Blood Work for Men Over 40: What to Test, What the Numbers Mean

You cannot fix what you do not measure. Every article on this site — the CRON meal plan, the zinc and magnesium protocol, the case against premature TRT — is built on the premise that fixing inputs fixes outputs. Blood work is how you verify that premise. An annual panel costs less than two months of most supplements and tells you more than any symptom tracker ever will.

The Panel to Request

A standard metabolic panel from your doctor covers maybe half of what matters. The rest you need to ask for by name. Here is the full list, organized by system.

Hormones

• Total testosterone. The headline number. Measures all testosterone in the blood, including the fraction bound to SHBG and albumin. Necessary but insufficient on its own.
• Free testosterone. The unbound fraction — roughly 2-3% of total — that is biologically active. You can have a total testosterone of 600 ng/dL and still be symptomatic if SHBG is binding most of it.
• SHBG (sex hormone-binding globulin). The carrier protein that binds testosterone and makes it unavailable. SHBG rises with age, increasing approximately 1.6% per year after 40. High SHBG with normal total T produces the same symptoms as low total T.
• Estradiol (E2). The primary estrogen in men. Aromatase converts testosterone to estradiol, and the ratio matters. Elevated estradiol relative to testosterone correlates with increased visceral fat and reduced libido in men.

Metabolic

• Fasting glucose. A snapshot of blood sugar regulation at a single point. Easy to game with a day of clean eating, which is why it is paired with HbA1c.
• HbA1c (glycated hemoglobin). A 90-day average of blood glucose. Cannot be gamed. A meta-analysis of 46 prospective studies found that each 1% increase in HbA1c was associated with a 15-20% increase in cardiovascular events.
• Fasting insulin. The marker most doctors skip and arguably the most important one on this list. Insulin resistance precedes elevated glucose by years to decades. You can have a normal fasting glucose and dangerously high fasting insulin — this is the metabolic fire before the smoke.
• Lipid panel. Total cholesterol, LDL, HDL, and triglycerides. The triglyceride-to-HDL ratio is a stronger predictor of cardiovascular risk than LDL alone. A ratio above 3.5 signals insulin resistance and small dense LDL particles.

Inflammation

• hs-CRP (high-sensitivity C-reactive protein). A measure of systemic inflammation. Levels above 3.0 mg/L are associated with a near-doubling of cardiovascular risk compared to levels below 1.0 mg/L. Chronic low-grade inflammation drives aging at a cellular level — this marker tracks it.
• Homocysteine. An amino acid that accumulates when B-vitamin metabolism is impaired. Elevated homocysteine is independently associated with cardiovascular disease, cognitive decline, and bone fractures. It responds directly to B12, B6, and folate intake.

Nutrients

• Vitamin D (25-hydroxyvitamin D). The storage form. Men with sufficient vitamin D have significantly higher testosterone than deficient men. Most men eating a standard diet and working indoors are deficient.
• B12. Deficiency is common in men over 40 due to declining gastric acid production. Symptoms mimic aging — fatigue, cognitive fog, peripheral neuropathy — and are frequently attributed to “getting older” instead of tested for.
• Ferritin. The storage form of iron. Low ferritin means depleted iron stores. But high ferritin (above 300 ng/mL in men) is equally concerning — it acts as an inflammatory marker and is associated with insulin resistance.
• Magnesium (RBC). Request RBC magnesium, not serum magnesium. Serum levels are maintained at the expense of intracellular stores, meaning serum can read normal while your cells are depleted. RBC magnesium reflects true intracellular status.

Thyroid

• TSH (thyroid-stimulating hormone). The screening marker. Elevated TSH signals the pituitary is working harder to stimulate an underperforming thyroid.
• Free T3. The active thyroid hormone. T3 drives metabolic rate, energy production, and body temperature regulation. TSH can appear normal while free T3 is suboptimal.
• Free T4. The inactive precursor that converts to T3. A wide gap between T4 and T3 may indicate a conversion problem rather than a production problem.

