Last updated: August 24, 2026
A testosterone blood test measures the concentration of testosterone in blood and is commonly used when evaluating suspected testosterone deficiency, androgen excess, reproductive disorders, infertility, delayed or early puberty, and selected pituitary or testicular conditions.
Interpreting testosterone is more complicated than simply deciding whether a number is inside or outside a laboratory reference interval. Testosterone concentrations vary with time of day, age, health status, medications, sex hormone-binding globulin (SHBG), laboratory method, and other physiological factors.
This laboratory-focused guide explains total testosterone, free testosterone, normal testosterone ranges, low and high testosterone, SHBG, specimen collection, analytical methods, potential interferences, and laboratory interpretation.
Medical disclaimer: This article is intended for laboratory and educational purposes and does not provide a diagnosis or individualized treatment advice. Testosterone results should be interpreted using the reference interval supplied by the testing laboratory and in the context of symptoms, clinical history, medications, age, sex, and other laboratory findings.
1. What Is Testosterone?
Because testosterone participates in bone physiology, related endocrine assessment may sometimes include Vitamin D blood testing when clinically appropriate.
Testosterone is a steroid hormone belonging to the androgen group. In males, most circulating testosterone is produced by Leydig cells in the testes under stimulation from luteinizing hormone (LH). Smaller quantities of androgens are produced by the adrenal glands.
Females also produce testosterone, although circulating concentrations are normally substantially lower. Testosterone and its related androgens participate in reproductive function, sexual development, bone metabolism, muscle mass, erythropoiesis (see Complete Blood Count (CBC) and anemia laboratory diagnosis), libido, and other physiological processes.
Testosterone production is regulated through the hypothalamic-pituitary-gonadal (HPG) axis. Gonadotropin-releasing hormone (GnRH) stimulates pituitary secretion of LH and FSH. LH stimulates testicular testosterone production, while testosterone participates in negative-feedback regulation of this axis.
2. What Is a Testosterone Blood Test?
A testosterone blood test measures testosterone in a serum or plasma sample, depending on the laboratory method and manufacturer specifications.
Testing may include:
- Total testosterone
- Free testosterone
- Calculated free testosterone
- Bioavailable testosterone
- Testosterone interpreted together with SHBG and albumin
Total testosterone is generally the initial and most commonly requested testosterone measurement. Free testosterone may provide additional information in selected patients, particularly when total testosterone is borderline or SHBG concentrations are abnormal.
3. Why Is Testosterone Tested?
A clinician may request testosterone testing during evaluation of:
- Symptoms or signs suggesting testosterone deficiency
- Reduced libido
- Erectile dysfunction in an appropriate clinical setting
- Male infertility
- Reduced secondary sexual characteristics
- Suspected testicular dysfunction
- Suspected pituitary or hypothalamic disease
- Delayed or precocious puberty
- Androgen excess in females
- Hirsutism or virilization
- Selected menstrual or reproductive disorders
- Monitoring in specific clinical situations under medical supervision
A testosterone result by itself does not establish the cause of an abnormal concentration. Additional hormonal testing is frequently necessary.
4. What Is Total Testosterone?
Total testosterone represents testosterone circulating in several forms, including testosterone bound to SHBG, testosterone weakly bound to albumin, and the small unbound or free fraction.
Because most circulating testosterone is protein-bound, total testosterone is substantially higher than the free testosterone concentration.
Laboratory point: Total testosterone is usually the first biochemical measurement used when testosterone deficiency is suspected in men. Interpretation should account for collection time, repeat testing when appropriate, symptoms, SHBG status, assay method, and the laboratory's reference interval.
5. What Is Free Testosterone?
Free testosterone refers to the fraction of circulating testosterone that is not bound to SHBG or albumin.
It represents only a small proportion of total circulating testosterone, but it can be clinically useful when total testosterone does not adequately reflect androgen status because of abnormal SHBG concentrations.
Free testosterone may be:
- Measured using equilibrium dialysis in specialized laboratories
- Estimated using validated calculations based on total testosterone, SHBG, and sometimes albumin
- Measured by some direct commercial assays, although analytical performance differs among methods
The testing method matters substantially. Free testosterone results obtained by different analytical techniques should not automatically be considered interchangeable.
