Download Thyroid Stimulating Immunoglobulin

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Thyroid Stimulating
Immunoglobulin: Graves’
Disease Hyperthyroidism
David Corwin, M.D. and Joel Adams, MLS (ASCP)CM
CLINICAL BACKGROUND
In Graves’ disease (GD), thyroid stimulating immunoglobulins (TSI) bind to the
TSH receptor (TSHR) and mimic TSH stimulation of the thyroid gland. Because TSI
induced thyroid hormone secretion is not controlled by negative feedback, this
stimulation leads to GD hyperthyroidism. The Thyroid Stimulating Hormone (TSH)
receptor contains a large extracellular domain that presents epitopes for a variety
of autoantibodies, including Thyroid Stimulating Immunoglobulins (TSI) and Thyroid
Blocking Immunoglobulins (TBI). In contrast to TSI, TBI bind to the TSH receptor
and inhibit TSH stimulation of thyroid cells, leading to hypothyroidism. TSHR
autoantibody (TRAb) assays cannot distinguish between TSI and TBI. The new
automated TSI assay utilizes recombinant human TSH receptors (hTSHR) for a more
specific detection of thyroid stimulating autoantibodies, which are the hallmark of
Graves’ disease. Unlike the previous cell culture method which indirectly measures
TSI by the presence of a reporter molecule, the new Immunochemiluminometric
Assay (ICMA) method directly measures the amount of thyroid stimulating
autoantibody.
CLINICAL APPLICATION
¡Testing for Thyroid Stimulating Immunoglobulin (TSIAB); along with Thyroid
Peroxidase (TPO) antibodies, and TSHR autoantibody (TSHRAB) helps determine
the cause of thyrotoxicosis, leading to fast and accurate patient diagnosis.
¡Detecting TSI in the blood is a specific diagnostic tool for the differential
diagnosis of Graves’ disease (GD).
¡The new ICMA method is a more objective, semi-quantitative measurement
ORDER CODE:
TSIAB
Quick Facts
¡Test code [TSIAB] replaces
test code [TSIA]
¡The new automated ICMA
assay is more clinically
sensitive (98.3%) and
specific (99.7%) than the
previous bioassay
¡This new automated, ICMA
TSI assay, is the only one of
its kind on the market.
¡TRAb assays cannot
distinguish between
stimulating and blocking
antibodies. This new TSI
assay specifically detects
only thyroid stimulating
antibodies, the hallmark of
Graves’ disease.
of the amount of TSI autoantibody, compared to the change in percent of basal
activity measured in the previous bioassay method.
¡Improved turnaround time is
now 1-4 days.
¡TSI measurements can be used for monitoring the response to GD therapy and
¡Early detection of
autoimmune thyroid disease
limits unnecessary laboratory
testing.
predicting remission or relapse, confirming Graves’ ophthalmopaty, and
predicting neonatal thyroid hyperthyroidism.1,2
¡Incorporating the TSI assay into existing diagnostic algorithms has been shown
to reduce overall direct costs of GD diagnosis by up to 43%, with the net cost of
avoiding misdiagnosis reduced by up to 85%.3
RESULTS INTERPRETATION
Results of > 0.10 IU/L indicate detection of thyroid stimulating autoantibodies and
should be used in conjunction with other clinical and laboratory findings to aid in
the diagnosis of patients suspected of having Graves’ disease (GD).
SELECTED REFERENCES
1.Gupta, Manjula K. Thyrotropin-receptor antibodies in thyroid diseases: advances in detection
techniques and clinical applications. Clinica Chimica Acta. 2000;293:1-29
2.M.R. Bjorgaas, H. Farstad, S.C. Christiansen, H-G.K. Blaas. Impact of thyrotrophin receptor
antibody levels on fetal development in two successive pregnancies in a woman with Graves’
disease. Horm, res. Paediatr. 79:39-43, 2012.
3.McKee A., Peyerl, F. TSI assay utilization: impact on costs of Graves’ hyperthyroidism diagnosis.
AJMC. 2012; 18(1):1-15.
www.paml.com
¡The new ICMA method can
use Serum (plain or
separator tubes), Li-Heparin,
or K2-EDTA.
Thyroid Stimulating Immunoglobulin:
Graves’ Disease Hyperthyroidism
METHODOLOGY
The new method is the only automated ICMA TSI assay of its kind on the market. It is intended to be used as a semiquantitative determination of thyroid stimulating autoantibodies specific to TSH receptors in human serum (including serumseparator tubes) or plasma (K2-EDTA or lithium heparin). The measurement of thyroid stimulating autoantibodies, in conjunction
with other clinical and laboratory findings, is used as an aid in the diagnosis of patients suspected of having Graves’ disease.
Limitations:
§ Short drawn K2-EDTA plasma samples may result in under-recovery of TSI results.
Enhancements:
§ Sample volume has been reduced to 0.5mLs.
§ Improved turnaround time.
§ Greater sensitivity and specificity of ICMA over the previous bioassay method.
TEST INFORMATION
THYROID STIMULATING IMMUNOGLOBULIN
DESCRIPTION
Thyroid Stimulating Immunoglobulin (TSI)
METHOD Immunochemiluminometric Assay (ICMA)
ORDER CODES TSIAB
CPT CODES 84445
SPECIMEN Preferred Specimen: Serum
REQUIREMENTS Alternate Specimen: Lithium-Heparin or K2-EDTA
Preferred Volume: 1.0 mL
Minimum Volume: 0.5 mL
Store and Transport: Refrigerated
UNACCEPTABLE Hemolysis; room temperature specimens; short drawn K2-EDTA tubes
CONDITIONS
SCHEDULE Monday - Saturday
TURNAROUND 1 - 4 days
TEST INFORMATION FOR THYROID DISEASE
If you have further questions, please refer to our Thyroid Testing Algorithm under the Disease Algorithms tab on PAML.com.
For more information, please contact your local sales representative.