Kidney and Liver

• BUN (blood urea nitrogen) and creatinine. Kidney filtration markers. Relevant for men eating high-protein diets — elevated BUN is expected with higher protein intake, but rising creatinine warrants attention.
• eGFR (estimated glomerular filtration rate). Derived from creatinine. The most direct measure of kidney function. Values below 60 mL/min for three or more months indicate chronic kidney disease.
• ALT and AST. Liver enzymes. Mild elevations can indicate non-alcoholic fatty liver disease, which affects an estimated 25% of the adult population. These markers often improve with fat loss and reduced refined carbohydrate intake.

Optimal Ranges vs. “Normal” Ranges

The reference ranges on your lab report describe the middle 95% of the testing population. That population includes sedentary, metabolically unhealthy individuals. “Normal” means you are not flagged for disease. It does not mean you are functioning well.

The distinction matters. A total testosterone of 300 ng/dL is “normal” by most lab ranges (roughly 264-916 ng/dL). It is also associated with fatigue, reduced muscle mass, and increased body fat in clinical studies. A fasting glucose of 99 mg/dL is “normal” but sits one point below a prediabetes diagnosis.

Here are the functional optimal ranges supported by research, alongside standard lab ranges. Discuss these with your doctor — they are targets to aim for, not diagnostic criteria.

Your doctor interprets results in the context of your full health picture. These ranges are reference points for the conversation, not self-diagnosis tools.

What the CRON Protocol Affects

If you are following the CRON meal plan or the Walford ingredient framework, here is what you should expect to see move on your labs — and the mechanisms behind those changes.

Fasting glucose and HbA1c. Calorie restriction with optimal nutrition consistently lowers both. The Biosphere 2 crew saw a 21% drop in fasting glucose on 1,750-2,100 calories per day. A controlled study of non-obese humans on 25% calorie restriction for two years found sustained reductions in fasting glucose and insulin.

Triglycerides. The same Biosphere 2 data showed a 30% reduction in total cholesterol. Triglycerides respond aggressively to reduced refined carbohydrates and increased omega-3 intake — both of which are built into the CRON framework via sardines, salmon, and the elimination of processed food.

hs-CRP. Calorie restriction reduces systemic inflammation. The CALERIE trial — the first controlled study of calorie restriction in non-obese humans — found significant reductions in CRP and TNF-alpha at two years.

Testosterone. Not directly, but through inputs. The CRON plan delivers 180% DV zinc and 110% DV magnesium from food, as documented in the zinc and magnesium article. Correcting these deficiencies restores testosterone production in deficient men. Vitamin D from salmon, sardines, and eggs further supports the androgenic pathway. The No TRT article covers this in detail.

Homocysteine. B12 from beef, eggs, sardines, and nutritional yeast keeps homocysteine in check. Folate from dark leafy greens and lentils completes the cycle. These are standard CRON ingredients.

Frequency and Cost

Test annually at minimum. If you are making significant dietary changes — starting the CRON protocol, shifting macros, adding or dropping supplements — test at baseline and again at 90 days. The No TRT article recommends exactly this cadence: baseline, intervene for 90 days, retest, compare.

Twice per year is the practical cadence for men actively working on body composition or metabolic health. Once you have two consecutive panels showing optimal ranges, annual testing is sufficient to maintain.

In most US states, you do not need a doctor’s order to get blood drawn. Direct-to-consumer lab services allow you to order the exact tests you want, walk into a local draw site, and receive results in 2-5 business days. A comprehensive panel covering everything in this article runs $200-400 out of pocket. That is the cost of two months of a middling supplement stack — except blood work actually tells you something.

If you have insurance, your doctor can order these through your standard lab. Some markers — fasting insulin, RBC magnesium, free T3 — may require a specific request. Print this list. Bring it to your appointment. A good doctor will order all of it. A great doctor was already going to.

The Sequence

1. Get the full panel drawn. Fasted, morning draw (testosterone peaks in the morning and declines throughout the day).
2. Record every number. Date it. This is your baseline.
3. Run the protocol for 90 days — CRON meals, kettlebells, rucking.
4. Retest at 90 days. Same lab, same conditions, morning fasted draw.
5. Compare the numbers. The data tells the story.

This is not medical advice. It is a framework for having a better conversation with your doctor — one where you show up with the data instead of the symptoms, and where “normal” is not good enough because you know what optimal looks like.