METABOLIC AND SCINTIGRAPHIC STUDIES OF RADIOIODINATED HUMAN C-REACTIVE PROTEIN IN HEALTH AND DISEASE

Plasma and whole-body turnover studies of human C-reactive protein (CR P), isolated from a single normal healthy donor and labeled with I-125 , Were undertaken in 8 healthy control subjects and 35 hospitalized pa tients including cases of rheumatoid arthritis, systemic lupus erythem atosus, infections, and neoplasia. Plasma clearance of I-125-CRP close ly approximated to a monoexponential function and was similar in the c ontrol and all patient groups. There was no evidence for accelerated c learance or catabolism of CRP in any of the diseases studied. The 19-h half-life was more rapid than that of most human plasma proteins stud ied previously, and the fractional catabolic rate was independent of t he plasma CRP concentration. The synthesis rate of CRP is thus the onl y significant determinant of its plasma level, confirming the validity of serum CRP measurement as an objective index of disease activity in disorders associated with an acute-phase response. Approximately 90% of injected radioactivity was recovered in the urine after 7 d, and sc intigraphic imaging studies with I-123-labeled CRP in 10 patients with different focal pathology showed no significant localization of trace r. The functions of CRP are thus likely to be effected predominantly i n the fluid phase rather than by major deposition at sites of tissue d amage or inflammation.