Patient description: The patient is a 23-year-old man who came to the hospital with high blood pressure (175/95 mmHg) and signs of septicemia. He developed respiratory failure requiring mechanical ventilation and renal failure requiring hemodialysis. His blood smear showed microangiopathic hemolytic anemia and thrombocytopenia. His blood tests revealed elevated lactate dehydrogenase and reduced human complement C3 levels with a normal coagulation profile. He was diagnosed with atypical hemolytic uremic syndrome. He was treated with plasma exchange and corticosteroids. He has been previously vaccinated with meningococcal group ACWY conjugate vaccine and meningococcal group B vaccine. The genetic survey revealed ADAMTS13 >10%.

Clinical trial eligibility criteria: eligible ages (years): 18.0-999.0,  Thrombotic Microangiopathy 18 years of age or older 2. Body weight ≥ 30 kilograms 3. Female participants of childbearing potential and male participants with female partners of childbearing potential must use highly effective contraception starting at screening and continuing until at least 8 months after the last dose of ravulizumab 4. Diagnosis of TMA associated with a trigger 5. Vaccinated against meningococcal infection (Neisseria meningitidis), within 3 years prior to, or at the time of, randomization. Participants who initiate study drug treatment less than 2 weeks after receiving a meningococcal vaccine must receive appropriate prophylactic antibiotics for at least 2 weeks after the vaccination. If participant cannot receive the meningococcal vaccine, then participant must be willing to receive antibiotic prophylaxis coverage against N. meningitidis during the entire Treatment Period and for 8 months following the final dose of study drug. Additional vaccination (Haemophilus influenzae type b (Hib) and Streptococcus pneumoniae) may be considered based on individual patient condition  Any known gene mutation that causes atypical hemolytic uremic syndrome (aHUS) 2. Postpartum aHUS 3. Known chronic kidney disease with estimated glomerular filtration rate ≤ 45 mL/min/1.73 m^2 due to any cause 4. TMA due to hematopoietic stem cell transplantation ≤ 12 months of Screening 5. Primary and secondary glomerular diseases other than lupus 6. Diagnosis of primary antiphospholipid antibody syndrome 7. Shiga toxin-producing Escherichia coli infections including but not limited to Shiga toxin-related hemolytic uremic syndrome 8. Known familial or acquired 'a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13' (ADAMTS13) deficiency (activity < 5%) 9. Positive direct Coombs test 10. Diagnosis of disseminated intravascular coagulation (DIC) 11. Presence of sepsis according within 7 days prior to or during Screening 12. Presence of monoclonal gammopathy including but not limited to multiple myeloma 13. Known bone marrow insufficiency or failure evidenced by cytopenias 14. Unresolved N. meningitidis infection 15. History of malignancy within 5 years of Screening with the exception of nonmelanoma skin cancer or carcinoma in situ of the cervix that has been treated with no evidence of recurrence 16. Use of any complement inhibitors within the past 3 years