Since autoimmune diseases can affect multiple organs and produce highly variable signs and symptoms that can change in severity over time, recognizing and diagnosing autoimmune diseases can be difficult. Signs and symptoms can be vague, slow to present, and cause incorrect diagnoses. In addition, laboratory tests used to diagnose autoimmune disorders often depend on the particular disorder suspected. Blood tests that indicate the presence of inflammation are usually performed to help diagnose an autoimmune disorder. When autoimmune disease is suspected, the common laboratory evaluation will serve as an initial red flag to pursue further testing. Initially, it is typical that one or more of the following laboratory tests may be performed:
Hematology
Characteristic findings on a complete blood count (CBC) can include normocytic, normochromic anemia indicating the chronicity or severity of a disease and an elevated or decreased platelet count and/or white blood cell count. Leukopenia and thrombocytopenia are common in patients with systemic lupus erythematosus (SLE). Some inflammatory conditions can lead to a slight microcytic, hypochromic anemia. Pernicious anemia, caused by an inability to absorb vitamin B12, is generally macrocytic.
Chemistry
Depending on the specific autoimmune disease, testing for serum levels of specific organ enzymes or abnormalities in metabolic processes may show an elevation of transaminases (ALT and AST), creatine kinase, bilirubin, and other serum proteins (immunoglobulins).
Coagulation
Coagulation studies may show elevations in the activated partial thromboplastin time (aPTT) and/or the prothrombin time (PT), which could suggest an inhibitor of the clotting process as seen in certain autoimmune disorders such as antiphospholipid syndrome.
Urinalysis
In autoimmune disorders, the urinalysis is commonly used to assess renal injury (glomerulonephritis, interstitial nephritis). It can show proteinuria, hematuria, or clinically significant microscopic elements (e.g., white blood cell casts, red blood cell casts, waxy casts, fatty casts).
