Interpretation of Laboratory Values in a 44-Year-Old Woman
These laboratory values indicate low-normal testosterone levels with normal SHBG, resulting in low free testosterone that may suggest androgen deficiency, particularly if accompanied by clinical symptoms of hypogonadism.
Laboratory Value Analysis
Total Testosterone Assessment
- Total testosterone of 7 ng/dL is at the very low end of the normal female range 1
- Reference ranges for a typical 30-40 year old woman show the 5th to 95th percentiles are 15-46 ng/dL, making this value below the 5th percentile 1
- Testosterone exhibits age-related decline in premenopausal women, but this level remains notably low even accounting for age 1
SHBG Interpretation
- SHBG of 40.6 nmol/L falls within the normal reference range (18-86 nmol/L for premenopausal women) 1
- Normal SHBG indicates that binding protein abnormalities are not artificially lowering free testosterone availability 2
Free Testosterone Evaluation
- Free testosterone of 1.1 pg/mL is at the lower limit of normal 1
- The reference range for free testosterone in a 30-year-old woman is 1.2-6.4 pg/mL, placing this value just below the 5th percentile 1
- Free testosterone measurement is more clinically relevant than total testosterone as it represents the biologically active hormone fraction 2, 3
Free Androgen Index (FAI)
- The percentage of free testosterone (1.6%) can be used to calculate FAI 4
- FAI is calculated as (Total Testosterone/SHBG) × 100 4, 3
- Using the provided values: (7/40.6) × 100 = 17.2, which is within normal range 4
- However, FAI correlates with free testosterone but is less accurate at extremes of SHBG concentration 2
Clinical Significance
When to Suspect Androgen Deficiency
Measure these values in the context of specific symptoms and risk factors 5:
- Sexual symptoms: Reduced libido or sex drive 5
- Physical symptoms: Persistent fatigue, reduced energy and endurance, diminished physical performance 5
- Cognitive/mood symptoms: Depression, reduced motivation, poor concentration, impaired memory, irritability 5
- High-risk conditions: Chronic corticosteroid use, pituitary dysfunction, unexplained anemia, bone density loss 5
Diagnostic Approach
- Obtain two separate morning measurements using the same laboratory methodology to confirm low testosterone 5
- The single measurement provided requires confirmation before establishing a diagnosis 5
- Free testosterone measurement is particularly important when total testosterone is near the lower limit of normal, as in this case 5, 2
- Calculated free testosterone using mass action equations correlates well with equilibrium dialysis (r = 0.99) and is preferred over direct immunoassay methods 3
Important Caveats
Measurement Considerations
- Testosterone exhibits diurnal variation; samples should be collected in the morning 5
- Assay standardization remains challenging, and results may vary between laboratories 6
- Free testosterone measurement by equilibrium dialysis is the gold standard, but calculated free testosterone is acceptable when using validated assays 2, 3
Context-Specific Interpretation
- These values alone do not establish a diagnosis of androgen deficiency without clinical correlation 5
- In women with menstrual irregularity, additional evaluation for conditions like PCOS, hypothalamic amenorrhea, or hyperprolactinemia should be considered 4
- If symptoms of androgen deficiency are present, these borderline-low values support the diagnosis and may warrant further endocrine evaluation 5