Being tired all the time is one of the most common reasons people come in, and one of the most frequently dismissed. You mention it, you get told your labs look fine, and you leave with the impression that this is just what your thirties or forties or fifties feel like.
It usually is not. Persistent fatigue almost always has a cause, and a standard panel is not designed to find most of them.
Here are five worth ruling out.
- Thyroid function beyond TSH
Most annual physicals check TSH alone. TSH is a signal from the pituitary, not a measurement of the hormone your cells actually use. Someone can have a TSH inside the reference range while free T3 sits at the bottom of its own range or conversion from T4 to T3 is impaired.
What to test: TSH, free T4, free T3, reverse T3, and thyroid antibodies. The antibodies matter because autoimmune thyroid disease often shows up in antibody levels years before the other numbers move.
- Iron and ferritin, not just hemoglobin
You can be low on iron long before you are anemic. Hemoglobin is the last number to fall, which means a normal complete blood count does not rule out iron deficiency. Ferritin measures stored iron, and low stores cause fatigue on their own.
This is especially common in menstruating women and in anyone who does a lot of endurance exercise.
- B12 and vitamin D
The reference range for B12 is wide, and people at the low end of normal often feel noticeably better once it comes up. Absorption is the other issue: certain medications, including common acid reducers and metformin, interfere with B12 uptake over time.
Vitamin D is worth checking in Las Vegas despite the sunshine, because most people spend the hottest months indoors and use sun protection when they are outside.
- Hormones, in both men and women
Fatigue is one of the first symptoms of hormonal change and one of the last things tested. In women, perimenopause can begin in the late thirties and often shows up as exhaustion and disrupted sleep before cycles change noticeably. In men, testosterone declines gradually enough that the fatigue gets attributed to age, work, or stress.
Cortisol matters here too. Chronic stress alters the pattern of cortisol across the day, which affects how you sleep and how you feel when you wake up.
- Blood sugar swings
A normal fasting glucose does not rule out metabolic dysfunction. Insulin rises years before glucose does, so fasting insulin and hemoglobin A1c together give a much earlier picture. If your energy crashes in the mid-afternoon or you feel shaky between meals, this is worth ruling out.
What else deserves attention
Sleep quality, not just hours. Sleep apnea is significantly underdiagnosed, especially in women, and it produces exactly this kind of fatigue.
Medication side effects. Several common prescriptions cause fatigue and it is worth reviewing the list you are on.
And it is worth saying plainly: persistent low energy can also be depression, and that deserves real treatment rather than a supplement.
Why standard labs miss this
A standard panel is designed to detect disease. Reference ranges come from the general population, which means a result can be technically normal and still be far from optimal for you. Functional medicine testing looks at a wider set of markers and interprets them against how you actually feel rather than only against the range.
What we do with the results
Once the cause is identified, treatment follows the finding. That might mean hormone optimization, correcting a deficiency through nutrition and targeted supplementation, IV therapy for faster repletion in some cases, or addressing the metabolic pattern driving the crashes. What it should never mean is guessing.
If you have been told your labs are normal and you still feel exhausted, that gap is worth investigating. Call (702) 465-7471 or book a consultation.