Test code: 158
The
complement system is an essential part of the immune system (1). It consists of
a set of more than 40 proteins that can be activated through 3 different
pathways. The complement system plays a key role in the elimination of
pathogens such as bacteria and viruses, as well as in promoting inflammatory
responses and other immune functions. Its proteins work together to identify
and eliminate foreign organisms or infected cells.
The
complement proteins that are most commonly determined in clinical practice are
C3 and C4. Total complement activity (also known as hemolytic complement
activity or CH50) is determined when there is suspicion of a deficiency that
cannot be defined using C3 and C4. CH50 measures the overall function of the
classical complement pathway, C1-C9.
In our
laboratory, CH50 activity is quantified using a liposome-based technique. The
reference intervals provided by the reagent manufacturer range from 31.6 to
57.6 U/mL. These values are based on studies conducted in a Japanese
population. However, geographical differences can influence the complement
system and, therefore, the reference values (2). To establish a more accurate
reference interval for our population, Synlab has conducted a study with an
anonymized sample of 17,084 individuals in whom CH50 determination was
performed in our reference laboratory.
The
biological reference interval estimation was carried out following the CLSI
EP28-A3C protocol using outlier exclusion and an indirect method based on
repeated sampling techniques (Bootstrap). The produced reference interval is
from 36.5 to 83.7 U/mL.
Additionally,
the unilateral 95% reference interval was estimated, which would be the most
appropriate for clinical use, given that pathological CH50 values are related
to its deficiency, while values above the upper limit are generally not
associated with pathology but with inflammatory processes. This unilateral
reference interval (95% CI) would be > 39.8 U/mL.
These newly
obtained values are consistent with the findings of a similar study on CH50
activity in a European population (3).
As a
result, starting from 24/03/2025, Synlab will adopt the unilateral
reference interval of > 39.8 U/mL as the discriminating value for the
study of CH50 activity alterations. This update will allow for better
interpretation of results and greater accuracy in the diagnosis of complement
system-related disorders in our population.
References
- Costabile M. Measuring the 50%
haemolytic complement (CH50) activity of serum. J Vis Exp. 2010 Mar
29;(37):1923. doi: 10.3791/1923. PMID: 20351687; PMCID: PMC3168207
- Delanghe JR, Speeckaert R,
Speeckaert MM. Complement C3 and its polymorphism: biological and clinical
consequences. Pathology 2014;46:1–10.
- Sara Capiau, Joris R. Delanghe
and Pieter M. De Kesel* Evaluation of reference intervals for classical
and alternative pathway functional complement assay.
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