The hemolytic transfusion reaction is a potentially severe adverse reaction to blood transfusion that may be divided into acute episodes, occurring during the first 24 hours after blood administration and delayed ones, that are often less serious. AB0 incompatibilities cause severe distress, whereas non-AB0 incompatibility leads to milder discomfort. Symptoms occasionally resolve by themselves, but advanced cases require immediate treatment.
Any individual that has a history of blood transfusion or pregnancy is a potential candidate for a hemolytic transfusion reaction after blood administration. Initial signs may be nonspecific. An acute episode presents with pulmonary findings such as wheezing tachypnea or dyspnea, cardiovascular abnormalities like tachycardia and hypotension, renal anomalies like anuria or a change of urine color to reddish due to hemoglobinuria and systemic symptoms, such as high fever, chills, headaches, flushing or paleness, loss of consciousness and anxiety   . The involvement of digestive system may cause jaundice, nausea, and vomiting. The patient may complain of a chest, back or abdominal pain. If disseminated intravascular coagulation sets in, a bleeding tendency is described later during the course of the disease.
A delayed hemolytic transfusion reaction is often less severe, consisting only of anemia signs and fever, the latter present one week after the incompatible blood transfusion. In other cases, the disease has no specific symptoms and is incidentally discovered during laboratory investigations . Severe complaints usually arise after hemolyzed blood administration.
The magnitude of the hemolytic reaction depends on the volume of incompatible blood that was administered. Even 1 ml of blood can cause a reaction, but complaints usually appear after 5 to 20 ml are administered. If the clinical status declines, the physician should investigate the presence of acute renal failure, disseminated intravascular coagulation, and shock.
The hemolytic transfusion reaction is accompanied by hemolysis, therefore the physician should order tests that highlight its presence . The first step is to retype patient and donor blood and inspect patient urine and blood. Pink, red, brown or yellow color of plasma suggests hemolysis and hemoglobinemia, while red urine after centrifugation signifies hemoglobinuria. The Coombs test must follow. The direct test will be found positive. If the polyspecific direct antiglobulin test is positive, monospecific tests and antibody elution tests should be performed in order to identify the antibody involved. The antiglobulin exam becomes positive several days after the transfusion in case a delayed hemolytic reaction is present, therefore a sample of the transfused blood must be kept in the laboratory for at least 10 days . The patient's hemoglobin value will diminish again 1 or 2 weeks after the transfusion of incompatible blood. At that time, increased reticulocyte levels and spherocytes may also be noticed.
Other examinations that prove hemolysis are the reduction of the plasma haptoglobin and hemopexin concentration, as well as an increase in the lactate dehydrogenase and bilirubin levels. Unfortunately, none of these markers are specific for hemolysis, but their combined presence is a strong indicator of the condition. Additional recommended tests include the prothrombin time, activated partial thromboplastin time, D- dimers, platelet count and fibrinogen levels, that help diagnose disseminated intravascular coagulation. The renal function must be closely monitored.
If no incompatibilities are demonstrated, but the patient has the complaints described above, the blood bag must be tested for hemolysis, since the administration of hemolyzed blood may induce these symptoms. Other hemolysis causes should also be searched for in case no explanation is found by conventional methods  .