Definition of reference limits for autoantibodies to thyroid peroxidase and thyroglobulin in a large population of outpatients using an indirect method based on current data.
BACKGROUND
The reference limits for thyroid antibodies are generally made by measuring thyroid peroxidase and thyroglobulin antibody values in a group of healthy subjects (direct method), as proposed by the National Academy of Clinical Biochemistry.


OBJECTIVE
To define the upper reference limits of thyroid peroxidase and thyroglobulin, by using an indirect method to analyze data from a large number of outpatients that were stored in the information system of a general hospital laboratory.


METHODS
Thyroid peroxidase and thyroglobulin values from 21 492 patients, who had undergone antithyroid antibody measurements, were retrieved from the laboratory information system; the upper reference limits (in the top 97.5 percentile) were calculated using the indirect Kairisto method, after exclusion of outliers.


RESULTS
The mean upper reference limits for females and males were 15 kIU/L and 9 kIU/L for thyroid peroxidase, and 21 kIU/L and 19 kIU/L for thyroglobulin, respectively. The upper limits showed minimal or no differences in the different age classes in either females or males.


CONCLUSIONS
Using a vast population of patients, we demonstrated that the upper limits for thyroid antibodies are much lower than the values obtained with classic, direct methods and that they do not vary in relation to age and sex.
Tozzoli
Renato
R
Laboratory of Clinical Pathology, Ospedale Civile, Latisana, Italy.
Giavarina
Davide
D
Villalta
Danilo
D
Soffiati
Giuliano
G
Bizzaro
Nicola
N
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001323:Autoantibodies / Q000097:blood*; D002648:Child; D005260:Female; D006801:Humans; D007453:Iodide Peroxidase / Q000276:immunology*; D007755:Laboratories, Hospital; D008297:Male; D008875:Middle Aged; D010045:Outpatients; D010338:Pathology, Clinical / Q000379:methods*; D012015:Reference Standards; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013954:Thyroglobulin / Q000276:immunology*; D013967:Thyroiditis, Autoimmune / Q000097:blood / Q000175:diagnosis / Q000276:immunology; D055815:Young Adult
D001323:Autoantibodies; D013954:Thyroglobulin; D007453:Iodide Peroxidase