Blood Work Decoder

How to Read Your Lab Results, Spot the Red Flags, and Know Exactly What to Do Next

Version 1.0 — March 2026

slimstudio.com

Chapter 1: How to Read Your Lab Report

You got bloodwork done. Your doctor said everything looks "normal." But you still feel like garbage — tired by 2pm, can't lose the gut, sleep is hit or miss, and your libido disappeared somewhere around age 37. Sound familiar?

Here's the problem: "normal" on a lab report means you fall within the reference range. That reference range is built from the general population — including sedentary, overweight, chronically stressed people who feel just as bad as you do. Being "normal" among sick people is not the same as being healthy.

This guide exists to close that gap. For every marker in your blood work, you'll learn three things:

1. What it measures — in plain English, not medical jargon
2. Where yours should be — the optimal range, not just the lab "normal"
3. What to do if it's off — specific, actionable next steps

Anatomy of a Lab Result

Every line on your lab report has four pieces of information:

• The marker name — what was tested (e.g., "Testosterone, Total")
• Your value — the number from your blood sample
• The unit — how it's measured (ng/dL, mg/dL, mIU/L, etc.)
• The reference range — what the lab considers "normal"

If your value falls outside the reference range, it gets flagged — usually with an "H" for high or "L" for low. But many of the most important problems hide inside the reference range. A testosterone level of 280 ng/dL is technically "normal" (the range goes down to 264), but a 42-year-old man at 280 will feel terrible. That's why this guide uses optimal ranges alongside the lab normals.

How to Use This Guide

This is a reference guide, not a story. You don't need to read it front to back. Pull up your lab results, find the marker you're looking at, and flip to the relevant section. Each marker includes the optimal range, what it means if you're high or low, and what to do about it.

Chapter 7 ties it all together with real-world scenarios. If you want to see how the markers interact as a system, start there after reviewing your individual numbers.

Testing Best Practices

Before we get into the markers, here's how to make sure your results are accurate. Bad testing conditions produce bad data, and bad data leads to bad decisions.

Chapter 2: Hormones

This is the chapter most men flip to first. Hormones control energy, body composition, mood, libido, and recovery. When they're off, everything feels off. The trick is that these markers work as a system — you can't evaluate testosterone in isolation. You need to see the full picture: how much you make, how much is available, what's binding it up, and what it's converting into.

• Below 500 ng/dL: Most men start experiencing symptoms — fatigue, brain fog, declining libido, difficulty losing fat. Worth investigating further with Free T and SHBG.
• Below 300 ng/dL: Clinical threshold for hypogonadism. If confirmed on two separate morning draws, this is typically where TRT conversations begin.
• Above 1000 ng/dL: If natural, this is unusual after age 35. If on TRT, your dose may be higher than needed. More is not always better — high levels increase hematocrit and estrogen conversion.

• Below 10 ng/dL: You will almost certainly have symptoms regardless of Total T. Common cause: elevated SHBG binding up available testosterone.
• Below 15 ng/dL with good Total T: Check SHBG. If SHBG is high (>50 nmol/L), the problem isn't production — it's bioavailability.
• 15–25 ng/dL: Where most men feel their best. Energy, libido, and body composition tend to be well-supported here.

• Above 50 nmol/L: Your Free T is likely low even if Total T looks fine. Address the cause — check thyroid function, review diet (chronic low-carb can elevate SHBG), and rule out liver issues.
• Below 15 nmol/L: Often a sign of insulin resistance. Get fasting insulin and HOMA-IR tested. This usually improves with weight loss and metabolic health interventions.

• Below 20 pg/mL: Joint pain, low mood, dry skin, poor libido. Low estradiol is just as problematic as high. If you're on an aromatase inhibitor, this is likely over-suppressed — discuss reducing the dose with your doctor.
• 20–30 pg/mL: Sweet spot. Joint health, mood, libido, and cardiovascular protection are all supported here.
• Above 40 pg/mL with symptoms: Water retention, bloating, nipple sensitivity, mood swings. Options: more frequent, smaller testosterone injections (reduces aromatization spikes), body fat reduction, or a low-dose aromatase inhibitor as a last resort.
• Above 40 pg/mL without symptoms: Monitor. Don't treat a number — symptoms matter more than the value. Many men function well at 35-45 pg/mL.

