Lab tests to determine the etiology of acute glomerulonephritis
Aside from urinalysis, which other laboratory tests are useful in determining the etiology of acute glomerulonephritis?
Certain serologic studies or other laboratory tests may be useful in narrowing the differential diagnosis, but ordering these labs should be guided by the patient’s history and clinical presentation.
Complement levels (C3, C4) are usually normal in patients with either primary RPGN or RPGN associated with systemic diseases. Lupus is an exception, as these patients usually have depressed C3 and C4 levels.
In almost all patients, an antinuclear antibody level is a useful screen for lupus or other connective tissue diseases. Identification of anti-GBM antibodies and anti-neutrophil cytoplasmic antibodies (ANCA) can be useful in establishing a diagnosis in patients with RPGN. Patients who are ANCA antibody positive frequently have a primary small vessel vasculitis.
The patient’s clinical presentation determines the predictive value of ANCA testing. For example, the predictive value of a positive ANCA test is lower in a patient who presents with hematuria, proteinuria, and a normal creatinine than in a patient with similar urinalysis findings in the presence of azotemia.
Laboratory testing to identify infections with Streptococcus, hepatitis, or HIV, or causes of autoimmune diseases in addition to lupus and ANCA vasculitis, may be indicated.
Antibodies to phospholipase A2 receptor (PLA 2 R) are found in 70% of cases of idiopathic membranous nephropathy. Testing for anti-PLA 2 R antibodies is reasonable in selected patients with RPGN syndromes.