This test may exhibit interference when sample is collected from a person who is consuming a supplement with a high dose of biotin (also termed as vitamin B7 or B8, vitamin H, or coenzyme R). It is recommended to ask all patients who may be indicated for this test about biotin supplementation. Patients should be cautioned to stop biotin consumption at least 72 hours prior to the collection of a sample.
1 - 2 days
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
For more information, please view the literature below.
Thyroid Testing: Assessing Thyroid Disease in Your Patients
Serum (preferred) or plasma
1 mL
0.7 mL (Note: This volume does not allow for repeat testing.)
Red-top tube, gel-barrier tube, or green-top (lithium heparin) tube. Do not use oxalate, EDTA, or citrate plasma.
If a red-top tube or plasma is used, transfer separated serum or plasma to a plastic transport tube.
Room temperature
Temperature
Period
14 days
Refrigerated
Frozen
Freeze/thaw cycles
Stable x3
Citrate plasma specimen; improper labeling
Evaluate thyroid function and assess abnormal binding protein disorders
Circulating antibodies to thyroid hormones have also been reported to interfere with free hormone immunoassays.
Electrochemiluminescence immunoassay (ECLIA)
See table.1
Age
Range (pg/mL)
0 to 3 d
2.0-7.9
4 to 30 d
2.0-5.2
31 d to 12 m
1.6-6.4
13 m to 5 y
2.0-6.0
6 to 10 y
2.7-5.2
11 to 19 y
2.3-5.0
>19 y
2.0-4.4
Triiodothyronine (T3) normally represents only approximately 5% of the thyroid hormone and like thyroxine is almost entirely bound to the carrier proteins, with only 0.25% of the total being in the free state. Measurement of free triiodothyronine is of value in confirming the diagnosis of hyperthyroidism, when an elevated free or total thyroxine level is found. Abnormal total and free triiodothyronine concentrations may appear in T3 toxicosis, in the presence of normal thyroxine levels. Free T3 levels are unaffected by carrier protein variation.