• Low T + Low LH/FSH: Secondary hypogonadism. The pituitary isn't sending the signal. Causes include obesity, sleep apnea, chronic stress, opioid use, or a pituitary issue. This is often reversible by fixing the underlying cause.
• Low T + High LH/FSH: Primary hypogonadism. The pituitary is screaming for more testosterone but the testes can't deliver. More likely to require TRT.
• On TRT: LH and FSH will be near zero. This is expected — exogenous testosterone shuts down the HPG axis. Testing them while on TRT is pointless unless checking for compliance.

• 15–25 ng/mL: Mildly elevated. Check for common causes: stress, sleep deprivation, chest wall stimulation, certain antidepressants (SSRIs) or antipsychotics. Retest before investigating further.
• Above 25 ng/mL consistently: Warrants a pituitary MRI to rule out a prolactinoma (benign tumor). These are treatable with medication — don't panic, but don't ignore it.
• Symptoms of high prolactin: Low libido, erectile dysfunction, headaches, visual changes (if pituitary mass is large).

• Below 200 μg/dL: May indicate adrenal fatigue or chronic stress depleting DHEA. Consider supplementing with 25-50mg DHEA daily under medical supervision, especially if cortisol is also off.
• On TRT: DHEA-S may decline further since the HPG axis is suppressed. Some clinicians add low-dose DHEA to TRT protocols for this reason.

Chapter 3: Metabolic Markers

If hormones are the engine, metabolic markers are the fuel system. These numbers tell you how well your body processes energy — specifically, how it handles glucose and fat. Metabolic dysfunction is the root cause of most chronic disease in men over 35, and it almost always shows up in bloodwork before symptoms become obvious.

The markers in this chapter interact as a system. Elevated fasting glucose alone might not mean much. But elevated fasting glucose plus high fasting insulin plus a high triglyceride-to-HDL ratio paints a clear picture of insulin resistance.

• 75–95 mg/dL: Healthy insulin sensitivity. Your body clears glucose efficiently overnight.
• 95–99 mg/dL: Technically "normal" but trending in the wrong direction. This is where lifestyle intervention has the most leverage — don't wait for it to cross 100.
• 100–125 mg/dL: Prediabetes range. Insulin resistance is established. Actionable: cut refined carbs, add post-meal walks, get fasting insulin and HbA1c tested for the full picture.
• 126+ mg/dL (confirmed twice): Diagnostic threshold for type 2 diabetes. See your doctor. This is manageable — but ignoring it is not an option.

• Below 5.4%: Excellent metabolic control. Keep doing what you're doing.
• 5.4–5.6%: Still "normal" but worth watching. Optimize diet, add walking after meals, prioritize sleep.
• 5.7–6.4%: Prediabetes. This is the intervention window — with consistent dietary changes and exercise, most men can drop 0.5–1.5% in 8-12 weeks. A 5.7% A1c is not a death sentence. It's a wake-up call with a clear path back.
• 6.5%+: Diabetes range. Work with your doctor on a treatment plan. Medication may be appropriate alongside lifestyle changes.

• Below 8 μIU/mL: Healthy insulin sensitivity. Your pancreas isn't working hard to keep glucose in check.
• 8–12 μIU/mL: Early insulin resistance. Glucose might still look fine, but the system is straining. This is the earliest warning sign — act now.
• Above 12 μIU/mL: Established insulin resistance. Your body needs excess insulin to manage glucose. Intervention: reduce refined carbs to under 100g/day, prioritize protein (0.7–1g per pound bodyweight), resistance training 3x/week, and post-meal walks.

• Below 1.0: Excellent insulin sensitivity. Low metabolic risk.
• 1.0–2.0: Mild insulin resistance. Addressable with lifestyle changes.
• Above 2.5: Significant insulin resistance. This strongly predicts future type 2 diabetes if unaddressed. Full metabolic intervention: clean eating, time-restricted feeding (8-10 hour window), resistance training, and 7,000–10,000 daily steps.

• Below 1.5: Excellent. Low cardiovascular risk, good insulin sensitivity.
• 1.5–2.0: Acceptable. Room for improvement.
• Above 3.0: Strong indicator of insulin resistance and atherogenic lipid profile. Even if LDL looks "normal," a high Trig:HDL ratio suggests dangerous small dense LDL particles. Intervention: reduce sugar and refined carbs, increase omega-3 intake (fatty fish 2-3x/week or 2g EPA/DHA supplement), and exercise consistently.

