Testing for low testosterone requires a simple blood draw, but the timing, preparation, and type of test all matter. A total testosterone level below 300 ng/dL on two separate morning blood tests, combined with symptoms, is the standard threshold for diagnosis. Getting an accurate result is straightforward if you know what to do before and during the process.
Why Timing and Fasting Matter
Testosterone levels follow a daily rhythm, peaking in the early morning and dropping as the day goes on. For men under 45, the difference is dramatic: levels drawn after 9 a.m. can be 150 to 200 ng/dL lower than those drawn between 7 and 9 a.m. That’s enough to push a normal result into the “low” range, or vice versa. Men over 45 show less variation throughout the day, but morning draws are still the standard recommendation.
Eating also temporarily tanks your testosterone. After a meal, total testosterone drops by an average of 100 to 123 ng/dL, bottoming out around 60 minutes after eating. In one study, 56% of healthy men with normal testosterone dipped below 300 ng/dL after eating a mixed meal. The effect can last over two hours. This is why guidelines specify a fasting blood draw, ideally before you’ve eaten anything that morning.
The ideal test setup: schedule your blood draw between 7 and 9 a.m., skip breakfast, and drink only water beforehand.
What Blood Tests Are Ordered
The first test is almost always total testosterone, which measures both the testosterone bound to proteins in your blood and the small amount floating freely. For most men, this single number is enough to determine whether levels are low.
If your total testosterone lands in a borderline zone (roughly 200 to 400 ng/dL), or if you have a condition that affects the proteins testosterone binds to, your doctor will likely order a free testosterone test as well. Free testosterone measures only the unbound portion that your body can actually use. Conditions like obesity, type 2 diabetes, liver disease, and aging can all shift the ratio between bound and free testosterone, making the total number misleading. Bioavailable testosterone, which includes both free testosterone and the loosely bound portion, is considered the most informative follow-up test in these situations.
If your testosterone comes back low, the next step is testing two hormones produced by the pituitary gland: LH and FSH. These help pinpoint where the problem originates. High LH and FSH alongside low testosterone means the testes themselves aren’t producing enough, a pattern called primary hypogonadism. Low or normal LH and FSH with low testosterone points to a signaling problem in the brain, called secondary hypogonadism. This distinction matters because the causes and treatments differ significantly. Very low testosterone (below 150 ng/dL) with signs of secondary hypogonadism may prompt your doctor to order brain imaging to check for a pituitary issue.
You Need Two Low Results, Not One
A single low reading isn’t enough for a diagnosis. The American Urological Association’s guidelines are clear: the diagnosis of low testosterone requires two total testosterone measurements taken on separate occasions, both drawn in the early morning, ideally at the same lab using the same testing method. Testosterone levels naturally fluctuate from day to day, and a bad night of sleep, a stressful week, or a recent illness can all temporarily suppress levels. Two consistent results rule out a one-off dip.
Symptoms That Prompt Testing
Low testosterone is never diagnosed on blood work alone. You need both low levels and symptoms. The most reliable red flag is reduced sex drive, which outperforms any formal screening questionnaire as a predictor of low testosterone. Other common symptoms include erectile difficulty, persistent fatigue, loss of muscle mass or strength, increased body fat (particularly around the midsection), depressed mood, difficulty concentrating, and reduced motivation.
Several of these symptoms overlap with other conditions. Sleep apnea, for example, causes fatigue, low energy, reduced sex drive, and erectile problems, and it independently lowers testosterone by disrupting deep sleep. Thyroid disorders, depression, and poorly managed diabetes can all produce a similar picture. A good evaluation doesn’t stop at testosterone. If your levels come back normal but symptoms persist, these other causes are worth investigating.
What About At-Home Test Kits
At-home testosterone kits have become widely available, typically using either a finger-prick blood spot or a saliva sample. They can be a reasonable first screening step, but they come with significant accuracy limitations. Finger-prick samples show three to eight times more variability in results compared to a standard blood draw from a vein. Smaller sample volumes, contamination during collection, and damage to blood cells all contribute to this inconsistency.
If an at-home kit flags low testosterone, treat it as a prompt to get a proper venous blood draw at a lab, not as a diagnosis. And the same rules apply to at-home kits: test in the early morning while fasting for the most reliable reading.
What “Normal” Actually Looks Like
The 300 ng/dL cutoff used for diagnosis is a clinical threshold, not a biological cliff. The normal range for healthy young men spans roughly 264 to 916 ng/dL, with testosterone peaking around age 19 and settling to a slightly lower average by age 40. After 40, average levels hold relatively steady for most men, though the range of what’s normal widens considerably with age. A 50-year-old with a level of 350 ng/dL and no symptoms isn’t deficient, while a 30-year-old at 280 ng/dL with significant fatigue, low libido, and mood changes likely is.
The widely cited claim that testosterone inevitably declines with age is more nuanced than it sounds. Population-level drops in older men are largely driven by increasing rates of obesity, sleep apnea, and chronic illness, all of which suppress testosterone. Healthy, non-obese older men often maintain levels comparable to younger men. This means that if your levels are low, the cause is worth investigating rather than simply attributing it to aging.
Getting Tested: The Practical Steps
You can request testosterone testing through your primary care doctor, a urologist, or an endocrinologist. Most insurance plans cover the blood work when symptoms are present. Here’s what the process typically looks like:
- First visit: Discuss your symptoms. Your doctor orders a fasting morning total testosterone test.
- First blood draw: Arrive at the lab between 7 and 9 a.m. without eating. A standard blood draw from your arm takes a few minutes.
- If results are low: A second fasting morning test is scheduled on a different day to confirm. Free testosterone, LH, and FSH are often added to this round.
- If both results are below 300 ng/dL with symptoms: Your doctor discusses the underlying cause and treatment options.
The entire diagnostic process, from first appointment to confirmed diagnosis, typically takes two to four weeks depending on scheduling and lab turnaround times.