Testosterone, Free

Alternative Names
  • Free Testosterone, Direct

Test Code: 4024

CPT:
Tests Included Testosterone, SHBG
Use In recent years the diagnosis of Low T has favored the use of Free Testosterone, which is the portion (~3-4%) in blood not bound to sex hormone binding globulin (SHBG), and to a lesser extent to albumin. The amount of testosterone that is bound is very consistent, so Free T can be calculated (instead of directly measured). This calculation is based on measurement of total testosterone, SHBG, and albumin.
Clinical Utility An abnormally low total testosterone level in males can be indicative of hypogonadism, hypopituitarism, hyperprolactinemia, renal failure, hepatic cirrhosis, or Kleinfelter's syndrome. Men experiencing symtopms of low T and using opioid medications for >90 can exhbit Opioid Induced Androgen Deficiency (OPIAD).  High total testosterone values in males can be caused by adrenal and testicular tumors, congenital adrenal hyperplasia or abnormalities of the hypothalamic-pituitary-testicular axis.1

Increased female total testosterone levels may indicate polycystic ovary syndrome (PCOS), stromal hyperthecosis, ovarian and adrenal tumors, congenital adrenal hyperplasia and other disorders of the hypothalamic-pituitary-ovarian axis.2
Intended Patient Population 18+ and Older Adult Males
Patient Preparation None Specified
Sample Serum, Plasma
Tube Red, Green, Tiger
Volume 4mL Whole Blood (1mL Serum/Plasma)
Min Sample Volume 0.5 mLs
Reference Ranges Testo - M 18-39 yrs old; 300-1080 ng/dL
Testo - M 40-59 yrs old; 300-890 ng/dL
Testo - M 60-150 yrs old; 300-720 ng/dL
SHBG - M ≥ 18 yrs old;  11-80 nmol/L
Free Testo (calc) M ≥ 18 yrs old;  4.7-24.4 ng/dL
Analytical Measurement Range Testo - 6.25-1600.00 ng/dL
SHBG - 0.161-200 nmol/L
Units ng/dL
Test Methodology LC/MS/MS &
Chemiluminescent Immunoassay
Test Turnaround Time 5 Days
Limitations None Specified
Shipping Requirements Refrigerated
Specimen Stability 7 Days RT
4 Days RF
Reject Criteria 0
Laboratory Developed Test (LDT) Yes
CMS Guidance None
References
  1. Wilson, JD, Foster, DW (Eds) Williams Textbook of Endocrinology, 8th Edition, W.B. Saunders, Philadelphia, Pennsylvania 19106, 1992, page 822-832.
  2. Brutis, CA, Ashwood, ER (Eds) Tietz Fundamentals of Clinical Chemistry, 4th Edition W.B. Saunders, Philadelphia, Pennsylvania 19106, 1996, page 671 - 672.

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