Biochemical Investigations for Hyperandrogenism

The Goal: Measuring Androgen Excess

While clinical signs like hirsutism strongly suggest hyperandrogenism, biochemical testing provides objective, measurable evidence. The goal is to detect elevated levels of androgens in the bloodstream, a state known as hyperandrogenemia.

The primary androgen we are interested in is testosterone. However, measuring it isn't as simple as getting a single number. To truly understand its impact, we need to consider its different forms in the blood.

Total vs. Free Testosterone: The Role of SHBG

In the bloodstream, most testosterone is bound to proteins, primarily Sex Hormone-Binding Globulin (SHBG) and, to a lesser extent, albumin. Only a small fraction (about 1-2%) circulates as free testosterone, which is unbound and biologically active. It is this free testosterone that can enter cells and exert its effects on tissues like hair follicles and sebaceous glands.

• Total Testosterone (TT): Measures both bound and free testosterone.
• Free Testosterone (FT): Measures only the active, unbound form.
• Sex Hormone-Binding Globulin (SHBG): A protein produced by the liver that acts as a transport vehicle for testosterone. Think of it as putting testosterone "in storage," making it inactive.

In PCOS, two things often happen simultaneously:

1. The ovaries produce more testosterone, potentially raising the total testosterone level.
2. Factors like insulin resistance (which we will cover later) suppress the liver's production of SHBG.

With less SHBG available, a larger proportion of the total testosterone becomes "free" and active. This means a woman with PCOS can have significant hyperandrogenic symptoms even with a normal or only mildly elevated total testosterone level.

To get a clearer picture of this dynamic, the following short video provides an excellent explanation of SHBG and its clinical importance in PCOS.

Calculating Bioavailability: The Free Androgen Index (FAI)

Because directly measuring free testosterone can be technically complex and expensive, clinicians often use a calculation called the Free Androgen Index (FAI). It's a reliable estimate of androgen bioavailability.

The FAI is calculated with a simple formula:
$\text{FAI}=\left(\frac{\text{Total Testosterone level}}{\text{SHBG level}}\right)\times 100$
A high FAI, even with normal total testosterone, is a strong indicator of biochemical hyperandrogenism.

The Diagnostic Strategy: A Step-wise Approach

International guidelines recommend a structured, step-wise approach to testing for hyperandrogenism. This ensures efficiency and accuracy.

As the article you just read outlines, the strategy is as follows:

1. First-Line Tests:
These are the initial and most important tests. A positive result here is often sufficient to confirm biochemical hyperandrogenism.

• Total Testosterone (TT)
• Calculated Free Testosterone (cFT) or Free Androgen Index (FAI)

2. Second-Line Tests:
If the first-line tests are normal but clinical signs of hyperandrogenism are strong, the investigation can be expanded.

• Androstenedione (A4): A precursor to testosterone produced by both the ovaries and adrenal glands.
• Dehydroepiandrosterone Sulfate (DHEAS): An androgen produced almost exclusively by the adrenal glands. A high level might suggest an adrenal source of androgen excess.

This step-wise approach is also clearly described in the clinical practice paper, "Diagnosis and management of polycystic ovarian syndrome." Section 3, titled "Biochemical hyperandrogenism," confirms this testing hierarchy.

Differential Diagnosis: Ruling Out Other Conditions

A crucial role of biochemical testing is to differentiate PCOS from other, more serious conditions that can also cause hyperandrogenism.

Androgen-Secreting Tumors

While rare, tumors of the ovary or adrenal gland can produce massive amounts of androgens, leading to severe and rapidly progressing symptoms (e.g., voice deepening, clitoromegaly).

The Key Clue: The degree of testosterone elevation.

• PCOS: Characterized by mild to moderate elevation of androgens.
• Tumor: Suspected with markedly elevated androgen levels.

The following video explains this important distinction and provides a useful clinical cutoff.

Non-Classic Congenital Adrenal Hyperplasia (NCAH)

NCAH is a genetic condition that closely mimics the symptoms of PCOS. It is caused by a deficiency of an enzyme, usually 21-hydroxylase, in the adrenal glands. This deficiency disrupts the production of cortisol and shunts precursor molecules into the androgen synthesis pathway.

Fortunately, a single blood test can reliably distinguish NCAH from PCOS:

• 17-hydroxyprogesterone (17-OHP): This is the precursor molecule that builds up when 21-hydroxylase is deficient.
  • In NCAH: 17-OHP levels are high.
  • In PCOS: 17-OHP levels are normal.

Because the symptoms can be identical, testing 17-OHP is a mandatory step in the workup for PCOS. The video from MedSchool Simplified provides a superb, detailed explanation of this biochemical pathway.

Summary of Biochemical Investigations

To bring everything together, let's review the complete panel of initial investigations for a patient with suspected PCOS. This table summarizes the tests, their purpose, and what the results might indicate.

A few practical points to remember from this resource:

• Timing: These hormone tests should ideally be performed in the early follicular phase (days 2-4) of the menstrual cycle, if the patient is having cycles.
• Contraceptives: Hormonal contraceptives must be stopped for at least 3 months before testing, as they alter SHBG and androgen levels, making the results unreliable.

Conclusion

Today, we have thoroughly mapped out the biochemical strategy for confirming hyperandrogenism in PCOS. This process is not just about confirming a diagnosis but is a critical exercise in differential diagnosis.

Key Takeaways:

• Biochemical confirmation of hyperandrogenism relies on measuring total and free testosterone, often estimated using the Free Androgen Index (FAI).
• Low SHBG is a key feature in PCOS that increases the bioavailability of testosterone.
• The recommended approach is step-wise: first-line tests are Total T and Free T/FAI, while second-line tests include DHEAS and Androstenedione.
• Interpreting the level of elevation is crucial: mild-to-moderate elevation suggests PCOS, while marked elevation points towards a possible androgen-secreting tumor.
• A 17-hydroxyprogesterone (17-OHP) test is essential to rule out Non-Classic Congenital Adrenal Hyperplasia (NCAH), which can mimic PCOS.

Preview of the Next Lesson:

We have now covered all three components of the Rotterdam criteria: ovulatory dysfunction, clinical hyperandrogenism, and now biochemical hyperandrogenism. Our next lesson will focus on the last piece of the diagnostic puzzle mentioned in the criteria: the appearance of the ovaries themselves. You will learn to describe the role and interpretation of pelvic ultrasound in diagnosing polycystic ovarian morphology (PCOM).