Complement Deficiencies Workup

Updated: Mar 01, 2017
  • Author: Robert A Schwartz, MD, MPH; Chief Editor: Michael A Kaliner, MD  more...
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Workup

Laboratory Studies

One can screen for deficiencies in complement by performing the total serum classic hemolytic complement (CH50) test or the alternative hemolytic complement (AP50) test. The CH50 test specifically tests for deficiencies in the classic pathway by measuring the ability of the patient's serum to lyse antibody-coated sheep erythrocytes. A deficiency in any of the classic proteins results in a CH50 of zero. Similarly, the AP50 tests for alternative pathway activity. Direct measurement of individual serum complement proteins, such as C3 and C4, can also be performed and is helpful in determining the diagnosis.

Dried blood spot samples from newborns, which are already widely used in neonatal screening for selected metabolic diseases, may be employed in the future using reverse phase protein microarrays for determination of complement component C3 levels collected at birth. [16] In one recent study, normal levels of C3 were detected from healthy newborns, while no C3 was documented in sera and dried blood samples from patients who were C3 deficient in C3. [16]

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Imaging Studies

No specific imaging studies are indicated. Consider performing a head CT scan prior to a lumbar puncture in a patient thought to have meningitis.

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Other Tests

Patients with classic complement pathway deficiencies should be screened for sequelae of immune complex diseases. Urinalysis and a complete blood cell count should be performed on these patients.

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Procedures

A lumbar puncture should be performed on patients with possible meningitis to assist in the definitive diagnosis of bacterial meningitis.

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