Some forms of glomerulonephritis are diagnosed clinically, based on findings on history and examination. Other tests may include:

- Urine examination

- Blood tests investigating the cause, including FBC, inflammatory markers and special tests including (ASLO, ANCA, Anti-GBM, Complement levels, Antinuclear antibodies

- Biopsy of the kidney

- Renal ultrasonography is useful for prognostic purposes in finding signs of chronic kidney disease, which however may be caused by many other diseases than glomerulonephritis.

The differential diagnosis of acute proliferative glomerulonephritisis is based on the following:

The following diagnostic methods can be used for acute proliferative glomerulonephritis:

- Kidney biopsy

- Complement profile

- Imaging studies

- Blood chemistry studies

Clinically, acute proliferative glomerulonephritis is diagnosed following a differential diagnosis between (and, ultimately, diagnosis of) staphylococcal and streptococcal impetigo. Serologically, diagnostic markers can be tested; specifically, the streptozyme test is used and measures multiple streptococcal antibodies: antistreptolysin, antihyaluronidase, antistreptokinase, antinicotinamide-adenine dinucleotidase, and anti-DNAse B antibodies.

RPGN can be classified into three types, based upon the immunofluorescence patterns:

Serum analysis often aids in the diagnosis of a specific underlying disease. The presence of anti-Glomerular basement membrane (GBM) antibodies suggests type I RPGN; antinuclear antibodies (ANA) may support a diagnosis of systemic lupus erythematosus and type II RPGN; and type III and idiopathic RPGN are frequently associated with anti-neutrophil cytoplasmic antibodies (ANCA)-positive serum.

Impaired renal functions in an individual with 3 months or less of the condition is an indication of RPGN. An ultrasonographic examination of the abdomen should also be done. Upon urine examination, urinary sediment (proteinuria) can indicate proliferative glomerulonephritis, many cases of rapidly progressive glomerulonephritis need a renal biopsy to make a diagnosis.

For an adult patient with isolated hematuria, tests such as ultrasound of the kidney and cystoscopy are usually done first to pinpoint the source of the bleeding. These tests would rule out kidney stones and bladder cancer, two other common urological causes of hematuria. In children and younger adults, the history and association with respiratory infection can raise the suspicion of IgA nephropathy. A kidney biopsy is necessary to confirm the diagnosis. The biopsy specimen shows proliferation of the mesangium, with IgA deposits on immunofluorescence and electron microscopy. However, patients with isolated microscopic hematuria (i.e. without associated proteinuria and with normal kidney function) are not usually biopsied since this is associated with an excellent prognosis. A urinalysis will show red blood cells, usually as red cell urinary casts. Proteinuria, usually less than 2 grams per day, also may be present. Other renal causes of isolated hematuria include thin basement membrane disease and Alport syndrome, the latter being a hereditary disease associated with hearing impairment and eye problems.

Other blood tests done to aid in the diagnosis include CRP or ESR, complement levels, ANA, and LDH. Protein electrophoresis and immunoglobulin levels can show increased IgA in 50% of all patients.

The diagnosis of lupus nephritis depends on blood tests, urinalysis, X-rays, ultrasound scans of the kidneys, and a kidney biopsy. On urinalysis, a nephritic picture is found and red blood cell casts, red blood cells and proteinuria is found. The World Health Organization has divided lupus nephritis into five stages based on the biopsy. This classification was defined in 1982 and revised in 1995.

- Class I is minimal mesangial glomerulonephritis which is histologically normal on light microscopy but with mesangial deposits on electron microscopy. It constitutes about 5% of cases of lupus nephritis. Kidney failure is very rare in this form.

- Class II is based on a finding of mesangial proliferative lupus nephritis. This form typically responds completely to treatment with corticosteroids. It constitutes about 20% of cases. Kidney failure is rare in this form.

- Class III is focal proliferative nephritis and often successfully responds to treatment with high doses of corticosteroids. It constitutes about 25% of cases. Kidney failure is uncommon in this form.

- Class IV is diffuse proliferative nephritis. This form is mainly treated with corticosteroids and immunosuppressant drugs. It constitutes about 40% of cases. Kidney failure is common in this form.

- Class V is membranous nephritis and is characterized by extreme edema and protein loss. It constitutes about 10% of cases. Kidney failure is uncommon in this form.

About a third of untreated patients have spontaneous remission, another third progress to require dialysis and the last third continue to have proteinuria, without progression of renal failure.

