Summary & Overview
CPT 84442: Thyroxine Binding Globulin (TBG) Assay, Serum
CPT code 84442 denotes a laboratory assay measuring thyroxine binding globulin (TBG) in patient serum. TBG measurement helps contextualize total thyroxine (T4) results by identifying variations in thyroid hormone–binding proteins that can alter total hormone concentrations without reflecting true thyroid dysfunction. Nationally, this test is used in endocrine evaluation, medication monitoring, and select diagnostic workups where altered binding capacity is suspected.
Key payers covered in this analysis include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find a concise overview of clinical context for TBG testing, typical sites of service, and what to expect from coding and billing perspectives. The report outlines common billing modifiers and payer coverage considerations where available, and highlights benchmarking and policy implications relevant to laboratory service lines.
This summary provides practical context for administrators, laboratory directors, and billing professionals seeking to align testing utilization with coding guidance and payer practices. Data not available in the input is noted where applicable in detailed sections.
Billing Code Overview
CPT code 84442 describes a laboratory assay performed by a medical laboratory analyst to measure thyroxine binding globulin (TBG), typically using a patient's serum sample. The test quantifies the concentration of the carrier protein that binds thyroxine (T4), providing context for thyroid function testing and interpretation of total thyroid hormone levels.
Service Type: Clinical laboratory test — serum protein assay
Typical Site of Service: Clinical laboratory or hospital laboratory (inpatient or outpatient specimen processing)
Clinical & Coding Specifications
Clinical Context
A 34-year-old woman presents to an outpatient laboratory after evaluation for abnormal thyroid function tests and symptoms of fatigue and weight changes. Her clinician orders measurement of thyroxine-binding globulin to help interpret total thyroxine (T4) levels and assess whether abnormal total T4 reflects altered binding protein concentration rather than true free thyroid hormone excess or deficiency. A phlebotomy technician collects a serum sample, which is sent to the clinical laboratory. A medical laboratory scientist performs the 84442 assay (measurement of thyroxine binding globulin) using an immunoassay or other validated method. Results are reported in μg/mL or appropriate units and routed to the ordering clinician for correlation with total T4, free T4, TSH, and clinical findings. Typical sites of service include hospital outpatient laboratories, independent clinical laboratories, and inpatient hospital laboratories when thyroid function interpretation is necessary.
Coding Specifications
| Modifier | Description | When to Use |
|---|---|---|
26 | Professional component | Use when billing only the professional interpretation component if applicable (rare for 84442). |