At a glance
| Analyte | Total thyroxine |
|---|---|
| Also called | Total T4, Thyroxine |
| Method | Competitive chemiluminescence immunoassay |
| Sample type | Serum, Plasma |
| Panel | Thyroid |
| Discipline | CLIA immunoassay |
| Brand | Mindray |
What T4 measures
Total thyroxine counts the hormone bound to carrier proteins together with the small free fraction, so it measures the whole circulating pool. It was the standard thyroid hormone measurement before free assays became routine, and it remains in use. Its limitation is well understood: because most thyroxine is protein-bound, the total moves whenever carrier protein concentrations move. Pregnancy, oestrogen therapy and certain inherited variations all shift carrier proteins and therefore shift the total T4 without any change in thyroid status. Read with TSH it still contributes useful information, and in a patient with normal carrier proteins it tracks the free measurement closely.
How Philippine laboratories run it
Total T4 continues to appear on Philippine request forms and in thyroid panel packages, often alongside total T3, because established ordering habits and older printed forms persist well after a laboratory has added the free assays to its menu. That is the practical reason to keep it on the menu rather than a clinical one, and it means laboratories frequently run both the total and free versions of the same hormone. Framar supplies all four so a laboratory can meet the requests it actually receives rather than the ones it would prefer to receive.
Analyzers it runs on
Calibrator, controls and companion tests
Delivered with the control material it is verified against and the rest of the thyroid panel, on the same schedule as T4.
Storage and handling
Refrigerated, upright, and not frozen.
Buying T4 in the Philippines
T4 is supplied for the CL-2600i and CL-900i. We deliver it with Thyroid Control and TSH, because a run held up waiting on a separate order costs the same shift a stock-out does. Delivery is scheduled against your monthly T4 count, so the bench is not rationing tests in the last week of the month. How we plan clia immunoassay supply.
Questions about T4
Should we still offer total T4 if we have FT4?
Many Philippine laboratories do, because requests still arrive written that way and printed forms outlast menu changes. Clinically the free measurement is the more robust one, since the total is affected by carrier protein levels that change in pregnancy and with oestrogen therapy. Keeping both on the menu is usually a decision about the requests you receive rather than about which test is better.
Order T4
Tell us your monthly T4 volume and we will quote a supply schedule for CL-2600i. We reply within one business day.
Request a quotation