Summary & Overview
CPT 84436: Thyroxine (T4) Total Blood Test
CPT code 84436 identifies a laboratory assay for serum thyroxine (total T4), a central test in evaluating thyroid function and endocrine disorders. Nationally, measurement of T4 supports diagnosis and management of hypothyroidism, thyrotoxicosis, autoimmune thyroiditis and other thyroid-related conditions, making this code a routine component of outpatient and inpatient laboratory panels. Its use affects clinical decision-making, laboratory workflows, and payer reimbursement for endocrine testing.
Key payers considered in this overview include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. The discussion highlights common billing contexts and how this test is positioned among related thyroid assays, such as free T4 and TSH testing.
Readers will learn the clinical purpose of the test, typical sites of service, common diagnostic indications, and how CPT code 84436 relates to nearby thyroid procedure codes used in practice. The summary outlines benchmarking and coding context without prescribing clinical actions. It also identifies where this code sits in testing bundles and laboratory service lines, and notes related laboratory codes for thyroid evaluation. Data not available in the input is indicated where applicable.
Billing Code Overview
CPT code 84436 represents a laboratory test measuring thyroxine (T4) concentration in a patient's blood. The assay quantifies total T4 produced by the thyroid gland, a hormone involved in growth and development.
Service type: Laboratory testing — thyroid function assay
Typical site of service: Clinical laboratory or outpatient phlebotomy/ambulatory care setting (blood specimen collected via routine venipuncture)
Clinical & Coding Specifications
Clinical Context
A 48-year-old female presents to her primary care clinic with fatigue, weight gain, cold intolerance, and dry skin. The clinician orders a serum total thyroxine (T4) assay to assess thyroid hormone levels as part of initial thyroid function testing and to follow up an abnormal thyroid stimulating hormone (TSH) result. A phlebotomist performs routine venipuncture in the outpatient clinic or hospital laboratory; the specimen is transported to the clinical laboratory. The lab analyst performs the 84436 assay (total T4) using appropriate immunoassay methodology. Results are reported in the electronic medical record and interpreted by the ordering clinician or an endocrinologist to guide diagnosis and management for conditions such as E03.9 (hypothyroidism), E05.90 (thyrotoxicosis), E06.3 (autoimmune thyroiditis), or to evaluate abnormal thyroid function studies (R94.6). Typical sites of service include outpatient clinic, ambulatory care laboratory, hospital outpatient laboratory, and inpatient hospital laboratory depending on patient presentation and care setting.
Coding Specifications
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