Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (883 page)

   The sensitivity of CCP-IgG for RA varies from about 50–75%, depending on the assay and study population, whereas specificity for RA is relatively high, usually >90%.

   Not all individuals with RA will have detectable anti-CCP antibodies, and elevated anti-CCP antibodies may be seen in individuals with no evidence of clinical disease.

   The use of anti-CCP antibody levels for monitoring the progression and/or remission of RA has not been established.

   The diagnostic value of anti-CCP antibodies has not been determined for juvenile arthritis.

Suggested Reading

Aletaha D, Neogi T, Silman A, et al. 2010 Rheumatoid arthritis classification criteria: an American College of Rheumatology/European League Against Rheumatism collaborative initiative.
Ann Rheum Dis.
2010;69(9):1580–1588.

CYSTATIN C (CysC)

   Definition

   CysC is a 13-kDa, nonglycosylated basic protein that is produced by all nucleated cells. It is a cysteine protease inhibitor. Cystatin C is present in all investigated body fluids and is not affected by age, gender, muscle mass, or the inflammatory process. Cystatin C is removed from circulation by glomerular filtration and is completely reabsorbed and degraded in the tubules. Therefore, the plasma concentration of cystatin C is almost exclusively determined by the GFR, making cystatin C an excellent indicator of GFR.

   
Normal range:

   0–3 months: 0.8–2.3 mg/L

   4–11 months: 0.7–1.5 mg/L

   1–3 years: 0.5–1.3 mg/L

   4–8 years: 0.5–1.3 mg/L

   9–17 years: 0.5–1.3 mg/L

   ≥18 years: 0.5–1.0 mg/L