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TSH reflex FT4
Test CodeLAB5210099
CPT Codes
84443
Preferred Specimen
Gold top (serum separator tube)
Minimum Volume
Whole blood: 2 ml (4 full red-top microtainers)
Serum: 900 uL
Serum: 900 uL
Other Acceptable Specimens
Red Top tube acceptable
For babies - collect 3 red microtainers
For babies - collect 3 red microtainers
Instructions
If TSH is abnormal, testing will reflex to FT4
Note: Lithium Heparin plasma unacceptable (light green top tube)
Note: Lithium Heparin plasma unacceptable (light green top tube)
Specimen Stability
Serum samples may be stored for up to 7 days at 2–8 °C (36–46 °F) or 4 weeks at -20 °C (-4 °F).
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Do not use turbid specimens. Turbidity in specimens may affect test results.
Plasma is unacceptable for FT4.
Plasma is unacceptable for FT4.
Methodology
Immunometric
FDA Status
Approved
Setup Schedule
Everyday
Report Available
Same Day
Limitations
TSH Limitations:
Biotin levels in serum remain elevated for up to 24 hours after oral or intravenous biotin administration.
Heterophilic antibodies in serum or plasma samples may cause interference in immunoassays.These
antibodies may be present in blood samples from individuals regularly exposed to animals or who have been
treated with animal serum products. Results which are inconsistent with clinical observations indicate the
need for additional testing.
Thyroid hormone autoantibodies in samples may cause interference with this test. Results which are
inconsistent with clinical observations indicate the need for additional testing.
The performance of this test has not been established using neonatal specimens.
FT4 Limitations:
Substances that bind to the thyroid hormone binding proteins are known to cause an increase in the
apparent free thyroid hormone concentration. In those cases, the change in FT4 concentration represents
the actual increases in free hormone and should not be considered an interference of the test.
Thyroid hormone autoantibodies in serum samples may cause interference in free-hormone
immunoassays. Results which are inconsistent with clinical observations indicate the need for additional
testing.
Biotin levels in serum remain elevated for up to 24 hours after oral or intravenous biotin administration.
Heterophilic antibodies in serum or plasma samples may cause interference in immunoassays.These
antibodies may be present in blood samples from individuals regularly exposed to animals or who have been
treated with animal serum products. Results which are inconsistent with clinical observations indicate the
need for additional testing.
Thyroid hormone autoantibodies in samples may cause interference with this test. Results which are
inconsistent with clinical observations indicate the need for additional testing.
The performance of this test has not been established using neonatal specimens.
FT4 Limitations:
Substances that bind to the thyroid hormone binding proteins are known to cause an increase in the
apparent free thyroid hormone concentration. In those cases, the change in FT4 concentration represents
the actual increases in free hormone and should not be considered an interference of the test.
Thyroid hormone autoantibodies in serum samples may cause interference in free-hormone
immunoassays. Results which are inconsistent with clinical observations indicate the need for additional
testing.
Reference Range
TSH (<1 year old): No Reference Range Established
TSH: 0.47-4.68 uIU/mL
FT4: 0.78 - 2.19 ng/dL
TSH: 0.47-4.68 uIU/mL
FT4: 0.78 - 2.19 ng/dL
Performing Laboratory
HHN Laboratory
HHI Laboratory
