Blood Testing — What to Check and Why
Training and nutrition decisions are usually made blind — no idea what's actually happening with cholesterol, blood sugar, hormones, or inflammation until something goes wrong. Regular bloodwork replaces guessing with data. This guide covers which markers are actually worth tracking, how often, and the difference between a useful panel and an expensive way to manufacture anxiety. It's education, not diagnosis — a doctor interprets your results in the context of your full history; this page can't and doesn't try to.
Why It Matters
Most of what bloodwork catches has no symptoms until it's advanced — that's exactly why it's worth checking on a schedule rather than waiting to feel something.
🔍 Catching silent problems early
High cholesterol, rising blood sugar, and thyroid dysfunction typically produce no symptoms in their early stages — by the time you feel something, the condition is usually well established.
📈 Trends beat snapshots
A single result tells you where you are; repeated results on the same schedule tell you which direction you're heading — far more useful for catching a problem while it's still easy to reverse.
🎯 Personalising decisions with data
Low ferritin, borderline vitamin D, or a sluggish thyroid change what's actually worth fixing first — training and diet advice is generic until your own numbers narrow it down.
💪 Context for hormones and recovery
Persistent fatigue, stalled progress, or low libido have very different fixes depending on whether bloodwork points to low testosterone, thyroid dysfunction, or nothing hormonal at all — see the hormones guide and recovery guide for what those symptoms usually mean.
Types of Panels
More markers isn't automatically better — the right panel depends on what you're actually trying to answer.
Basic annual panel
★★★★★Lipids, fasting glucose/HbA1c, kidney and liver function, and a full blood count — widely available, usually covered by routine care, and catches the conditions that actually kill or disable most people.
Targeted panel
★★★★☆Hormones, vitamin D, iron studies, thyroid, and inflammation markers — genuinely useful when you have specific symptoms (fatigue, low libido, hair loss) or want to check something a basic panel doesn't cover.
100+ marker "wellness" panels
★★☆☆☆Expensive private panels testing dozens of markers with no clinical indication — statistically, testing enough things on a healthy person guarantees a few will land outside the "normal" range by chance alone, manufacturing anxiety over noise.
The Core Markers Worth Knowing
The handful of markers that show up in most useful panels, and why each one matters.
Lipid panel (incl. ApoB)
LDL and total cholesterol are the standard starting point, but ApoB — a direct count of the particles that actually drive arterial plaque — is a more precise cardiovascular risk marker where it's available.
Fasting glucose & HbA1c
HbA1c reflects average blood sugar over roughly the past three months — a far better early-warning marker for insulin resistance than a single fasting glucose reading, which can look normal even as things are trending the wrong way.
Vitamin D
Genuinely common to be deficient, especially with limited sun exposure — one of the few markers where supplementation on a confirmed deficiency has a clear, well-supported upside.
Ferritin & iron studies
Low ferritin causes fatigue and reduced training capacity well before it becomes diagnosable anaemia — worth checking directly rather than assuming tiredness is just poor sleep or overtraining.
Thyroid (TSH)
An underactive thyroid produces fatigue, weight gain, and low mood that mimic half the other things on this page — a single, cheap test that rules a common cause in or out.
hs-CRP (inflammation)
A general marker of systemic inflammation, linked to cardiovascular risk independent of cholesterol — useful as a broad signal, not specific enough on its own to diagnose anything.
Testosterone (free & total)
The starting point for investigating symptoms like low libido, fatigue, or stalled training progress — see the hormones guide for what to do with a low result before assuming it's the whole story.
The Blood Testing Stack
Ranked by impact — start at the top.
Tier S — Non-negotiable
An annual basic panel
✔Lipids, glucose/HbA1c, kidney and liver function, full blood count — the highest-value, lowest-cost thing on this page, and the foundation everything else builds on.
Track trends, not single points
✔Keep every result on the same schedule (same time of year, similar fasting conditions) so you're comparing like with like — a slow upward trend across three years is far more actionable than any single reading.
Follow the fasting instructions
✔Glucose and lipid results shift meaningfully if you eat beforehand when fasting was required — a result taken under the wrong conditions isn't comparable to your other readings and can look falsely alarming.
Discuss results with a doctor
✔Reference ranges are population averages, not individual verdicts — a clinician interprets a result against your history, symptoms, and other markers together, which no lab printout or article can do for you.
Tier A — Strong case
Retest before reacting
✔A single out-of-range value is often lab variation or a one-off fluke — confirming with a second test before changing diet, supplements, or medication avoids chasing noise.
Symptom-driven targeted panels
✔Persistent fatigue, hair loss, or low libido are worth investigating with the specific relevant panel (thyroid, ferritin, testosterone) rather than either ignoring it or ordering everything available.
Test around a significant change
✔A before/after panel around a major diet change, a new supplement, or a body-composition shift tells you whether it actually moved anything measurable, instead of relying on how you feel.
Tier B — Situational
At-home finger-prick panels
~Convenient for tracking a marker you already know is relevant, but generally less accurate than a venous draw — fine for casual trend-watching, not the panel to base a real medical decision on.
DEXA and physiological testing
~Body composition and fitness-capacity testing complements bloodwork but measures a different thing entirely — see the progress tracking guide for where these fit alongside scale weight and photos.
Tier C — Skip it
Chasing every marker on a 100+ panel
✘Testing enough markers on a healthy person statistically guarantees a few will land outside "normal" by chance — reacting to each one individually creates anxiety and unnecessary follow-up testing with no real health benefit.
Self-diagnosing from a single result
✘Deciding you have a specific condition from one lab value, without clinical context or a retest, routinely leads to the wrong conclusion — bloodwork narrows down what to ask a doctor about, it doesn't replace asking.
Ignoring a clearly abnormal result
✘"I feel fine" isn't evidence against a result that's clearly and repeatedly outside range — the whole point of testing is that the conditions it catches often have no symptoms until they're advanced.
Myths, Debunked
Myth: "More markers always means more insight."
Reality: Past a certain point, extra markers mostly add statistical noise — testing enough things on a healthy person guarantees a few "abnormal" results by chance alone.
Myth: "One abnormal result means something is wrong."
Reality: Lab variation, hydration, recent food, and even the time of day can shift a single result — a repeat test on the same conditions is what confirms whether it's real.
Myth: "You need to fast for every blood test."
Reality: Fasting mainly matters for glucose and lipids — many other markers (thyroid, vitamin D, ferritin) aren't meaningfully affected by recent food, though it's still worth following whatever the lab specifies.
Myth: "An annual panel gives you the full picture."
Reality: Bloodwork is one input alongside symptoms, family history, and physical findings — a clean panel doesn't rule out everything, it rules out what that specific panel actually tests for.