Complement Disorders

Causes & Risk Factors

Complement abnormalities can result from either primary (inherited) or secondary (acquired) causes:

•  Primary (inherited) complement deficiency — genetic conditions affecting one or more complement components, which can increase susceptibility to certain infections, particularly encapsulated bacteria.

•  Secondary complement consumption — occurs when complement is used up faster than it is produced, commonly seen in active autoimmune disease (such as active lupus) or immune-complex disorders.

•  Certain infections can transiently affect complement levels.

•  Family history of recurrent, unusual, or severe infections (particularly meningococcal) may suggest an underlying complement deficiency.

Symptoms & When to Test

Complement disorders can present differently depending on whether the underlying cause is a primary deficiency or secondary consumption related to another condition.

•  Recurrent infections, particularly with encapsulated bacteria (such as Neisseria species) — suggestive of possible complement deficiency

•  Symptoms of an underlying autoimmune disease (such as SLE), where complement consumption may reflect disease activity

•  Recurrent angioedema (swelling episodes) — relevant to specific complement-related conditions such as hereditary angioedema

•  Family history of similar infection patterns or angioedema episodes

When Should You Consider Testing?

Testing is generally considered for recurrent infections with unusual organisms (particularly encapsulated bacteria), as part of monitoring known autoimmune disease activity, or when a specific complement-related condition such as hereditary angioedema is suspected.

Why Tests Are Combined

C3 and C4 measure the levels of two specific complement components, while CH50 evaluates the overall functional activity of the classical complement pathway — together, they can help distinguish between a deficiency of a specific component versus a broader functional problem in the pathway.

A normal C3 and C4 with an abnormal CH50 can suggest a deficiency in a different complement component not directly measured by C3/C4 alone, illustrating why functional (CH50) and component-specific (C3, C4) testing are complementary rather than redundant.

In patients with known autoimmune disease, low C3 and C4 together often reflect active disease and complement consumption (rather than an inherited deficiency), which is a different clinical scenario requiring different interpretation than primary complement deficiency in a patient with recurrent infections.

Tests Available at NPL

Most allergy and immunology blood tests do not require fasting. However, some tests ordered at the same time may have specific preparation requirements. Please follow the instructions provided by your doctor or NPL.

Home Sample Collection

NPL offers convenient home sample collection for Complement Disorders blood tests, so you don't need to visit a lab in person.

→ Book your test online, via the NPL app, or by calling +977 1 5970147 and select a convenient time slot for home sample collection.

→ A certified and experienced NPL phlebotomist visits your home at the scheduled time, following strict hygiene and safety protocols.

→ Your sample is transported under controlled, monitored conditions to NPL's NABL ACCREDITED UNDER ISO15189:2012laboratory for processing.

→ Your digital report is delivered securely to your phone or email, along with access to download and share it as needed.

When to See a Doctor

•  Recurrent infections, particularly with unusual organisms such as Neisseria species (meningococcal infection)

•  Known autoimmune disease requiring monitoring of complement levels as a marker of disease activity

•  Recurrent unexplained swelling episodes (angioedema)

•  Family history of similar infection patterns or complement-related conditions