Interpreting Hormone Laboratory Tests
When interpreting hormone laboratory tests, clinicians should consider the specific assay generation used, laboratory-specific reference ranges, and the patient's clinical context, as these factors significantly impact result interpretation and subsequent clinical decisions.
General Principles for Hormone Test Interpretation
Laboratory values should be interpreted in the context of the specific assay used, as different assay generations may measure different hormone fragments or modified forms, leading to significant variations in results 1.
For serial measurements of hormones (such as PTH), use the same assay in the same laboratory to ensure accurate trend assessment, as switching between assays can lead to misleading interpretations 1.
Reference ranges are laboratory-specific and should not be considered absolute cutoff values across different testing facilities 1.
Pre-analytical variables (such as fixative type, time to fixation, and duration of fixation) should be documented and considered when interpreting results 1.
Hormone-Specific Interpretation Guidelines
Thyroid Function Tests
For thyroid function tests, clinicians should be aware that subclinical thyroid disease is defined by abnormal TSH with normal T4 and T3 levels in asymptomatic individuals without history of thyroid dysfunction 1.
When monitoring levothyroxine therapy in adults with primary hypothyroidism, assess TSH levels 6-8 weeks after any dosage change, and evaluate clinical and biochemical response every 6-12 months once stable 2.
In pediatric patients on levothyroxine, monitor TSH and total or free-T4 at 2 and 4 weeks after treatment initiation, 2 weeks after any dosage change, and then every 3-12 months after dosage stabilization 2.
For secondary and tertiary hypothyroidism, monitor serum free-T4 levels and maintain in the upper half of the normal range 2.
Parathyroid Hormone (PTH)
When interpreting PTH results, consider the assay generation used - second-generation assays typically measure higher PTH concentrations compared to third-generation assays due to differences in fragment detection 1.
For perioperative PTH monitoring during parathyroidectomy, third-generation assays show more rapid decrease in PTH concentrations and may be more useful for assessing surgical success 1.
Avoid using absolute cutoff values for PTH across different laboratories; instead, rely on laboratory-specific reference ranges 1.
Estrogen and Progesterone Receptors
For estrogen receptor (ER) testing in breast cancer, consider both the percentage of cancer cells staining and stain intensity 1:
- Report as ER positive if >10% of cells stain with moderate or strong intensity
- Report as ER negative if ≤10% of cells stain OR intensity is weak
- Report as ER low positive if 1-10% of cells stain, with appropriate cautionary comments 1
For progesterone receptor (PgR) testing, interpret as positive if 1-100% of cells have nuclear staining or negative if <1% of cells have nuclear staining 1.
Ensure that external and internal controls stain appropriately before interpreting results 1.
Special Populations
Transgender and Gender-Diverse Individuals
For transgender individuals on gender-affirming hormone therapy (GAHT) for more than 1 year, many laboratory values should be interpreted based on their affirmed gender 1.
For those newly initiated on hormone therapy (<1 year), understand that values may change over time 1.
For individuals who have stopped GAHT, laboratory values typically reflect their sex assigned at birth within 3 months 1.
For renal function assessment in transgender individuals, consider using cystatin C as it is less dependent on muscle mass and dietary intake than creatinine 1.
If cystatin C is unavailable, recent practice supports using the creatinine reference range based on the person's affirmed gender for those on established GAHT 1.
Common Pitfalls and How to Avoid Them
Be aware that hormone assays can be affected by heterophile antibodies, biotin interference, and cross-reactivity, which may lead to falsely elevated or decreased results 3.
For PTH measurements, recognize that different assay generations measure different fragments, which can lead to significant variations in results (up to 47%) 1.
When interpreting hormone ratios, consider their inherent statistical limitations and asymmetry; non-parametric methods or log-transformation may be more appropriate for analysis 4.
For serial monitoring of hormone levels, ensure consistency in the laboratory, assay method, and collection timing to avoid misinterpretation of trends 1.
Consider the impact of medications, supplements, and sample collection timing on hormone test results 3.