I was looking back over my son's immune testing results from last year. My son has daily pain issues but his C4 serum level was at 20 and normal range is (15-59). I went on the MAYO Clinic to see what this test checks for and I learned that it assess disease activity in lupus, glomerulonephritis, rheumatoid arthritis and autoimmune hemolytic anemia. I know he is in a normal range but it is in the low range. I'm wondering if I should request this test to be reran. Are there other test that could shed some more light or should I just let this go? I really want to understand why my son is in daily pain.