6. What Is Bioavailable Testosterone?
Bioavailable testosterone generally includes free testosterone plus testosterone that is weakly bound to albumin. It excludes the testosterone strongly bound to SHBG.
Bioavailable testosterone testing is less commonly used than total testosterone and may be available only in selected laboratories.
7. Total vs Free Testosterone
| Feature Total Testosterone Free Testosterone | ||
|---|---|---|
| What it represents | Bound + unbound testosterone | Unbound testosterone |
| Common initial test | Yes | Usually no |
| Influenced by SHBG | Yes | Interpretation can help when SHBG is abnormal |
| Availability | Widely available | Method-dependent |
| Typical role | Initial biochemical assessment | Selected borderline or altered-SHBG situations |
8. SHBG and Testosterone Interpretation
Sex hormone-binding globulin (SHBG) is an important testosterone-binding protein. Changes in SHBG can alter total testosterone without producing an equivalent change in biologically available testosterone.
Conditions associated with altered SHBG may therefore complicate interpretation.
When SHBG is increased
Total testosterone can appear relatively higher because more testosterone is protein-bound. Depending on the clinical situation, assessment of free testosterone may provide additional information.
When SHBG is decreased
Total testosterone can appear lower even when free testosterone is not reduced to the same degree.
For this reason, SHBG measurement can be useful when total testosterone is borderline or when a condition known to alter SHBG is present.
9. Testosterone Normal Range
There is no single universal testosterone reference interval appropriate for every laboratory, patient population, sex, age group, and analytical method.
Reference intervals depend on factors including:
- Age
- Sex
- Population used to establish the interval
- Collection time
- Assay methodology
- Calibration and standardization
- Laboratory-specific validation
Important: Always interpret the patient's result against the reference interval printed on the laboratory report. A general internet reference range should never replace the laboratory-specific interval.
Common adult male context
Many laboratories report adult male total testosterone in ng/dL or nmol/L. Reference limits vary considerably between laboratories.
In clinical guidelines for male testosterone deficiency, values around 300 ng/dL are commonly discussed as a decision threshold, but this should not be treated as a universal laboratory reference limit or as a diagnosis by itself.
Diagnosis of male hypogonadism requires appropriate clinical findings together with consistently low testosterone measurements obtained under appropriate conditions.
Females
Female testosterone concentrations are much lower than typical adult male concentrations. Because concentrations are low, analytical sensitivity and specificity become especially important.
The laboratory's age-, sex-, and method-specific reference interval should be used.
10. Testosterone Units and Conversion
Total testosterone is commonly reported as:
- ng/dL
- ng/mL
- nmol/L
A commonly used approximate conversion is:
Testosterone (nmol/L) ≈ Testosterone (ng/dL) × 0.0347
Testosterone (ng/dL) ≈ Testosterone (nmol/L) × 28.8
Free testosterone may be reported in pg/mL, ng/dL, pmol/L, or other units depending on the laboratory.
Always verify units before comparing a result with a reference interval.
11. Why Is Testosterone Usually Tested in the Morning?
Testosterone shows biological variation throughout the day. In many men, concentrations are higher earlier in the day and lower later.
For evaluation of suspected testosterone deficiency, major endocrine guidelines recommend appropriately timed morning measurements, with repeat testing when an initially low concentration requires confirmation.
Timing can be more complicated in shift workers because the testosterone rhythm is related to sleep patterns as well as conventional clock time.
12. How to Prepare for a Testosterone Blood Test
Preparation requirements should follow the clinician's instructions and the testing laboratory's protocol.
Important pre-analytical considerations may include:
- Collection at the recommended time
- Fasting when requested for diagnostic evaluation
- Avoiding testing during significant acute illness when clinically appropriate
- Recording medications and supplements
- Documenting testosterone or androgen therapy if applicable
- Considering sleep schedule in shift workers
Patients should not stop prescription medicines or hormone therapy unless instructed by their healthcare professional.
13. Specimen Collection and Handling
Testosterone is commonly measured in serum, although specimen requirements depend on the analytical platform.
