IgG Avidity by Enzyme Linked Immunosorbant Assay (ELISA)

Measurement of the avidity of rubella IgG antibodies to differentiate primary rubella infection from past exposure.

Serum or plasma (100 µL minimum) that has been determined to be rubella IgG positive.

Collect blood in serum separator tubes (SST) or EDTA tubes.

Follow standard laboratory techniques to prepare serum or plasma. Store at 4°C and ship at room temperature or on wet ice for arrival at the NML within 14 days of collection. Otherwise, freeze (-20°C or below) and ship frozen on dry ice.

Shipping of specimens shall be done by a TDG certified individual in accordance with TDG regulations. For additional information regarding classification of specimens for the purposes of shipping, consult either Part 2 Appendix 3 of the TDG Regulations or section 3.6.2 of the IATA Dangerous Goods Regulations as applicable.

1. Pregnant women with rubella IgM positive serology result or recent (within 30 days) contact with laboratory confirmed case of rubella. 2. Suspected cases of rubella that have had recent (within 30 days) contact with laboratory confirmed case of rubella. Patient samples must have been determined to be rubella IgG positive.

Completed Measles, Mumps, and Rubella requisition form. Include gestational week date of rash onset, date of fever onset, number of doses of rubella vaccine received, date of last rubella vaccination, travel history, and date of rubella exposure and/or MARS identifier (from the Measles and Rubella Surveillance application on CNPHI) or case number, as applicable. Also include Rubella IgM and IgG results.

An onset date and collection date must be indicated on the requisition for result interpretation. Please contact the lab in advance of sending samples for testing.

Testing is done using Euroimmun’s “avidity determination of IgG antibodies against rubella viruses” test kit (4). IgG avidity is the maturation of IgG subclasses from weak binding IgG antibodies to strong binding IgG antibodies over time after primary exposure to the antigen. Thus, low avidity IgG antibodies are indicative of an acute infection, while high avidity IgG antibodies are indicative of a past or re-infection. A commercial ELISA is used that compares results of a set of wells in the presence of a denaturant with the results of wells without the denaturant. Low avidity IgG antibodies will be washed off by the denaturant and are detected by a significant drop in the amount of IgG in the wells that have the denaturant as compared to the wells without. Using this assay, maturation from low to intermediate/high avidity occurs less than 30 days after exposure/infection to rubella virus. Therefore, for the interpretation of a high avidity result as a true past infection, and not a primary infection, the exposure date and serum collection date must not be more than 30 days apart. For questions regarding interpretation of rubella IgG avidity results please contact the lab at 204-789-7055.

7 calendar days. STAT testing is available upon request (contact the lab in advance).

1. Thomas H.I.J, P Morgan-Capner. Rubella Specific IgG1 avidity: a comparison of methods. J Viol. Meth. 1991; 31: 219-228.                     
2. Thomas, H.I.J, P Morgan-Capner, et al. Persistence of specific IgM and low avidity specific IgG1 following primary rubella. J Viol. Meth. 1992; 39: 149-155.
3. Hedman K, S.A. Rousseau. Measurement of Avidity of Specific IgG for Verification of Recent Primary Rubella. J Med. Viol. 1989; 27: 288-292.
4. Mubareka S, H Richards, M Gray, GA Tipples. Evaluation of commercial rubella immunoglobulin G avidity assays. J Clin Microbiol. 2007 Jan; 45(1):231-3.
5. Best JM, S O’Shea, G Tipples, N Davies, SM Al-Khusaiby, A Krause, LM Hesketh, L Jin, G Enders. Interpretation of rubella serology in pregnancy - pitfalls and problems. BMJ. 2002 Jul 20; 325 (7356): 147-8.
6. Robinson JL, BE Lee, JK Preiksaitis, S Plitt, GA Tipples. Prevention of congenital rubella syndrome - What makes sense in 2006? Epidemiologic Reviews. 2006;28:81-87.