Testosterone (Blood)

Diagnostic Use

The total testosterone level provides an adequate assessment of testosterone status in most cases.  In borderline cases free testosterone provides a slightly better estimate of androgen activity  than total testosterone, because changes in sex hormone binding globulin (SHBG) are incorporated into the calculation of free testosterone.  See  Testosterone – free (Blood).

Investigations for hirsutism in women  (ref. 1)

A testosterone level may be performed in the initial investigation of hirsutism, acne or menstrual irregularity.

Mild hirsutism of slow onset without other signs of androgen excess (acne, clitoromegaly or muscularity), menstrual irregularity or infertility does not require measurement of testosterone or any other androgen.

In women with moderate or severe hirsutism or hirsutism of any degree when it is sudden in onset, rapidly progressive, or associated with other abnormalities such as menstrual dysfunction, obesity, or clitoromegaly, a testosterone level is recommended.

If the testosterone level is raised, the commonest cause is PCOS.  To exclude other conditions the following investigations are suggested (1):

• measurement of prolactin, DHEAS (to exclude an adrenal tumour) and 17-hydroxyprogesterone (to exclude late-onset 21-hydroxylase deficiency)
• pelvic ultrasonography  to detect an ovarian neoplasm or a polycystic ovary

Mildly raised levels are consistent with PCOS or idiopathic hyperandrogenism.

Once a diagnosis has been made, repeated measurements of testosterone are not usually necessary or helpful.

Males

Primary hypogonadism is present if the testosterone is low, and LH and FSH are high.

Secondary hypogonadism is present if the testosterone is low  and LH and FSH are normal or low.

What is a normal level of serum testosterone in males?

The reference intervals shown above represent the central 95% of a normal population.

Large cross-sectional studies of serum testosterone in healthy adult males have shown a progressive decrease of total and free testosterone with age from 25 years onwards.

The relationship of testosterone level to sexual function is controversial. Symptoms of sexual dysfunction were associated with testosterone levels less than 8 nmol/L  in one study (5) while another found levels less than 11 nmol/L  were significantly associated with symptoms of sexual dysfunction (4).

In symptomatic patients with pituitary or hypothalamic disease, total testosterone values are typically < 8 nmol/l, and associated with other hormone deficiencies (such as a low or falling T4) or a raised serum prolactin.

Because of the diurnal variation (testosterone highest in the early morning), low results should be confirmed with an early morning sample.

Monitoring testosterone replacement: It is not usually necessary to monitor testosterone levels in patients recieving injections of depot testosterone (e.g. Sustanon). This may be helpful if the clinical response is poor, to confirm that an adequate testosterone level has been achieved.  After the injection there is a high level for several days, followed by a decline over 2 – 4 weeks, or longer depending on the preparation injected. For monitoring, a trough testosterone level should be obtained (i.e. before the next injection). The target trough level is 8 – 12 nmol/L. The interval between injections can be adjusted to achieve the target level.  Once the correct interval has been determined, further testosterone tests should not be necessary.

References

1. Martin KA, Chang RJ, Ehrmann DA et al. Evaluation and treatment of hirsutism in premenopausal women: an endocrine society clinical practice guideline. J Clin Endocrinol Metab. 2008;93:1105-1120
2. Soldin et al. Paediatric Reference Ranges, 3rd ed (1999)
3. Endocrine Sciences, Adrenal steroid responses to ACTH (in house publication, 1991)
4. Wu FC, Tajar A, Beynon JM et al. Identification of late-onset hypogonadism in middle-aged and elderly men. N Engl J Med 2010;363:123-135
5. O’Connor, D. B., D. M. Lee, et al. (2011). “The relationships between sex hormones and sexual function in middle-aged and older European men.” J Clin Endocrinol Metab 96(10): E1577-1587.

Reference Intervals

Units: nmol/L

•  Testosterone levels in males are highest in the morning, and decrease thereafter.  Reference intervals apply to pre-9 a.m. samples.