Laboratory personnel should verify:
- Correct patient identification
- Correct specimen type
- Collection time when clinically relevant
- Appropriate tube
- Sample integrity
- Required centrifugation and separation
- Storage stability
- Analyzer-specific specimen requirements
Gross hemolysis, lipemia, icterus, insufficient sample volume, or other specimen problems should be managed according to the laboratory's validated acceptance and rejection criteria.
14. How Is Testosterone Measured in the Laboratory?
Testosterone can be measured using several analytical technologies. Two major categories are immunoassays and mass-spectrometry-based methods.
Immunoassays
Automated immunoassays are widely available and provide rapid testing suitable for routine laboratory workflows.
Performance can vary by platform, particularly at low testosterone concentrations. Cross-reactivity, calibration differences, matrix effects, and analytical interference can affect results.
LC-MS/MS
Liquid chromatography-tandem mass spectrometry (LC-MS/MS) provides high analytical specificity and is widely regarded as an important reference-level approach for steroid hormone measurement when properly validated.
It is particularly valuable when accurate measurement at low concentrations is important, although availability differs between laboratories.
Free testosterone measurement
Equilibrium dialysis is considered a reference approach for free testosterone assessment. Alternatively, calculated free testosterone may be derived from total testosterone and SHBG using an appropriate validated equation.
15. What Does Low Testosterone Mean?
A low testosterone result means that the measured concentration is below the applicable reference or clinical decision threshold, but the laboratory result alone does not establish hypogonadism.
Testosterone concentrations can vary from day to day and can be influenced by collection timing, food intake, sleep, acute illness, medications, obesity, metabolic status (see HbA1c and Blood Glucose Test), SHBG, and laboratory method.
In adult men, professional guidelines emphasize that testosterone deficiency should be diagnosed only when compatible symptoms or signs occur together with consistently low testosterone concentrations.
16. Causes of Low Testosterone
Possible causes or associations include:
- Primary testicular dysfunction
- Pituitary disease
- Hypothalamic disorders
- Hyperprolactinemia
- Certain genetic disorders; selected endocrine workups may also include ferritin assessment when iron overload is clinically suspected
- Testicular injury
- Some chemotherapy or radiation exposure
- Certain medications
- Severe systemic illness
- Obesity and metabolic conditions in selected patients
- Age-related physiological changes
The cause cannot usually be identified from testosterone alone. LH, FSH and other laboratory investigations help determine where dysfunction may be occurring.
17. Primary vs Secondary Hypogonadism
Once testosterone deficiency has been appropriately established, LH and FSH are important for differentiating primary testicular dysfunction from central hypothalamic-pituitary dysfunction.
| Pattern Testosterone LH/FSH Possible Interpretation | |||
|---|---|---|---|
| Pattern 1 | Low | Elevated | Suggests primary testicular dysfunction |
| Pattern 2 | Low | Low or inappropriately normal | Suggests secondary/central hypogonadism |
These are simplified biochemical patterns and are not substitutes for full clinical assessment.
18. What Does High Testosterone Mean?
A testosterone concentration above the applicable reference interval should first be interpreted according to sex, age, medications, supplements, treatment history, clinical presentation, and assay method.
An unexpectedly high result may warrant confirmation or additional testing, especially when the biochemical result is inconsistent with the clinical picture.
19. Causes of High Testosterone
Potential causes or associations can include:
- Exogenous testosterone use
- Androgen-containing medications or supplements
- Selected adrenal disorders
- Selected testicular disorders
- Androgen-producing tumors
- Polycystic ovary syndrome in women
- Congenital adrenal hyperplasia
- Changes in SHBG affecting total testosterone
- Analytical interference
The differential diagnosis differs substantially between males, females, children, and patients receiving hormonal therapy.
20. Testosterone Blood Testing in Women
Testosterone testing in women is commonly performed when clinical features suggest androgen excess.
Possible indications include:
- Hirsutism
- Virilization
- Acne in an appropriate endocrine context
- Menstrual abnormalities
- Suspected polycystic ovary syndrome
- Suspected adrenal or ovarian androgen excess
Because female testosterone concentrations are relatively low, assay performance at low concentrations is particularly important.
21. Testosterone and Male Fertility
Testosterone is essential for normal male reproductive physiology, but serum testosterone does not directly measure fertility.
