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The glomerulus is a histologically complex structure consisting of the epithelial cells (podocytes), basement membrane, capillary endothelium, and mesangium. A variety of different insults can occur within these structures causing different patterns of injury. Examples of injuries that can affect any or all of the constituents of the glomerulus are (1) overwork injury, as in CKD or obesity; (2) an inflammatory process, such as SLE; (3) a podocyte protein mutation, as in hereditary focal segmental glomerulosclerosis (FSGS); or (4) a deposition disease, as in diabetes or amyloidosis. Different glomerular patterns of injury tend to cause different clinical syndromes or findings, which may help narrow the differential diagnosis; however, when a glomerular disease is suspected, a kidney biopsy may be needed to confirm the diagnosis.
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Glomerular diseases are clinically classified as either nephritic or nephrotic (Figure 24–4); these are distinguished by the presence (nephritic) or absence (nephrotic) of significant glomerular hematuria. Differentiation is important because it helps narrow the differential diagnosis of the underlying glomerular disease and guide further serologic evaluation prior to possible kidney biopsy (Tables 24–8 and 24–9).
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