Hypocomplementemia: Key Points and Mnemonics

You don’t need to memorize which glomerulonephritides are associate with low complement and which are not. Rather, ask yourself one question: does this patient have persistent, aggressive, endovascular, systemic infectious or inflammatory processes? If the answer is “yes,” then the disease is associate with low complement levels. If the answer is “no,” then complement level will be normal.

Glomerulonephritides associated with hypocomplementemia are:

• Postinfectious glomerulonephritis: this category includes infective endocarditis, poststreptococcal glomerulonephritis, ventriculoperitoneal shunt infections (“shunt nephritis”), and visceral abscesses. Poststreptococcal glomerulonephritis is most commonly seen in connection with pharyngitis or cellulitis (erysipelas) from Group A β-hemolytic streptococcus, also known Streptococcus pyogenes. Pyogenes means “pus generating” so it should be particularly easy to remember that this organism is closely associated with an aggressive inflammatory response, and therefore glomerulonephritis and hypocomplementemia.
• Membranoproliferative or cryoglobulinemic glomerulonephritis. These two go together because they are both strongly associated with infections, particularly Hepatitis C, and hematologic malignancies. You can remember that membranoproliferative glomerulonephritis goes with various proliferative diseases, including infections, and that Cryoglobulinemia goes with Hepatitis C.
• Lupus nephritis. This one is also easy to remember if you know that systemic lupus erythematosus causes Libman-Sacks endocarditis, because endocarditis (bacterial) is already on this list!

And finally:

• Hypocomplementemia in a patient with recurrent angioedema suggests C1 inhibitor deficiency or dysfunction.
• Terminal complement deficiency (↓ C5-C9) is associated with recurrent disseminated neisserial infections. Patients with recurrent invasive neisserial infections, such as Neisseria meningitidis meningitis, meningococcemia or gonococcemia, must be evaluated for terminal complement deficiency. The workup is important because patients with terminal complement deficiency need to be vaccinated against encapsulated organisms, namely Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae type b.
• Cholesterol emboli syndrome is sometimes seen in the setting of recent catheterization. Patients present with purple toes and livedo reticularis. Workup often shows hypocomplementemia (↓ C3/C4), renal failure, eosinophilia and eosinophiluria.

References

• The Washington Manual of Medical Therapeutics (2010)
• The Merck Manual for Health Care Professionals (accessed 5/25/2013)
• Sabatine, Marc S., MD, MPH. Pocket Medicine, 4e (2011, excellent on cholesterol emboli syndrome and cryoglobulinemia)