84402

Testosterone; free

CPT code 84402 represents the laboratory measurement of free testosterone in a patient's blood serum or plasma. Testosterone is the primary male sex hormone, although it is present and physiologically significant in females as well. In the bloodstream, testosterone exists in three distinct states: approximately 60% to 80% is tightly bound to sex hormone-binding globulin (SHBG), about 20% to 40% is weakly bound to albumin, and only 1% to 2% remains 'free' or unbound. The sum of these three components is measured as total testosterone (CPT 84403). However, total testosterone levels can be misleading in patients with conditions that alter SHBG levels, such as obesity, liver disease, thyroid dysfunction, or the use of certain medications like glucocorticoids or estrogens. In these scenarios, the free testosterone level (84402) provides a more accurate reflection of the biologically active hormone available to tissues. The measurement of free testosterone is clinically superior for diagnosing androgen deficiency (hypogonadism) in men or androgen excess (such as in polycystic ovary syndrome or hirsutism) in women when total testosterone results are borderline or inconsistent with clinical symptoms. The laboratory methodology for 84402 often involves equilibrium dialysis, which is considered the gold standard, or ultrafiltration, to separate the unbound hormone from the protein-bound fractions before quantification by highly sensitive assays like liquid chromatography-tandem mass spectrometry (LC-MS/MS). Accurate reporting of this code ensures precise diagnostic pathways for complex endocrine disorders.

Clinical Indications

  • Evaluation of suspected male hypogonadism when total testosterone is low-normal.
  • Assessment of androgen excess in females presenting with hirsutism or virilization.
  • Diagnostic workup for Polycystic Ovary Syndrome (PCOS).
  • Monitoring of testosterone replacement therapy (TRT) to ensure bioavailable levels are within therapeutic ranges.
  • Evaluation of male infertility or erectile dysfunction.
  • Investigation of delayed or precocious puberty in pediatric patients.
  • Monitoring patients with conditions known to alter SHBG levels, such as cirrhosis or nephrotic syndrome.
  • Assessment of decreased libido or unexplained fatigue in both males and females.

Procedure Steps

  1. A peripheral venous blood sample is collected from the patient, typically in a serum separator tube (SST) or plain red-top tube.
  2. The specimen is centrifuged to separate the serum from the cellular components.
  3. The serum is transferred to a transport vial and maintained at refrigerated temperatures (2-8°C).
  4. In the laboratory, the free fraction is separated from protein-bound testosterone, most commonly using equilibrium dialysis or centrifugal ultrafiltration.
  5. The concentration of the free testosterone in the resulting dialysate or ultrafiltrate is measured using a sensitive immunoassay or liquid chromatography-tandem mass spectrometry (LC-MS/MS).
  6. The laboratory technician verifies the results against established reference ranges based on the patient's age and sex.
  7. The final concentration is reported in pg/mL or ng/dL.

Coding Guidelines

  • CPT 84402 specifically identifies the measurement of the 'free' fraction only.
  • Do not report 84402 in conjunction with 84403 (Total Testosterone) unless both assays are medically necessary and performed distinctly; however, they are often ordered together as a panel.
  • If 'Bioavailable' testosterone is measured (which includes both free and albumin-bound), use CPT 84410 instead of 84402.
  • Check individual payer policies regarding the frequency of testing for hormone monitoring.
  • If the free testosterone is calculated from total testosterone and SHBG rather than directly measured by dialysis, some payers may require different reporting or consider it inclusive of the primary tests.

Associated ICD-10 Codes