A 10-year-old boy is brought to the emergency department by his parents due to increasing lethargy and high fever for the past 12 hours. The boy was well last night but was sluggish this morning. Over the day, his activity level and responsiveness diminished. The patient was treated for Neisseria meningitidis bacteremia 2 years ago. He has received all routine vaccinations and is developing normally. Temperature is 39.6 C (103.3 F). On examination, the patient appears ill and is poorly responsive. He is tachycardic, but heart sounds are otherwise unremarkable. Lungs are clear to auscultation. Numerous purple bruise-like markings and petechiae are noted over his extremities, which have diminished capillary refill. Blood samples are drawn for total complement (CH50) and alternative complement (AH50) measurement. Which of the following sets of results is most likely to be found in this patient?

Question

A 10-year-old boy is brought to the emergency department by his parents due to increasing lethargy and high fever for the past 12 hours.  The boy was well last night but was sluggish this morning.  Over the day, his activity level and responsiveness diminished.  The patient was treated for Neisseria meningitidis bacteremia 2 years ago.  He has received all routine vaccinations and is developing normally.  Temperature is 39.6 C (103.3 F).  On examination, the patient appears ill and is poorly responsive.  He is tachycardic, but heart sounds are otherwise unremarkable.  Lungs are clear to auscultation.  Numerous purple bruise-like markings and petechiae are noted over his extremities, which have diminished capillary refill.  Blood samples are drawn for total complement (CH50) and alternative complement (AH50) measurement.  Which of the following sets of results is most likely to be found in this patient?

Quizplus · Accepted Answer

Eductional Objective: Initial control of encapsulated bacteria is largely reliant on the formation of membrane attack complexes (MACs) due to activation of the alternative complement cascade.  Patients with deficiency in the proteins that generate MACs (C5-9) are at high risk for recurrent encapsulated bacterial infection; evaluation will show reduced activity of the classical (CH50) and alternative (AH50) complement cascades.

A 10-Year-Old Boy Is Brought to the Emergency Department by His