what are C3 and C4 levels?

Question

exactly, when getting your blood taken.what is it measured for?

Answer 1

"PA-C" has the complex answer which may be difficult for you if you don't have a medical background.
The "C" or "Complement" cascade is a series of biochemical reactions that are part of our immune response system - more specifically dealing with inflammation. Sometimes the body is responding to an outside threat such as an infection, and sometimes the body attacks itself when the immune system is not functioning normally. C3 and C4 are elements of the inflammatory response. Measuring these add pieces to the diagnostic puzzle. It can tell us whether the immune system is activated, but it doesn't say what the precise cause may be. This is tricky stuff to explain simply.
MD - Internal Medicine

Answer 2

C3 and C4

Sample requirements: 5-10 ml clotted blood.

Raised levels of C3 and C4 levels are found in acute phase reactions and in chronic inflammation. Low C3 and C4 levels may occur in patients with SLE (systemic lupus erythematosus) particularly with renal involvement.

Low C3 levels are found in patients with membrane proliferative glomerulonephritis or partial lipodystrophy associated with the presence of C3 nephritic factor.

Low C3 levels, which return to normal in convalescence, are associated with acute post-streptococcal glomerulonephritis.

Low C4 levels occur in patients with angioedema or cryoglobulinaemia.

Single point determinations of C3 and C4 are of limited value and serial measurements are recommended.

Normal range C3: 0.7 - 1.7 g/L, C4: 0.13 - 0.43 g/L.