Immunoassay vs LC/MS Testosterone Tests: What the Method Means and Why the 1,500 Cap Matters

Two testosterone results can come from very different methods. Most people never see which one their lab used, but it can change how much a number tells you.

The short answer

A standard immunoassay measures testosterone with antibodies. It's fast, cheap and usually fine for screening an adult man who isn't on testosterone therapy. Some common immunoassays also stop reporting at 1,500 ng/dL, so any higher result comes back as ">1500."

LC/MS (liquid chromatography with tandem mass spectrometry, often written LC-MS/MS) separates testosterone from everything else in the sample and identifies it by mass. It's more specific, more accurate at low levels, and usually reports high values without a cap.

The method matters most if:

• You're on testosterone therapy, or your provider is adjusting treatment and needs an exact number.
• Your levels are low, as in women, adolescents and men with low testosterone, where immunoassays are least reliable.
• You track results over time and want each draw to be comparable.
• You take high-dose biotin, which can interfere with many immunoassays.

How the two methods work

Immunoassay

An immunoassay uses an antibody designed to bind testosterone. The lab measures how much binding happens and converts that into a concentration. Many large labs run automated immunoassays, such as electrochemiluminescence (ECLIA), on high-throughput analyzers. They're quick and inexpensive.

The trade-off is specificity. Antibodies can react a little with molecules shaped like testosterone, and accuracy drops at the low end of the range. In a 2007 position statement, the Endocrine Society said direct testosterone assays perform poorly at the low concentrations found in women, children and men with low testosterone, and should be avoided in those groups. [1]

LC/MS

LC/MS works in two steps. Liquid chromatography first separates the compounds in the sample, then the mass spectrometer identifies testosterone by its mass and how it breaks apart. That makes it much less likely to confuse testosterone with a similar molecule, and it holds up well at low concentrations. The same Endocrine Society statement pointed to mass spectrometry as the likely reference standard for testosterone measurement. [1]

LC/MS isn't automatically "right" and immunoassay "wrong." What matters is how well a specific assay is calibrated. The CDC runs a Hormone Standardization Program that certifies testosterone assays, both immunoassays and LC/MS, for accuracy. [2] For a typical adult man not on therapy, a well-calibrated immunoassay often lands close to an LC/MS result. The gaps show up at the extremes.

Why the 1,500 cap matters

Every assay has a reportable range, the span of values it can measure reliably. Labcorp's standard testosterone immunoassay (test 004226, an ECLIA test for screening adult men) has a reportable range of 12 to 1,500 ng/dL. [3] Results above the top of the range are reported as greater than 1,500, not as an actual number.

For most men who aren't on therapy, that's not a problem. A widely used harmonized reference range for healthy, non-obese men aged 19 to 39 is 264 to 916 ng/dL, well under the cap. [4]

It does become a problem in a few situations:

• On testosterone therapy. Levels can rise above 1,500, especially when blood is drawn near a peak. A result of ">1500" could mean 1,600 or 3,000, and those may call for different decisions from your provider.
• Tracking a protocol. If two draws both read ">1500," you can't tell whether a change moved your level up, down or not at all. A trend chart flattens into a line along the ceiling.
• Connecting markers. Very high testosterone can track with changes in hematocrit and estradiol. Without the real number, it's harder to see how they relate.

How to read a capped result: ">1500 ng/dL" means at least 1,500. Don't record it as exactly 1,500. If you or your provider need the real value, repeat the test with an uncapped LC/MS method.

Free testosterone: method matters even more

Most testosterone in blood is bound to proteins, mainly SHBG and albumin. Free testosterone is the small unbound fraction. The Endocrine Society's 2018 guideline recommends measuring free testosterone by equilibrium dialysis, or calculating it from total testosterone, SHBG and albumin. It recommends against direct "analog" immunoassays for free testosterone, which are known to be inaccurate. [5]

So when you compare panels, check both lines: how total testosterone is measured (immunoassay or LC/MS), and how free testosterone is measured (equilibrium dialysis, calculated, or direct immunoassay).

