Immunostaining showing IgA in the glomerulus of a patient with<unk><unk><unk>  nephritis The diagnosis is based on the combination of the symptoms, as very few other diseases cause the same symptoms together. Blood tests may show elevated creatinine and urea levels (in kidney involvement), raised IgA levels (in about 50%), and raised C-reactive protein (CRP) or erythrocyte sedimentation rate (ESR) results; none are specific for<unk> . The platelet count may be raised, and distinguishes it from diseases where low platelets are the cause of the<unk> , such as idiopathic thrombocytopenic<unk>  and thrombotic thrombocytopenic<unk> . If there is doubt about the cause of the skin lesions, a biopsy of the skin may be performed to distinguish the<unk>  from other diseases that cause it, such as vasculitis due to cryoglobulinemia; on microscopy, the appearances are of a hypersensitivity vasculitis, and immunofluorescence demonstrates IgA and C3 (a protein of the complement system) in the blood vessel wall. However, overall serum complement levels are normal. On the basis of symptoms, it is possible to distinguish<unk>  from hypersensitivity vasculitis (HV). In a series comparing 85<unk>  patients with 93 HV patients, five symptoms were found to be indicative of<unk> : palpable<unk> , abdominal angina, digestive tract hemorrhage (not due to intussussception), hematuria and age less than 20. The presence of three or more of these indicators has an 87% sensitivity for predicting<unk> . Biopsy of the kidney may be performed both to establish the diagnosis or to assess the severity of already suspected kidney disease. The main findings on kidney biopsy are increased cells and Ig deposition in the mesangium (part of the glomerulus, where blood is filtered), white blood cells, and the development of crescents. The changes are indistinguishable from those observed in IgA nephropathy. histological section of human skin prepared for direct immunofluorescence using an anti-IgA antibody, the skin is a biopsy of a patient with<unk> . IgA deposits are found in the walls of small superficial capillaries (yellow arrows). The pale wavy green area on top is the epidermis, the bottom fibrous area is the dermis.<unk>  can develop after infections with streptococci (β-haemolytic, Lancefield group A), hepatitis B, herpes simplex virus, parvovirus B19, Coxsackievirus, adenovirus, Helicobacter pylori, measles, mumps, rubella, Mycoplasma and numerous others. Drugs linked to<unk> , usually as an idiosyncratic reaction, include the antibiotics vancomycin and cefuroxime, ACE inhibitors enalapril and captopril, anti-inflammatory agent diclofenac, as well as ranitidine and streptokinase. Several diseases have been reported to be associated with<unk> , often without a causative link. Only in about 35% of cases can<unk>  be traced to any of these causes. The exact cause of<unk>  is unknown, but most of its features are due to the deposition of abnormal antibodies in the wall of blood vessels, leading to vasculitis. These antibodies are of the subclass IgA1 in polymers; it is uncertain whether the main cause is overproduction (in the digestive tract or the bone marrow) or decreased removal of abnormal IgA from the circulation. It is suspected that abnormalities in the IgA1 molecule may provide an explanation for its abnormal behaviour in both<unk>  and the related condition IgA nephropathy. One of the characteristics of IgA1 (and IgD) is the presence of an 18 amino acid-long "hinge region" between complement-fixating regions 1 and 2. Of the amino acids, half is proline, while the others are mainly serine and threonine. The majority of the serines and the threonines have elaborate sugar chains, connected through oxygen atoms (O-glycosylation). This process is thought to stabilise the IgA molecule and make it less prone to proteolysis. The first sugar is always N-acetyl-galactosamine (GalNAc), followed by other galactoses and sialic acid. In<unk>  and IgAN, these sugar chains appear to be deficient. The exact reason for these abnormalities is not known. Classification Multiple standards exist for defining<unk> , including the 1990 American College of Rheumatology (ACR) classification and the 1994 Chapel Hill Consensus Conference (CHCC). Some have reported the ACR criteria to be more sensitive than those of the CHCC. More recent classifications, the 2006 European League Against Rheumatism (EULAR) and Pediatric Rheumatology Society (PReS) classification, include palpable<unk>  as a mandatory criterion, together with at least one of the following findings: diffuse abdominal pain, predominant IgA deposition (confirmed on skin biopsy), acute arthritis in any joint, and renal involvement (as evidenced by the presence of blood and/or protein in the urine). Differential diagnosis<unk>  may present with an atypical manifestation, which can be confused with papular urticaria, systemic lupus erythematosus, meningococcemia, dermatitis herpetiformis, and acute hemorrhagic edema of infancy.
Henoch–Schönlein purpura
Chronic testicular pain
Amyloid purpura
Testicular pain
Golfer's vasculitis
Hennekam syndrome
Roussy–Lévy syndrome
Solar purpura