Recommends mass spectrometry for research purposes and good-quality immunoassays for routine clinical diagnosis when standardized against an international reference range. Triggers when a clinician orders a testosterone test and asks "which assay should I use?" or questions "is this immunoassay reliable enough?"
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---
name: icsm-choose-testosterone-assay-method
description: Recommends mass spectrometry for research purposes and good-quality immunoassays for routine clinical diagnosis when standardized against an international reference range. Triggers when a clinician orders a testosterone test and asks "which assay should I use?" or questions "is this immunoassay reliable enough?"
---
# Select appropriate testosterone assay method for diagnosis
## STEP 1 — Gather Information
Determine assay purpose (research vs clinical), verify sample timing (fasting, 07:00–11:00), identify assay platform (mass spectrometry or immunoassay), and check if immunoassay is standardized against an internationally harmonized reference range.
## STEP 2 — Rule In / Rule Out
Is the assay intended for research?
- **Yes** → proceed to Step 3 for research preference.
- **No** (clinical diagnosis) → proceed to Step 3 for clinical acceptability.
## STEP 3 — Classify or Stratify
For research: mass spectrometry is the gold standard.
For clinical: Is the immunoassay good-quality and standardized against an international reference range?
- **Yes** → immunoassay acceptable for diagnosis.
- **No** → immunoassay not reliable; consider mass spectrometry or send sample to a certified reference lab.
## STEP 4 — Decide
- **Research**: Use mass spectrometry.
- **Clinical & standardized immunoassay**: Use the immunoassay.
- **Clinical & non‑standardized immunoassay**: Use mass spectrometry or refer sample to a lab with a validated, standardized assay.
## Clinical Guardrails / Mimics / Pitfalls
Do not rely on non‑standardized immunoassays for diagnostic decisions; avoid using immunoassay results without verification of standardization; do not substitute immunoassay for mass spectrometry in research settings; avoid testosterone measurement during acute illness; ensure fasting morning sample collection.
## Concrete Clinical Example
A 45‑year‑old man presents with low libido and fatigue. The clinician orders a morning testosterone test, confirms the hospital immunoassay is CDC‑harmonized and calibrated to the international reference range, and proceeds with the immunoassay for clinical diagnosis.
**Source:** Male hypogonadism: recommendations from the Fifth International Consultation on Sexual Medicine (ICSM 2024), International Society for Sexual Medicine, 2025, DOI: 10.1093/sxmrev/qeaf036