Treatment of secondary membranous nephropathy is guided by the treatment of the original disease. For treatment of idiopathic membranous nephropathy, the treatment options include immunosuppressive drugs and non-specific anti-proteinuric measures. Recommended first line therapy often includes: cyclophosphamide alternating with a corticosteroid.

Drug regimens prescribed for lupus nephritis include mycophenolate mofetil (MMF), intravenous cyclophosphamide with corticosteroids, and the immune suppressant azathioprine with corticosteroids. MMF and cyclophosphamide with corticosteroids are equally effective in achieving remission of the disease. MMF is safer than cyclophosphamide with corticosteroids, with less chance of causing ovarian failure, immune problems or hair loss. It also works better than azathioprine with corticosteroids for maintenance therapy. Individuals with lupus nephritis have a high risk for B-cell lymphoma (which begins in the immune system cells).

Male gender, proteinuria (especially > 2 g/day), hypertension, smoking, hyperlipidemia, older age, familial disease and elevated creatinine concentrations are markers of a poor outcome. Frank hematuria has shown discordant results with most studies showing a better prognosis, perhaps related to the early diagnosis, except for one group which reported a poorer prognosis. Proteinuria and hypertension are the most powerful prognostic factors in this group.

There are certain other features on kidney biopsy such as interstitial scarring which are associated with a poor prognosis. ACE gene polymorphism has been recently shown to have an impact with the DD genotype associated more commonly with progression to kidney failure.

The GBM is rebuilt on top of the deposits, causing a "tram tracking" appearance under the microscope. Mesangial cellularity is increased.

The diagnosis can be confirmed on a blood sample using a genetic test.

It is possible to analyze urine samples in determining albumin, hemoglobin and myoglobin with an optimized MEKC method.

Rapidly progressive glomerulonephritis, also known as "crescentic GN", is characterised by a rapid, progressive deterioration in kidney function. People with rapidly progressive glomerulonephritis may present with a nephritic syndrome. In management, steroid therapy is sometimes used, although the prognosis remains poor. Three main subtypes are recognised:

- Type 1 is Goodpasture syndrome, an autoimmune disease also affecting the lung. In Goodpasture syndrome, IgG antibodies directed against the glomerular basement membrane trigger an inflammatory reaction, causing a nephritic syndrome and the coughing up of blood. High dose immunosuppression is required (intravenous methylprednisolone) and cyclophosphamide, plus plasmapheresis. Immunohistochemistry staining of tissue specimens shows linear IgG deposits.

- Type 2 is characterised by immune-complex-mediated damage, and may be associated with systemic lupus erythematosus, post-infective glomerulonephritis, IgA nephropathy, and IgA vasculitis.

- Type 3 rapidly progressive glomerulonephritis, also called "pauciimmune type", is associated with causes of vascular inflammation including granulomatosis with polyangiitis (GPA) and microscopic polyangiitis. No immune deposits can be seen on staining, however blood tests may be positive for the ANCA antibody.

Histopathologically, the majority of glomeruli present "crescents". Formation of crescents is initiated by passage of fibrin into the Bowman space as a result of increased permeability of glomerular basement membrane. Fibrin stimulates the proliferation of endothelial cells of Bowman capsule, and an influx of monocytes. Rapid growing and fibrosis of crescents compresses the capillary loops and decreases the Bowman space, which leads to kidney failure within weeks or months.

Type III is very rare, it is characterized by a mixture of subepithelial deposits and the typical pathological findings of Type I disease.

A candidate gene has been identified on chromosome 1.

Complement component 3 is seen under immunofluorescence.

It is characterized by glomerular basement membrane thickening (referred to as "tram-tracking of the basement membrane"), increased mesangial matrix and segmental and global glomerulosclerosis.

The differential diagnosis of tram-tracking includes membranoproliferative glomerulonephritis (especially hepatitis C), and thrombotic microangiopathies.

