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Not medical advice. The Atlas is not a substitute for a clinician who can examine you.

LC-MS/MS vs Immunoassay

Why how testosterone is measured changes the answer

Evidence grade 5 of 5, Settled. Read how the Atlas grades evidence.

The written rationale for this grade is still being prepared.

FDA
Not applicable (assay methodology)

Reference only. Not medical advice.

This is something to take to a clinician. The Atlas can tell you what is known about lc-ms/ms vs immunoassay in general. It cannot tell you what is happening in your body, and the difference matters most for exactly the symptoms that bring people to this page.

How a lab measures testosterone materially changes the result. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is the gold-standard method the Endocrine Society recommends: it physically separates and identifies testosterone with high accuracy and specificity. Most commercial labs, however, use cheaper automated immunoassays, which can over- or under-estimate testosterone by 20-30%, especially at the low and high ends and in the presence of cross-reacting steroids. This is a major, under-appreciated source of diagnostic error, a man can be labeled 'low' or 'normal' partly by which machine ran the sample.

Two men, same blood, different testosterone number, depending on the assay.

What it is invoked to explain

Claims this idea is used to support. Whether it supports them is the rest of the entry.

  • Explains lab-to-lab and method-to-method variability

How it works

LC-MS/MS separates testosterone chromatographically and detects it by mass-to-charge ratio, minimizing interference. Immunoassays use antibodies that can cross-react with structurally similar steroids and are less accurate at low concentrations (relevant for women, children, and hypogonadal men). The CDC's Hormone Standardization (HoSt) program exists partly to harmonize these methods.

What people get wrong

  • Often saidA testosterone number is a testosterone number

    ActuallyThe same sample can read 20-30% different between an immunoassay and LC-MS/MS. Method matters, especially near diagnostic thresholds.

Who profits, and who pushes back

Nobody is named here yet, because we have not done that work on this entry. Read that as unfinished. Somebody almost certainly sells this, and somebody almost certainly disputes it. Assume both until we have checked.

At a glance

Gold standard
LC-MS/MS (Endocrine Society)
Common alternative
Automated immunoassay
Immunoassay error
Often 20-30%, worst at extremes

What this entry does not yet cover

What follows is unfinished work on our side, not a finding about LC-MS/MS vs Immunoassay. A short entry is not a safe entry.

  • Timeline. We have not built the dated record of research and regulatory events.
  • Cost and market. We have not documented what it sells for or who sells it.
  • Supply chain. We have not mapped where it is made.
  • Who uses it. We have not documented the user groups.
  • What could change. No forward-looking summary yet.
  • How it compares. We have not set it against the alternatives.
  • Children and teenagers. We have not checked what is known about younger people.
  • What can go wrong. We have not written the risk line for this one. Read the safety section below rather than treating its absence as reassurance.
  • Where we land. We have not taken a position on this yet.

Sources

The studies below are named and described, but not linked. You cannot open them from here and check our reading against them, which means this page is our summary of the literature rather than a document you can verify. Weigh it accordingly until the links exist.

The studies that matter

  • Endocrine Society / CDC HoSt standardization,

    Established LC-MS/MS as the reference method and created the Hormone Standardization program to harmonize assays