Why is complement measured?
The complement system is part of the innate immune system that destroys microbes and immune complexes. In autoimmune diseases, many immune complexes are formed that actively consume complement, and its level in the blood drops. A decrease in C3 is characteristic of systemic lupus erythematosus in the acute phase, acute post-streptococcal and membranoproliferative glomerulonephritis, and cryoglobulinemia. The indicator is used not only for diagnosis, but also for monitoring the activity of lupus: a drop in C3 often precedes a clinical exacerbation, and normalization confirms the effectiveness of treatment. There are also congenital deficiencies of complement components, manifested by recurrent bacterial infections.
Why preparation is so important
The laboratory result is a number, but the correct number can only be obtained if the rules are followed. Eating changes the levels of glucose, lipids and a number of enzymes significantly; physical activity the day before increases CK and AST; smoking affects hormones; time of day is critical for cortisol and testosterone.
Therefore, a “bad analysis” often turns out to be a consequence of impaired preparation, and not an illness, and leads to unnecessary examinations and prescriptions.
General rules for donating blood
- on an empty stomach 8–12 hours, you can drink water
- Eliminate alcohol and intense exercise per day
- no smoking in an hour
- donate blood before physiotherapy, x-rays and massage
- Take medications in advance by agreeing with your doctor
- for hormones in women, take into account the day of the cycle
How to read the result
Reference values depend on the method and equipment of the laboratory, so it is correct to compare results only within the same laboratory. A deviation of a few percent from the normal limit in itself rarely matters - the overall picture and dynamics are important. It is up to the physician to interpret the analysis: an isolated indicator without a clinical context is often misleading.