Comparison of insulin autoantibody: polyethylene glycol and micro-IAA 1-day and 7-day assays.
BACKGROUND
Older studies of diabetes development typically utilized a 7-day incubation polyethylene glycol competitive insulin autoantibody assay (CIAA). Our standard micro-IAA assay (mIAA) utilizes precipitation with proteins A/G and 1-day incubation (1-day mIAA), but is less sensitive compared to the CIAA assay.


METHODS
We performed CIAA and mIAA assays in various conditions. We analyzed serum samples from 446 type 1 diabetes patients, from another set of 247 type 1 diabetes patients within 2 weeks of initiation of insulin treatment, from 150 healthy control donors, from 22 healthy participants in the diabetes autoimmunity study in the young (DAISY), and also coded sera from 50 patients with newly diagnosed type 1 diabetes and 50 blood donor control samples.


RESULTS
In the process of our study, we found that the key condition was the incubation time. Therefore, we extended the incubation time to 7 days (7-day mIAA assay). No CIAA-negative control was positive with either 1-day or 7-day mIAA. In a new onset type 1 diabetes and at risk cohorts (DAISY study), the 7-day mIAA identified an additional 18% as being positive along with 16% of those who were initially 1-day mIAA negative and CIAA positive. Most subjects detectable only with the 7-day mIAA assay had intermediate levels of CIAA (80-300 nU/mL) (p = 0.01).


CONCLUSIONS
The 7-day mIAA assay identifies a small but significant additional subset of individuals positive on the CIAA assay, while preserving specificity.
Babaya
Naru
N
Barbara Davis Center for Childhood Diabetes, University of Colorado, Aurora, CO 80045-6511, USA.
Yu
Liping
L
Miao
Dongmei
D
Wang
Jian
J
Rewers
Marian
M
Nakayama
Maki
M
Liu
Edwin
E
Barker
Jennifer M
JM
Eisenbarth
George S
GS
D001323:Autoantibodies / Q000097:blood*; D003922:Diabetes Mellitus, Type 1 / Q000097:blood; D006801:Humans; D007330:Insulin Antibodies / Q000097:blood*; D008832:Microchemistry / Q000379:methods; D015166:Monitoring, Immunologic / Q000379:methods*; D011092:Polyethylene Glycols; D011236:Prediabetic State / Q000097:blood; D015531:Radioimmunoprecipitation Assay / Q000379:methods; D012680:Sensitivity and Specificity; D013205:Staphylococcal Protein A; D013997:Time Factors
D001323:Autoantibodies; D007330:Insulin Antibodies; D013205:Staphylococcal Protein A; D011092:Polyethylene Glycols