for people with FSGS varies widely depending on several factors. The type of FSGS you have plays a major role in determining your prognosis. People with secondary FSGS, where the disease results from another condition such as obesity or a viral infection, often have a better outlook if the underlying cause can be controlled or treated. In contrast, primary FSGS, where no cause is identified, tends to be more aggressive and harder to treat.

Proteinuria levels are among the most important predictors of how FSGS will progress. Higher levels of protein in the urine generally indicate more severe kidney damage and a greater risk of progression to kidney failure. Reducing proteinuria through treatment is associated with better preservation of kidney function over time. In fact, proteinuria serves as both a measure of disease activity and a contributor to further kidney damage, creating a cycle where more protein loss leads to worse kidney function.

Genetic testing results can also inform prognosis. People with genetic forms of FSGS, particularly those with certain mutations in genes that affect kidney filtering cells, may have disease that progresses differently than primary FSGS. Some genetic variants, such as APOL1 risk variants, are associated with more rapid progression to end-stage kidney disease and treatment resistance. However, genetic forms of FSGS have a lower risk of recurring after kidney transplant compared to primary forms.

How well someone responds to initial treatment strongly affects their long-term outlook. Achieving complete remission, where proteinuria disappears or drops to very low levels, is the best outcome and is associated with long-term preservation of kidney function. Partial remission, where proteinuria decreases but does not disappear completely, also improves prognosis compared to no response at all. Unfortunately, many people with primary FSGS are resistant to initial steroid treatment or become dependent on steroids, requiring ongoing medication to keep the disease under control.

The rate at which kidney function declines varies among individuals with FSGS. Some people maintain stable kidney function for many years, while others progress rapidly to kidney failure. Blood pressure control, reduction of proteinuria, and management of other complications such as high cholesterol all influence how quickly the disease advances. Without effective treatment, FSGS can lead to end-stage kidney disease requiring dialysis or kidney transplant.

For those who require kidney transplant, the risk of FSGS recurrence in the transplanted kidney is a significant concern. Between 30% and 40% of people with primary FSGS experience recurrence after transplant, which can cause the new kidney to fail. This recurrence often happens quickly, sometimes within hours or days of transplantation. However, people with genetic or secondary forms of FSGS have a much lower risk of post-transplant recurrence.

Survival Rate

FSGS is a serious condition that can lead to kidney failure, but survival depends on multiple factors including the effectiveness of treatment, the development of complications, and access to kidney replacement therapy when needed. In children with FSGS, about 20% progress to kidney failure, while approximately 5% of adults with FSGS develop end-stage kidney disease. These figures reflect the overall population of people diagnosed with FSGS, including those with different types and varying responses to treatment.

The time from diagnosis to kidney failure varies considerably. Some people maintain adequate kidney function for many years with appropriate treatment and disease management. Others experience more rapid decline, particularly if they have high levels of proteinuria that do not respond to treatment or if they develop severe complications such as uncontrolled high blood pressure. The progressive nature of FSGS means that kidney function tends to decline over time even with treatment, though the rate of decline can often be slowed significantly.

Once kidney failure occurs, dialysis or kidney transplantation becomes necessary for survival. With modern dialysis techniques and transplant medicine, people with end-stage kidney disease from FSGS can live for many years. However, quality of life and long-term outcomes are better with successful kidney transplantation compared to long-term dialysis. The challenge of disease recurrence after transplant remains a major concern that affects long-term graft survival in some patients.

Focal segmental glomerulosclerosis Diagnostics

Clinical trials for Focal segmental glomerulosclerosis