Male infertility assessment may require additional investigations such as:
- Semen analysis
- FSH
- LH
- Prolactin
- Other endocrine testing depending on clinical findings
Importantly, exogenous testosterone can suppress gonadotropin secretion and spermatogenesis. Testosterone therapy should therefore not be viewed as a general fertility treatment.
22. Laboratory Tests Commonly Ordered with Testosterone
| Test Why It May Be Useful | |
|---|---|
| LH | Helps distinguish primary from central hypogonadism |
| FSH | Provides information about gonadal axis and spermatogenesis |
| SHBG | Helps interpret total testosterone when binding is altered |
| Albumin | May be used in calculated free testosterone equations |
| Prolactin | Useful in selected cases of secondary hypogonadism |
| Estradiol | Useful in selected endocrine or reproductive evaluations |
| TSH | May identify thyroid dysfunction contributing to symptoms |
| Iron studies | May be considered in selected central hypogonadism evaluations |
23. Laboratory Interferences and Sources of Error
Unexpected testosterone results should be assessed for both biological and analytical causes.
Pre-analytical factors
- Collection at an inappropriate time
- Recent food intake when fasting collection is required
- Acute illness; where endocrine stress evaluation is relevant, see Cortisol Blood Test
- Sleep disruption
- Medication or supplement effects
- Incorrect specimen handling
Analytical factors
- Assay-specific cross-reactivity
- Calibration differences
- Method-to-method bias
- Heterophile antibody interference in susceptible immunoassays
- Biotin-related interference in susceptible assay designs
- Reduced accuracy at very low concentrations with some methods
Laboratory approach: When a testosterone result is strongly inconsistent with the clinical picture, consider specimen verification, repeat measurement, review of medications and supplements, assessment for analytical interference, and confirmation using an alternative or more specific method when clinically justified.
24. Step-by-Step Laboratory Interpretation
Step 1: Verify the patient and specimen
Confirm patient identification, specimen type, collection time, sample quality, and relevant pre-analytical information.
Step 2: Check units and reference interval
Do not compare results from different laboratories without checking units, analytical methods, and reference intervals.
Step 3: Determine whether the result is total or free testosterone
Total and free testosterone represent different measurements and should not be interpreted using the same reference interval.
Step 4: Consider timing
For suspected male testosterone deficiency, determine whether collection was performed under appropriate morning conditions.
Step 5: Consider repeat testing
An isolated low testosterone concentration is generally insufficient to establish testosterone deficiency. Guidelines recommend confirmation with another appropriately collected measurement.
Step 6: Assess SHBG when appropriate
If total testosterone is borderline or the patient has a condition likely to alter SHBG, SHBG and free testosterone assessment may improve interpretation.
Step 7: Evaluate LH and FSH
When biochemical testosterone deficiency has been established, gonadotropins help distinguish primary testicular dysfunction from hypothalamic-pituitary dysfunction.
Step 8: Correlate clinically
Laboratory findings should be interpreted together with symptoms, examination findings, medical history, medication exposure, and other investigations.
25. Example Testosterone Interpretation Patterns
| Total Testosterone SHBG LH/FSH Possible Laboratory Consideration | |||
|---|---|---|---|
| Low | Normal | High | Consider primary gonadal dysfunction |
| Low | Normal | Low/normal | Consider central hypothalamic-pituitary dysfunction |
| Low | Low | Variable | Total testosterone may underestimate androgen status; assess clinical context and free testosterone when indicated |
| Normal/high | High | Variable | Higher SHBG may increase measured total testosterone |
| Unexpectedly high | Variable | Variable | Review therapy, supplements, clinical context and possible assay interference |
26. Can One Low Testosterone Result Diagnose Low Testosterone?
Usually, no.
Testosterone has significant biological and day-to-day variability. Major clinical guidelines recommend confirming an initially low result using another appropriately timed measurement before establishing biochemical testosterone deficiency.
Symptoms and signs must also be considered. A laboratory number alone is not equivalent to a diagnosis of hypogonadism.
27. Testosterone, Age, and Reference Intervals
Testosterone concentrations and their interpretation can change with age. However, age alone should not be used to diagnose testosterone deficiency.
