The Blood Tests Worth Asking For If You Are Tired All the Time
Persistent fatigue in a man over 45 has a findable cause more often than most people expect. The tests that find it are cheap, routine, and usually covered. Here is what to ask for and what each one is looking for.
Why bother
The default assumption — that tiredness after 45 is simply age — is sometimes right. But several conditions produce an identical experience, are common in this age group, and are straightforwardly treatable once identified. Assuming age costs you the years in between.
| Test | What it rules out | Why it matters here |
|---|---|---|
| TSH (thyroid) | Hypothyroidism | Produces fatigue, cold intolerance, weight gain and low mood. Common, and treated with a daily tablet. |
| Full blood count + ferritin | Anaemia, iron deficiency | Less common in men than women, which is exactly why it gets missed. In men it can also signal bleeding that needs investigating. |
| HbA1c / fasting glucose | Prediabetes, diabetes | Insulin resistance produces the post-meal energy crash pattern well before diagnosis. |
| Vitamin D (25-OH) | Deficiency | Analysis of U.S. survey data put deficiency at roughly 41% of adults.1 |
| Vitamin B12 | Deficiency | More common with age, with metformin use, and on plant-based diets. Causes fatigue and neurological symptoms. |
| Morning total & free testosterone | Hypogonadism | Must be drawn before 10 a.m. and confirmed on a second sample before anyone acts on it. |
| Liver and kidney panel | Organ dysfunction | Usually normal, but it is part of a sensible baseline and often bundled anyway. |
The one that is not a blood test
A sleep apnea screen. Obstructive sleep apnea affects an estimated 13% of men aged 30–70 at moderate-to-severe level and is frequently undiagnosed.2 No blood test finds it. If you snore habitually, wake unrefreshed, or a partner has noticed you stop breathing, ask specifically about a home sleep study — it is often the highest-value single test in this whole list.
How to ask
Doctors have limited appointment time and respond well to specificity. Something like: “I have had persistent fatigue for about six months. It has not improved with more sleep. I would like to rule out thyroid, anaemia, diabetes, vitamin D and B12, and I snore — can we consider a sleep study?”
Bring dates, not adjectives. When it started, whether it is constant or worse at particular times, what you have already tried. That is far more useful than “I am tired”.
Do not wait for an appointment if
Fatigue arrived suddenly, or comes with chest pain, breathlessness at rest, unexplained weight loss, blood in stool or urine, or fainting. Those warrant urgent medical attention, not a scheduled appointment and not a supplement.
And if everything comes back normal
That is a useful result, not a wasted appointment — it moves the question to sleep quality, training, alcohol, stress and diet, which is where most of the remaining answer usually sits. It also means that if you then choose to try a supplement, you are adding it on top of a known-clear baseline rather than using it to paper over something undiagnosed.
References
- Forrest KYZ, Stuhldreher WL. Prevalence and correlates of vitamin D deficiency in US adults. Nutrition Research. 2011;31(1):48–54.
- Peppard PE, Young T, Barnet JH, Palta M, Hagen EW, Hla KM. Increased prevalence of sleep-disordered breathing in adults. Am J Epidemiol. 2013;177(9):1006–1014.
Informational only; not medical advice. See our medical disclaimer.