Along with obtaining a complete medical history, a series of biochemical tests are required in order to arrive at an accurate diagnosis that verifies the presence of the illness. In addition, imaging of the kidneys (for structure and presence of two kidneys) is sometimes carried out, and/or a biopsy of the kidneys. The first test will be a urinalysis to test for high levels of proteins, as a healthy subject excretes an insignificant amount of protein in their urine. The test will involve a 24-hour bedside urinary total protein estimation. The urine sample is tested for proteinuria (>3.5 g per 1.73 m per 24 hours). It is also examined for urinary casts, which are more a feature of active nephritis. Next a blood screen, comprehensive metabolic panel (CMP) will look for hypoalbuminemia: albumin levels of ≤2.5 g/dL (normal=3.5-5 g/dL). Then a Creatinine Clearance C test will evaluate renal function particularly the glomerular filtration capacity. Creatinine formation is a result of the breakdown of muscular tissue, it is transported in the blood and eliminated in urine. Measuring the concentration of organic compounds in both liquids evaluates the capacity of the glomeruli to filter blood. Electrolytes and urea levels may also be analysed at the same time as creatinine (EUC test) in order to evaluate renal function.

A lipid profile will also be carried out as high levels of cholesterol (hypercholesterolemia), specifically elevated LDL, usually with concomitantly elevated VLDL, is indicative of nephrotic syndrome.

A kidney biopsy may also be used as a more specific and invasive test method. A study of a sample’s anatomical pathology may then allow the identification of the type of glomerulonephritis involved. However, this procedure is usually reserved for adults as the majority of children suffer from minimum change disease that has a remission rate of 95% with corticosteroids. A biopsy is usually only indicated for children that are "corticosteroid resistant" as the majority suffer from focal and segmental glomeruloesclerosis.

Further investigations are indicated if the cause is not clear including analysis of auto-immune markers (ANA, ASOT, C3, cryoglobulins, serum electrophoresis), or ultrasound of the whole abdomen.

Over time, kidney failure can develop and most men with the disease will eventually require dialysis or kidney transplantation. For reasons which are not understood, women with the disease, although they often have blood in their urine, only rarely develop kidney failure. The disease has been shown to recur following kidney transplantation, however in most cases the kidney transplant has a normal lifespan.

Laboratory tests may reveal an increased sedimentation rate, elevated CRP, anemia and elevated creatinine due to kidney impairment. An important diagnostic test is the presence of perinuclear antineutrophil cytoplasmic antibodies (p-ANCA) with myeloperoxidase specificity (a constituent of neutrophil granules), and protein and red blood cells in the urine.

In patients with neuropathy, electromyography may reveal a sensorimotor peripheral neuropathy.

In people with microscopic hematuria, it is important to rule out any possible confounders such as menstruation in women, possible presence of semen in sample or recent rigorous exercise. In menstruating women, tests should be repeated during non-bleeding parts of their cycles. In individuals with history of recent rigorous exercise, urinalysis should be repeated 4–6 weeks following cessation of exercise. All women of child-bearing age should undergo a pregnancy test, and if positive should receive an ultrasound of their kidneys and bladder with further invasive diagnostic work-up deferred until completion of pregnancy.

If diagnostic work-up has been unyielding so far or the aforementioned risk factors are present, it is important to begin a thorough work-up for possible malignancy especially of the bladder and kidney by referring to a Urologist to look at the urethra and bladder with a cystoscopy and also performing additional imaging using CT urography, which provides a thorough view of the complete urinary system.

For individuals with persistent hematuria with no immediate identifiable cause, urinalysis should be repeated once a year, and if it is negative for 2 years then you can stop repeating the tests. However, if it is positive for 3 years, repeat anatomic evaluation should be done.

In children and some adults, FSGS presents as a nephrotic syndrome, which is characterized by edema (associated with weight gain), hypoalbuminemia (low serum albumin, a protein in the blood), hyperlipidemia and hypertension (high blood pressure). In adults, it may also present as kidney failure and proteinuria, without a full-blown nephrotic syndrome.

A broad classification of nephrotic syndrome based on underlying cause:

Nephrotic syndrome is often classified histologically:

Transplant glomerulopathy, abbreviated TG, is a disease of the glomeruli in transplanted kidneys. It is a type of renal injury often associated with chronic antibody-mediated rejection. However, transplant glomerulopathy is not specific for chronic antibody-mediated rejection; it may be the result of a number of disease processes affecting the glomerular endothelium.

For people with visible hematuria and evidence of blood clots, further imaging with an abdominal CT scan should be done and an urgent referral to a urologist made. Otherwise, the next step involves determining if source of bleeding is glomerular in nature as evidenced by presence of inappropriately shaped/dysmorphic red blood cells, presence of protein in the urine, new or worsening hypertension or swelling. If source is glomerular patients should be referred to a nephrologist for further evaluation. Non-glomerular source of bleeding will usually require further work-up by a urologist.