Tiredness that doesn't lift with sleep is one of the most common reasons people test, and honestly one of the most satisfying. A short list of causes covers most cases, and every one of them is fixable.

It Usually Has a Findable Cause

Iron is first, especially in women, and it empties in stages. Stores go first, haemoglobin later. That's why ferritin can be on the floor while a routine blood count reads completely normal, and why testing only the blood count misses it.

Then thyroid. Then vitamin D and B12, both everywhere, both producing exactly this. And undiagnosed diabetes turns up as plain tiredness more often than people expect. None of these can be found by an examination, and none of them respond to sleeping more, which is usually what's been tried already.

Who Should Consider These Tests

• You're tired after seven or more hours of sleep

• You're winded on stairs you used to manage

• Brain fog, can't hold concentration

• Hair fall, dry skin, always cold

• You're vegetarian or eat restrictively

• Your energy noticeably dropped over recent months

What Each Test Tells You

This page lists 8 options. Here's what each one actually measures, so you can pick instead of guessing.

Blood tests

• Diabetes Testing (FBS + PLBS): Sugar before food and two hours after. The second number is the interesting one, because that's where trouble shows up first.

• TSH Test: Just the brain's signal to the thyroid. It moves before anything else does, so it's the cheaper first look if you only want one number.

• Serum Iron Test: Iron circulating right now, as opposed to what's in storage. Read it next to ferritin, never on its own.

• Complete Blood Picture (CBP): Counts your red cells, white cells and platelets. It's the cheapest way to catch anaemia or an infection you didn't know you had, and it's the single most booked test we do.

• Thyroid Function Tests: Checks the hormones that set how fast your body runs. Worth doing if you're tired, gaining or losing weight without trying, or your hair's thinning.

• Ferritin Test: This is your iron savings account, and it empties before your blood count changes. That's why you can feel exhausted while a routine CBP looks perfectly fine.

• Vitamin B12 Test: Your nerves and red blood cells need B12. If you're vegetarian, you're at real risk, and the symptoms are easy to miss: tingling hands, fuzzy thinking, no energy.

• Vitamin D (25 - Hydroxy Vitamin D, Serum): Your body makes this from sunlight, and most people who work indoors don't get enough. Low levels show up as aching bones, weak muscles and flat mood.

How to Prepare

• No fasting: Complete Blood Picture (CBP), TSH Test, Vitamin D (25 - Hydroxy Vitamin D, Serum)

• 8 to 12 hours fasting for the first sample: Diabetes Testing (FBS + PLBS)

• Morning sample is better: Ferritin Test

• Morning, after an overnight fast: Serum Iron Test

• No fasting. Take your thyroid tablet after the sample, not before: Thyroid Function Tests

• No fasting. Ask your doctor before pausing supplements: Vitamin B12 Test

Tell the collection team everything you're taking, prescription or not. Plenty of supplements move these numbers, and without that context your report reads wrong.

How Often to Repeat

Test when it's persistent rather than waiting it out. Retest eight to twelve weeks after starting any treatment to check it's actually working.

Understanding Your Results

If everything comes back clean, that's genuinely useful rather than a dead end. It rules out the medical causes and moves the conversation to sleep quality, stress and mental health, which are treatable in their own right.

These tests point at a diagnosis. They don't make one. Read your report with a doctor who knows your history and what you're currently taking.