Chapter 4: Inflammation & Stress

Chronic inflammation is the slow burn behind almost every metabolic problem. It damages blood vessels, impairs insulin signaling, accelerates aging, and makes recovery from training harder. Stress hormones — particularly cortisol — both drive and are driven by inflammation. These markers help you catch the fire before it becomes a wildfire.

• Below 1.0 mg/L: Low cardiovascular risk. Low systemic inflammation. This is where you want to be.
• 1.0–3.0 mg/L: Moderate risk. Something is driving inflammation — visceral fat, poor diet, poor sleep, chronic stress, or subclinical infection. Investigate and address.
• Above 3.0 mg/L: High risk. Significant systemic inflammation. Can be driven by: obesity (especially visceral fat), smoking, periodontal disease, autoimmune conditions, or chronic infection. This needs attention.
• Above 10 mg/L: Likely acute inflammation — recent infection, injury, or illness. Retest in 2-3 weeks once the acute cause resolves.

Interventions that reliably lower CRP: weight loss (especially visceral fat), omega-3 supplementation (2g+ EPA/DHA daily), regular exercise, improved sleep, and reducing refined sugar and seed oil intake.

• Below 10 μmol/L: Healthy. B vitamin status is likely adequate.
• 10–15 μmol/L: Mildly elevated. Often responds to a methylated B-complex supplement (methylfolate + methylcobalamin + P5P). Check B12 levels if not already tested.
• Above 15 μmol/L: Significantly elevated. Cardiovascular risk is increased. Supplement with methylated B vitamins and retest in 3 months. If it doesn't respond, investigate MTHFR polymorphism.

• Below 10 mm/hr: Normal. No significant inflammation.
• 10–20 mm/hr: Mildly elevated. Could be aging, minor illness, or low-grade inflammation. Context matters.
• Above 20 mm/hr consistently: Investigate. Combined with elevated CRP, this confirms systemic inflammation. Look for a source — chronic infection, autoimmune activity, or metabolic dysfunction.

If cortisol is high: prioritize sleep (7-9 hours, consistent schedule), limit caffeine to before 2 PM, add 10-30 minutes of morning sunlight exposure, and avoid intense exercise after 6 PM. Supplements with evidence for cortisol reduction: phosphatidylserine (100-300mg evening), ashwagandha (300-600mg), and magnesium glycinate (200-400mg before bed).

If cortisol is low: support adrenal function with vitamin C (500-1000mg), a B-complex (especially B5), and rhodiola (200-400mg in the morning). Don't train intensely until cortisol normalizes — stick to walking and light resistance work under 45 minutes.

Chapter 5: Thyroid

Your thyroid gland sets the metabolic rate for every cell in your body. When it's sluggish, everything slows down — energy, fat burning, cognition, mood, recovery. The frustrating part: most doctors only test TSH. That's like checking the thermostat without checking the furnace. A complete thyroid panel requires four markers: TSH, Free T4, Free T3, and ideally Reverse T3.

Thyroid dysfunction is massively underdiagnosed because of overly broad reference ranges. A TSH of 4.0 is technically "normal" but a significant number of people experience hypothyroid symptoms at that level. The evidence increasingly supports tighter optimal ranges.

• 0.5–2.5 mIU/L: Optimal. Thyroid stimulation is well-calibrated.
• 2.5–4.5 mIU/L: "Normal" but suboptimal. If you have symptoms (fatigue, weight gain, cold intolerance, hair thinning, constipation), this level warrants further investigation with Free T3 and Free T4. Many functional medicine providers consider treatment above 2.5 if symptomatic.
• Above 4.5 mIU/L: Hypothyroidism. The pituitary is working overtime to stimulate a sluggish thyroid. Check thyroid antibodies (TPO, TgAb) to rule out Hashimoto's thyroiditis, the most common cause.
• Below 0.4 mIU/L: Possible hyperthyroidism or over-medication. Symptoms: anxiety, rapid heart rate, weight loss, tremor. Requires medical evaluation.