Clinical interpretation should use an appropriate reference interval and account for symptoms, repeat testing, health status, SHBG, medications, and analytical methodology.
28. Quality Control in Testosterone Testing
Reliable testosterone measurement requires robust laboratory quality systems.
Important elements include:
- Internal quality control (IQC)
- Calibration verification
- External quality assessment or proficiency testing; see also Laboratory Quality Indicators
- Method validation or verification
- Precision assessment
- Bias assessment
- Reference interval verification
- Lot-to-lot monitoring
- Instrument maintenance
- Documented corrective actions when QC fails
Laboratories should not release patient results from an analytical run that fails established QC acceptance criteria until the problem has been appropriately investigated and resolved according to laboratory procedure.
29. Why Testosterone Results Differ Between Laboratories
Two laboratories may occasionally produce different testosterone values because of:
- Different analytical platforms
- Different calibration systems
- Immunoassay versus LC-MS/MS methodology
- Different reference populations
- Different reference intervals
- Pre-analytical differences
- Biological variation between collection times
Serial monitoring is often easier to interpret when testing is performed under similar collection conditions and, when possible, using the same laboratory and analytical method.
30. Key Laboratory Takeaways
- Total testosterone is generally the initial testosterone test.
- Free testosterone can be useful when total testosterone is borderline or SHBG is abnormal.
- Morning collection is important when evaluating suspected testosterone deficiency in men.
- An isolated low result should generally be confirmed.
- Use the laboratory-specific reference interval.
- SHBG can substantially influence total testosterone interpretation.
- LH and FSH help distinguish primary from secondary hypogonadism.
- Assay methodology matters, particularly at low testosterone concentrations.
- Unexpected results should prompt review of pre-analytical and analytical factors.
- Laboratory results must be interpreted together with clinical findings.
31. Frequently Asked Questions
What is a testosterone blood test?
It is a laboratory test that measures testosterone concentration in blood. Total testosterone is the most commonly requested initial measurement.
What is the normal testosterone range?
There is no universal range suitable for every laboratory. Normal intervals vary according to age, sex, assay method, reference population, and laboratory. Use the interval printed on the laboratory report.
What is the difference between total and free testosterone?
Total testosterone includes both protein-bound and unbound testosterone. Free testosterone represents the small fraction that is not bound to circulating proteins.
Is 300 ng/dL low testosterone?
Approximately 300 ng/dL is used as a clinical decision threshold in some professional guidelines for adult men, but a single value does not diagnose testosterone deficiency. Symptoms, repeat morning testing, assay method, and clinical context must also be considered.
What time should testosterone be tested?
For evaluation of suspected testosterone deficiency in men, appropriately timed morning testing is generally recommended. Individual circumstances such as shift work can affect interpretation.
Do I need to repeat a low testosterone result?
Guidelines generally recommend confirmation of an initially low testosterone concentration with a second appropriately collected measurement.
Why is SHBG tested with testosterone?
SHBG affects the amount of testosterone circulating in bound form. Abnormally high or low SHBG can make total testosterone more difficult to interpret.
Can testosterone be low during illness?
Yes. Acute illness and other physiological stresses can temporarily influence testosterone concentrations, which is one reason clinical context and appropriate timing are important.
Which method is best for testosterone testing?
The appropriate method depends on the clinical setting and concentration range. Well-validated LC-MS/MS methods offer high analytical specificity, while automated immunoassays remain widely used for routine testing.
Can a testosterone test diagnose infertility?
No. Testosterone is only one part of male reproductive assessment. Semen analysis and additional hormonal investigations may be necessary.
32. Authoritative References
- MedlinePlus — Testosterone Levels Test
- Endocrine Society — Testosterone Therapy for Hypogonadism Guideline
- American Urological Association — Testosterone Deficiency Guideline
- CDC — Hormone Standardization Program: Testosterone
- PubMed — Testosterone Therapy in Men With Hypogonadism: Endocrine Society Clinical Practice Guideline
Medical Disclaimer: MedLab Academy provides educational information for laboratory professionals, students, and readers interested in laboratory medicine. The information on this page is not intended to replace professional medical evaluation, diagnosis, or treatment. Reference ranges and clinical decision limits vary by laboratory, analytical method, age, sex, and clinical context.