Biotin can throw off immunoassays

Many immunoassays use a biotin-based chemistry. The FDA has warned that high biotin levels in a blood sample can cause falsely high or falsely low results on affected tests. Many hair, skin and nail supplements contain biotin at many times the recommended daily intake. [6] LC/MS doesn't rely on that chemistry in the same way.

If you take a high-dose biotin supplement, tell your provider before a lab draw and ask whether to pause it.

The same question applies to estradiol

Men's estradiol levels are low, and standard estradiol immunoassays are least reliable at low concentrations. That's why many men, especially on testosterone therapy, use an ultrasensitive LC/MS estradiol test. For more, see sensitive estradiol testing for men.

Which testosterone tests Anabolic Insights offers

We label the method on every test so you can choose.

The Basic Panel is a good, low-cost baseline if you're not on therapy and expect a typical result. If you're on testosterone therapy, tracking a protocol, or want results you can compare cleanly over time, choose an LC/MS option. At Quest, a standalone LC/MS total testosterone test (test code 15983) is $14 as of October 2026. On that test's page, pick the Quest option to get that exact test.

How to choose

• Not on therapy, first baseline: an immunoassay panel is usually fine. If the result is near the top of the range or doesn't match how you feel, repeat it with LC/MS.
• On testosterone therapy, or your provider is adjusting treatment: use LC/MS for total testosterone, plus equilibrium dialysis or calculated free testosterone.
• Low levels expected (women, adolescents, men with suspected low testosterone): use LC/MS.
• Comparing draws over time: use the same method and the same lab every time, and draw at a consistent time of day. See whether testosterone labs should be drawn in the morning and peak vs trough timing on TRT.

Results are educational and don't replace an evaluation by a licensed provider. Treatment decisions should be made with your provider.

FAQs

What does it mean when a testosterone result says greater than 1500?

It means your level was at or above the highest value that assay can report, which for some common immunoassays is 1,500 ng/dL. Your actual level could be anywhere above that. If you need the exact number, retest with an uncapped LC/MS method.

Is LC/MS testosterone more accurate than immunoassay?

LC/MS is more specific and more reliable at low concentrations, and the Endocrine Society has pointed to mass spectrometry as the reference standard. For typical adult male levels, a well-calibrated, CDC-certified immunoassay often agrees closely with LC/MS. The biggest differences appear at low levels and above an immunoassay's reportable range.

Do I need LC/MS testosterone if I'm not on TRT?

Usually not for a first screening in an adult man. A standard immunoassay is often enough. Consider LC/MS if your levels are expected to be low, if your result is borderline, or if you want to compare future results precisely.

Why should people on testosterone therapy use LC/MS?

Levels on therapy can exceed 1,500 ng/dL, where some immunoassays stop reporting a real number. LC/MS gives an uncapped result, so you and your provider can see the actual level and compare draws over time.

How should free testosterone be measured?

The Endocrine Society recommends equilibrium dialysis, or calculating free testosterone from total testosterone, SHBG and albumin. It recommends against direct analog immunoassays for free testosterone.

Can biotin affect testosterone results?

Yes, on many immunoassays. The FDA has warned that high biotin levels can cause falsely high or falsely low results on affected tests. Tell your provider if you take a high-dose biotin supplement before a draw.

Can I compare an immunoassay result with an LC/MS result?

Only roughly. Different methods and labs can give somewhat different numbers for the same sample. For trends, keep the method and the lab the same.

References

1. Rosner W, Auchus RJ, Azziz R, Sluss PM, Raff H. Utility, limitations, and pitfalls in measuring testosterone: an Endocrine Society position statement. J Clin Endocrinol Metab. 2007;92(2):405–413.
2. Centers for Disease Control and Prevention. Clinical Standardization Programs: Hormone Standardization (HoSt).
3. Labcorp. Testosterone, test 004226.
4. Travison TG, Vesper HW, Orwoll E, et al. Harmonized reference ranges for circulating testosterone levels in men of four cohort studies in the United States and Europe. J Clin Endocrinol Metab. 2017;102(4):1161–1173.
5. Bhasin S, Brito JP, Cunningham GR, et al. Testosterone therapy in men with hypogonadism: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2018;103(5):1715–1744.
6. U.S. Food and Drug Administration. Biotin interference with laboratory tests.