Sample stability:
- 5 days at 20 - 25 o C
- 7 days at 2 - 8 o C
- 30 days at -20 o C
Units: pmol/L
|
>=4 days - 1 month |
10 - 40 |
|
>1 month - 1 year |
10 - 30 |
|
>1 year - 12 years |
11 - 22 |
|
>12 years - adult |
12 - 22 |
Pregnancy:
Gestational age (weeks)
FT4 (pmol/L)
<7 (as non-pregnant)
12 - 22
7
+0
- 13
+6
12 - 21
14
+0
- 28
+0
10 - 18
28
+1
- 40
+0
9 - 16
The reference interval is highly variable during the first three days of life.
Please contact a Paediatric Endocrinologist or Paediatrician if interpretation of these results is required.
Uncertainty of Measurement: 8%
Principle: Competitive type immunoassay with chemiluminescence detection
Reagents: Roche FT4 IV
Analyser: Cobas e801
The TSH test is the most sensitive marker of thyroid dysfunction. In most cases, TSH alone is all that is required to screen for thyroid disorders.
Temporary hypothalamic/pituitary dysfunction (aka 'sick euthyroid syndrome') may occur with acute illness and can create a confusing thyroid function pattern. Therefore, it is generally NOT recommended to assess thyroid function when a patient is acutely unwell, unless it is believe that thyroid dysfunction is the basis of the illness.
Drug and other interferences in free T4 and free T3 assays
Free T4 and Free T3 assays attempt to measure a very small fraction of free hormone against a much larger background of bound hormone. Consequently these assays are prone to give incorrect estimates of free hormone when the concentration or affinity of binding proteins (TBG and albumin) are abnormal, or when drugs displace the hormone from the binding proteins. These effects vary with the assay used.
The Roche free T4 and free T3 assays are in use at labplus. The manufacturer states that of 26 commonly used drugs , only furosemide caused elevated free T4 and low free T3 at therapeutic dosage.
References
Stockigt, J. R. and C. F. Lim (2009). "Medications that distort in vitro tests of thyroid function, with particular reference to estimates of serum free thyroxine." Best Pract Res Clin Endocrinol Metab 23(6): 753-767
Emails to chemicalpathologist@adhb.govt.nz will receive priority attention from the on-call chemical pathologist.
If the query concerns a specific patient please include the NHI number in your email.
If email is not a suitable option, please contact the on-call chemical pathologist via Lablink (Auckland City Hospital ext. 22000 or 09-3078995).
Individual chemical pathologists may be contacted but will not be available at all times.
After-hours : contact Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours.
Dr Samarina Musaad (Clinical Lead) : SamarinaM@adhb.govt.nz ext. 22402
Dr Cam Kyle: CampbellK@adhb.govt.nz ext 22052
Dr Weldon Chiu: WeldonC@adhb.govt.nz ext. 23427
Dr Campbell Heron: CHeron@adhb.govt.nz ext. 23427
Dr Sakunthala Jayasinghe: Sakunthala@adhb.govt.nz ext. 23427