Laboratory Findings in Polycystic Ovary Syndrome (PCOS)
PCOS laboratory tests typically show elevated total testosterone as the most common abnormality, present in 70% of cases, along with an elevated LH/FSH ratio, low progesterone, and markers of insulin resistance. 1
Key Laboratory Abnormalities in PCOS
Hormonal Profile
- Total testosterone: Elevated in 70% of PCOS cases (>2.5 nmol/L) - most frequently abnormal marker 1, 2
- LH/FSH ratio: Often elevated (>2), but only abnormal in 41-44% of cases 1, 2
- Free Androgen Index (FAI): 78% sensitivity, 85% specificity 1
- Androstenedione (A4): Elevated in 53% of cases, with 75% sensitivity, 71% specificity 1, 2
- Dehydroepiandrosterone sulfate (DHEAS): 75% sensitivity, 67% specificity 1
- Calculated bioavailable testosterone: 76% sensitivity, 83% specificity (cutoff of 0.78 nmol/L) 1
- Progesterone: Often low (<6 nmol/L) indicating anovulation 1
Metabolic Parameters
- Glucose/insulin ratio: Often abnormal (<4), indicating insulin resistance 1
- Fasting insulin: May be elevated 3
- Glucose tolerance: May show impaired glucose tolerance or insulin resistance 3
First-Line Laboratory Tests for PCOS Diagnosis
The Endocrine Society recommends the following first-line tests 1:
- Total testosterone
- Free testosterone
- Thyroid-stimulating hormone (TSH)
- Prolactin
- 17-hydroxyprogesterone
Diagnostic Considerations
Diagnostic Accuracy
- Best single hormonal marker: Total testosterone (70% sensitivity) 2
- Best combination: Testosterone, androstenedione, and LH (abnormal in 86% of PCOS cases) 2
- Caution with LH/FSH ratio: Despite historical emphasis, this has low sensitivity and should not be used as the sole diagnostic criterion 2
Ultrasonographic Correlation
Laboratory findings should be correlated with ultrasonographic features, which may include:
- Increased follicle number per ovary (FNPO) - most accurate diagnostic marker (84% sensitivity, 91% specificity) 4
- Increased ovarian volume (OV) (81% sensitivity, 81% specificity) 4
- Increased follicle number per single cross-section (FNPS) (81% sensitivity, 83% specificity) 4
Common Pitfalls and Caveats
Assay variability: Different assays for the same hormone can yield significantly different results, particularly for LH and FSH 2
Timing of tests: Hormonal measurements should ideally be taken in the early follicular phase (days 2-5) of the menstrual cycle in women who are menstruating 2
SHBG considerations: Sex hormone-binding globulin levels are often influenced by body mass index, showing a negative correlation with BMI in women with PCOS 2
Anti-Müllerian Hormone (AMH): While not yet standardized for routine clinical use, AMH is typically elevated in PCOS and may eventually replace ultrasound for PCOM detection once standardization issues are resolved 4
Adolescent testing: Laboratory interpretation may differ in adolescents, as normal ranges can overlap with PCOS values in this age group 4
Differential Diagnosis Considerations
When interpreting laboratory results, consider other conditions that may present with similar findings:
- Functional hypothalamic amenorrhea: Typically has LH/FSH ratio <1 in 82% of cases, unlike PCOS 1
- Thyroid disorders: Abnormal TSH should prompt further thyroid evaluation
- Hyperprolactinemia: Elevated prolactin may indicate pituitary disorders rather than PCOS
- Congenital adrenal hyperplasia: Elevated 17-hydroxyprogesterone may indicate this condition rather than PCOS
By combining clinical features, laboratory findings, and ultrasonographic evaluation, a comprehensive assessment for PCOS can be achieved, with total testosterone being the most reliable single laboratory marker.