Testosterone shows up on a blood test as one or more line items, typically labeled “Testosterone, Total” or “Testosterone, Free,” measured in nanograms per deciliter (ng/dL) in the United States. Depending on what your doctor ordered, you might see just one of these values or several, sometimes alongside related markers like sex hormone-binding globulin (SHBG). Here’s how to read what’s on your lab report.
The Three Types of Testosterone on a Lab Report
Your blood contains testosterone in different forms, and labs can measure them separately. Which ones appear on your report depends on what your provider ordered.
Total testosterone is the most commonly ordered test. It measures all the testosterone in your blood, both the portion attached to proteins and the portion floating freely. This is usually the first test ordered when checking hormone levels.
Free testosterone measures only the small fraction of testosterone that isn’t bound to any protein. This unattached testosterone is immediately available for your body to use for things like building muscle and maintaining bone density. Most of your testosterone is bound to proteins, particularly one called SHBG, which locks it up so your body can’t easily use it. Free testosterone typically makes up only about 2 to 3 percent of the total.
Bioavailable testosterone is a middle ground. It includes free testosterone plus testosterone loosely attached to a protein called albumin. Because albumin holds testosterone with about 100 times less grip than SHBG does, that portion can still break free and become usable. Bioavailable testosterone gives a fuller picture of what your body can actually work with.
Common Labels and Codes You’ll See
Lab reports often use shorthand that can look like gibberish. Here are the codes major laboratories use for testosterone-related tests:
- TTST: Testosterone, Total, Serum
- FRTST: Testosterone, Free, Serum
- TGRP: Testosterone, Total and Free panel
- TTBS: Testosterone, Total and Bioavailable, Serum
- SHBG1: Sex Hormone-Binding Globulin, Serum
Your lab may use slightly different abbreviations, but these are representative. If your provider ordered a broader hormone panel, you might also see LH (luteinizing hormone) and FSH (follicle-stimulating hormone) on the same report. These pituitary hormones help explain why testosterone might be low, since they’re the signals your brain sends to trigger testosterone production.
Units of Measurement
In the U.S., testosterone is reported in nanograms per deciliter (ng/dL). Labs in most other countries use nanomoles per liter (nmol/L), which is the international standard. The conversion factor is 0.0347, so if your result is 500 ng/dL, that equals about 17.4 nmol/L. Free testosterone is often reported in picograms per milliliter (pg/mL) because the amounts are so small.
If you’re comparing your results to reference ranges you’ve found online, make sure the units match. A number that looks alarming in one unit system may be perfectly normal in another.
Normal Ranges for Adults
For adult males (ages 18 and older), the general reference range for total testosterone is 193 to 824 ng/dL. For adult females, normal total testosterone is less than 40 ng/dL. These ranges can vary between laboratories because different facilities use different testing equipment and calibration methods. Your lab report will always include its own reference range printed right next to your result, and that’s the range your provider will use to interpret your numbers.
Keep in mind that testosterone levels naturally decline with age in men, so a 60-year-old near the lower end of the range isn’t in the same situation as a 25-year-old with the same number. Context matters, and a single value on paper doesn’t tell the whole story.
Why SHBG Often Appears Alongside Testosterone
If your lab report includes SHBG, it’s there for a reason. SHBG is the main protein that binds testosterone in your blood, and its level directly affects how much free testosterone you have. Two people can have identical total testosterone numbers but very different amounts of usable testosterone if their SHBG levels differ.
In many labs, free testosterone isn’t measured directly. Instead, the lab measures total testosterone and SHBG, then uses a formula to calculate free testosterone. If you see “calculated free testosterone” on your report, that’s what happened. Some labs do measure free testosterone directly using a technique called equilibrium dialysis, which is considered the gold standard but isn’t always available.
How the Lab Measures Testosterone
Two main methods exist, and which one was used can affect your results. Standard immunoassay testing is accurate at higher testosterone concentrations and works well for most adult men and for monitoring testosterone therapy. It’s also less expensive.
The more precise method, called tandem mass spectrometry, is better at measuring low testosterone levels accurately. This matters for children, most adult women, and anyone on testosterone-suppressing therapy. At low concentrations, immunoassay can produce unreliable results. If your provider suspects low testosterone, the mass spectrometry method gives a more trustworthy number. Your lab report may not specify which method was used, but your provider can find out.
Timing and Preparation
Testosterone follows a daily rhythm, peaking in the early morning and dropping throughout the day. For this reason, total testosterone blood draws are typically scheduled in the morning to capture your highest natural level. A test drawn at 3 p.m. could read meaningfully lower than one drawn at 8 a.m. in the same person, which could lead to a misleading result.
Some providers also recommend fasting before the test, though the primary concern is timing rather than food intake. If your first result comes back borderline low, most guidelines call for repeating the test on a separate morning before drawing any conclusions, since testosterone levels can fluctuate from day to day based on sleep, stress, illness, and other factors.