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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.
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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)
National Reimbursement Benchmarks
National commercial reimbursements for CPT 84436 cluster around BUCA’s average commercial rate of $19.70, with variation across major carriers. Blue Cross Blue Shield shows a high mean and median ($29.50 and $27.40) while Aetna, Cigna, and UnitedHealth Group sit substantially lower (means $6.50, $7.60, and $6.00 respectively). BUCA’s mean of $19.70 represents an intermediate commercial benchmark between the lower-paying national commercial carriers and the outlying higher Blue Cross Blue Shield rates.
Dispersion measured as P75 minus P25 highlights where rates are tightest or widest: Aetna’s interquartile range is $2.90 ($7.90 - $5.00), Cigna’s is $5.40 ($10.00 - $4.60), UnitedHealth Group’s is $3.90 ($6.90 - $3.00), Blue Cross Blue Shield’s is $14.20 ($36.70 - $22.50), and BUCA’s is $9.80 ($24.50 - $14.70). Blue Cross Blue Shield shows the widest IQR, Aetna the tightest.