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CPT 84439: Free Thyroxine (Free T4) Assay
CPT code 84439 identifies a laboratory test for free thyroxine (free T4), a key measure in thyroid function assessment used to diagnose and manage hypo- and hyperthyroid conditions. Free T4 testing is widely performed across outpatient and hospital laboratory settings and informs clinical decisions about thyroid hormone status and therapy. Nationally, this assay is a routine component of endocrine and primary care workups and influences medication management, monitoring of thyroid disease, and evaluation of abnormal thyroid function studies.
Key payers addressed include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find a concise clinical context for the test, connections to commonly reported ICD-10 diagnoses associated with thyroid disorders, and links to related laboratory codes such as total thyroxine and thyroid hormone uptake. The publication summarizes typical sites of service and common clinical indications, outlines where 84439 fits within laboratory service lines, and identifies associated procedural neighbors used in thyroid panels.
This resource provides operational clarity for coding teams, billing staff, and clinical administrators seeking a national-level reference for the code’s clinical role, common diagnostic associations, and related laboratory services. Data not available in the input is noted where applicable.
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Billing Code Overview
CPT code 84439 describes a laboratory assay measuring free thyroxine (free T4), typically performed on patient serum. The service involves analytic measurement by a clinical laboratory analyst to assess circulating unbound T4 levels, which reflect thyroid hormone available to tissues.
Service type: Laboratory diagnostic test
Typical site of service: Clinical laboratory or hospital outpatient laboratory
National Reimbursement Benchmarks
National commercial pricing for CPT 84439 centers around BUCA’s average commercial benchmark of $24.8, with Blue Cross Blue Shield showing the highest dispersion and outliers — BCBS’s 75th–25th interquartile range is $17.4 ($43.0 − $27.6), reflecting substantial upward variability and a long upper tail (max $164.7). Aetna and Cigna show moderate central tendencies but differ in spread: Aetna’s IQR is $6.9 ($12.7 − $6.8), while Cigna’s IQR is $7.9 ($13.0 − $5.1), indicating relatively tighter clustering around their medians compared with BCBS.
UnitedHealth Group displays the tightest interquartile spread at $5.0 ($9.0 − $4.0), suggesting more consistent commercial reimbursement levels near its median of $5.40. Overall, payers vary notably in dispersion: Blue Cross Blue Shield is the widest, UnitedHealth Group the tightest, and BUCA’s mean positions it above several payers’ medians, highlighting a mid-to-upper commercial benchmark for this code.