Abstract
The biological variation of anti‐TPO and anti‐Tg autoantibodies was studied in 17 clinically and biochemically stable female patients with autoimmune thyroid disease (AITD), at regular monthly intervals over a period of 6 consecutive months. The mean and standard deviation (SD), within‐subject coefficient of variation (CV), between‐subject CV, index of individuality, reliability coefficient, and critical differences were as follows: for anti‐TPO 238 (197) U/ml, 9.2%, 81.4%, 0.11, 0.96, and 27.6%; and for anti‐Tg 1,785 (3,170) U/ml, 6.9%, 174%, 0.04, 0.99, and 22.3%. The data indicate a low within‐subject CV, and a high between‐subject CV that is particularly pronounced for anti‐Tg. The high individuality of both autoantibodies indicates that an isolated result compared to conventional population‐based reference intervals is of very little value for diagnosis. Furthermore, the near to 1 reliability coefficient for both autoantibodies correctly classifies the patient with respect to his or her homeostatic mean antibody concentration in a 6‐month period of clinical and biochemical stability of thyroid disease. Imprecision goals for anti‐TPO and anti‐Tg antibodies are attainable with current methodology. J. Clin. Lab. Anal. 16:37–39, 2002. © 2002 Wiley‐Liss, Inc.
Keywords: anti‐Tg antibodies, anti‐TPO antibodies, autoimmune thyroid disease, biological variability
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