In a woman with polycystic ovary syndrome who has blood drawn in the afternoon, can a fasting sample still be used for testosterone measurement, and is a morning draw preferred for the most accurate assessment of hyperandrogenism?

Testosterone Testing Timing in PCOS Women

For women with PCOS, testosterone should ideally be drawn in the morning (before 10 AM) in a fasting state, as this provides the most accurate assessment of hyperandrogenism, though afternoon samples can still be used with the understanding that testosterone levels may be slightly lower due to diurnal variation.

Why Morning Draws Are Preferred

• Testosterone exhibits diurnal variation with highest levels in the early morning and gradual decline throughout the day, making morning samples (ideally 8-10 AM) the standard for accurate assessment 1
• The 2023 International PCOS Guidelines recommend measuring testosterone in the morning using liquid chromatography-tandem mass spectrometry (LC-MS/MS) for highest accuracy 1, 2
• Morning timing is particularly important when testosterone levels are borderline, as afternoon values may fall below diagnostic thresholds even when true hyperandrogenism exists 1

Can Afternoon Samples Still Be Used?

Yes, afternoon samples remain clinically useful, but with important caveats:

• Total testosterone (TT) and free testosterone (FT) can be measured in afternoon samples, though values may be 10-25% lower than morning levels due to normal diurnal rhythm 3
• If afternoon testosterone is elevated, it confirms hyperandrogenism regardless of timing 4
• If afternoon testosterone is normal but clinical suspicion remains high (hirsutism, acne, oligomenorrhea), repeat testing in the morning is warranted before excluding biochemical hyperandrogenism 1, 2

Fasting Requirements

• Fasting is required for metabolic screening (glucose tolerance test, lipid panel) which should be performed concurrently in all PCOS patients 5
• Testosterone measurement itself does not require fasting, but fasting samples are preferred when drawing comprehensive PCOS workup to assess insulin resistance and metabolic complications 5, 6
• The ACOG recommends fasting glucose followed by 2-hour glucose tolerance test with 75-gram glucose load for all PCOS patients due to increased diabetes risk 5

Optimal Testing Strategy

First-line androgen testing should include:

• Total testosterone (TT) by LC-MS/MS: sensitivity 74%, specificity 86% 5, 4
• Free testosterone (FT) by equilibrium dialysis or calculated free androgen index (FAI): sensitivity 89%, specificity 83% for calculated FT 5, 4
• Sex hormone-binding globulin (SHBG) to calculate FAI when LC-MS/MS unavailable 5, 7

If first-line androgens are normal but clinical suspicion remains high:

• Measure androstenedione (A4): sensitivity 75%, specificity 71% 5, 4, 2
• Measure DHEAS: sensitivity 75%, specificity 67% 5, 4, 2

Critical Pitfalls to Avoid

• Do not use direct immunoassay methods for free testosterone - these are highly inaccurate at low female ranges and should be avoided entirely 5, 1, 8
• Do not rely on total testosterone alone - approximately 30% of PCOS women have normal total testosterone but elevated free testosterone or FAI 2, 7
• Do not dismiss afternoon values if elevated - elevated afternoon testosterone still confirms hyperandrogenism 3
• Do not order ultrasound as sole diagnostic criterion - polycystic ovarian morphology appears in up to one-third of normal women and requires biochemical or clinical hyperandrogenism plus ovulatory dysfunction for PCOS diagnosis 2, 8

Concurrent Metabolic Screening

All PCOS patients require fasting metabolic assessment regardless of testosterone timing:

• Fasting glucose and 2-hour oral glucose tolerance test (75g glucose load) 5
• Fasting lipid panel including total cholesterol, LDL, HDL, and triglycerides 5
• TSH to exclude thyroid disease 5, 1
• Prolactin to exclude hyperprolactinemia 5, 1

Practical Clinical Algorithm

If blood drawn in afternoon:

1. Proceed with testosterone measurement (TT, FT/FAI) plus metabolic screening 4, 1
2. If testosterone elevated → confirms hyperandrogenism, no repeat needed 4
3. If testosterone normal but strong clinical features (hirsutism, severe acne, oligomenorrhea) → repeat morning draw before excluding biochemical hyperandrogenism 1, 2
4. If morning repeat also normal → measure second-line androgens (A4, DHEAS) 5, 4, 2

Optimal approach for new PCOS evaluation:

• Schedule morning (8-10 AM) fasting blood draw to capture both androgen assessment and metabolic screening in single visit 1, 2
• This maximizes diagnostic accuracy and patient convenience while meeting all guideline recommendations 5, 4