What is the role of lab tests in the workup of complement deficiencies?

Updated: Apr 28, 2021
  • Author: Robert A Schwartz, MD, MPH; Chief Editor: Michael A Kaliner, MD  more...
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Answer

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. [21] 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. [21]


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