An audit of total and free thyroxine measurements in screening for hypo and hyperthyroidism in patients using chemiluminescence immunoassay |
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| Authors: | J J Fleming S Rajaratnam M S Seshadri A S Kanagasabapathy |
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| Institution: | (1) Departments of Clinical Biochemistry, Christian Medical College and Hospital, 632 004 Vellore, Tamil Nadu, South India;(2) Endocrinology, Christian Medical College and Hospital, 632 004 Vellore, Tamil Nadu, South India;(3) Present address: 205 SMR Krishna, Sikh Road, 500009 Secunderabad, Andhra Pradesh |
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| Abstract: | An audit of 2509 patient specimens analyzed for both total thyroxine (TT4) and free thyroxine (FT4) by the ACS-180 automated
chemiluminescence immunoassay analyzer revealed that there were 219 discrepancies (8.7% of the total). A discrepancy was defined
as one analyte within its reference range and the other outside. The discrepant results were divided into 4 groups: group
A: normal TT4, but decreased FT4, 101 patients (4.0%); group B: increased TT4, normal FT4, 78 patients (3.1%); group C: decreased
TT4, normal FT4, 34 patients (1.4%); and group D: normal TT4, increased FT4, 6 patients (0.2%). TSH measurements were available,
by a 3rd generation chemiluminescent assay, in 142 of these patients, and were consistent with the FT4 result in 72 patients, with
TT4 in 61 cases and with neither in 9 patients. The clinical diagnosis was investigated in a subgroup of 43 endocrine patients.
Thirteen of the 20 endocrine patients in group A were diagnosed as hypothyroid, with a measured serum TSH, in 11 of them,
of median 14.6, range 1.2 to 46.2 μlU/ml. Eleven of the 19 endocrine patients in group B were on thyroid replacement, with
a measured serum TSH, in 7 of them of <0.01 μlU/ml. The audit of current laboratory practice led to a suggestion to replace
the current thyroid function screening strategy of measuring both TT4 and FT4 by the combination of FT4 and TSH. The reasons
for the discrepancies and the alternative strategies for screening of thyroid function are discussed. |
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| Keywords: | Audit Total thyroxine Free thyroxine TSH Thyroid screening |
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