• 1.0–1.5 ng/dL: Good production. Adequate raw material for T3 conversion.
• Below 1.0 ng/dL: Low production. If TSH is also elevated, this confirms hypothyroidism. If TSH is normal or low, this could indicate a pituitary problem (central hypothyroidism) — less common but worth investigating.

• 3.0–4.0 pg/mL: Active metabolism is well-supported. Energy and fat burning should be functioning.
• Below 3.0 pg/mL: Conversion may be impaired even if TSH and T4 look fine. Investigate: chronic stress (cortisol), very low-carb dieting (reduces T4-to-T3 conversion), selenium deficiency, or liver issues. Selenium supplementation (200 mcg/day) supports conversion.
• Below 2.5 pg/mL with symptoms: You're functionally hypothyroid regardless of what TSH says. Many men with "normal" thyroid labs feel terrible because nobody checked Free T3.

• Below 15 ng/dL: Normal. Conversion is favoring the active T3 pathway.
• Above 15 ng/dL with low Free T3: Your body is shunting T4 into the inactive pathway. Most common causes: chronic stress, chronic dieting, illness, inflammation. Fix the root cause — you can't supplement your way past a stress-driven conversion problem.
• Free T3 to Reverse T3 ratio: Some clinicians use this ratio (Free T3 in pg/mL × 10 ÷ Reverse T3 in ng/dL). A ratio above 2.0 is generally considered healthy. Below 1.5 suggests significant conversion issues.

Chapter 6: Liver, Kidney & Blood

These markers are your body's infrastructure report. Your liver processes everything — hormones, toxins, medications, alcohol. Your kidneys filter waste and regulate fluid balance. Your blood carries oxygen to every tissue. When these systems are strained, everything else suffers. On TRT or any hormone protocol, monitoring these is non-negotiable.

• Below 30 U/L: Healthy liver function. No concerns.
• 30–56 U/L: Within lab range but suboptimal. Common culprits: alcohol (even moderate), acetaminophen, statins, fatty liver (NAFLD), or recent intense exercise. Retest after eliminating the variable.
• Above 56 U/L: Flagged high. If persistent, investigate: liver ultrasound, check alcohol intake, review medications. On TRT: oral testosterone and some ancillary drugs (oral AI medications) can elevate liver enzymes — injectable testosterone typically does not.

• Below 30 U/L: Healthy. Low oxidative stress.
• 30–65 U/L: Mildly elevated. Review alcohol intake, body fat level (NAFLD), and medications. GGT above 30 has been associated with increased metabolic syndrome risk even when other liver markers are normal.
• Above 65 U/L: Investigate. Ultrasound if persistent. Eliminate alcohol for 30 days and retest — if it normalizes, you have your answer.

• Creatinine above 1.3 mg/dL: May indicate reduced kidney function, but muscular men and creatine supplementation can both elevate creatinine without actual kidney impairment. Context matters — a lean 200lb man who takes 5g creatine daily will have higher creatinine than average. Check eGFR for the full picture.
• BUN above 20 mg/dL: Can indicate dehydration, high protein diet, or reduced kidney function. If you eat 200g+ protein daily, mildly elevated BUN is expected and not concerning if creatinine and eGFR are normal.
• eGFR below 90: Mild reduction. Warrants monitoring. Below 60 is clinically significant kidney disease. Stay well-hydrated, limit NSAIDs (ibuprofen, naproxen), and discuss with your doctor.

• Hematocrit 42–50%: Healthy range. Good oxygen delivery without viscosity risk.
• Hematocrit 50–52%: Monitor. Stay well-hydrated (80-100 oz water daily). Retest in 2-4 weeks to rule out dehydration as a cause. Many "high" readings are simply dehydration.
• Hematocrit 52–54%: Consider therapeutic phlebotomy (blood donation). One unit (~500mL) drops hematocrit by 2-3%. Don't donate more than every 8 weeks.
• Hematocrit above 54%: Significant risk. Discuss dose reduction with your doctor if on TRT. Also consider more frequent, smaller injections — large infrequent doses cause bigger hematocrit spikes.

• Below 50 ng/mL: Iron depletion. You may feel fatigued, weak, and cold even if hemoglobin is still in range. Supplement with iron bisglycinate (better absorbed, less GI distress) and retest in 3 months. Especially common in men who donate blood frequently.
• 50–150 ng/mL: Well-stocked. No action needed.
• Above 300 ng/mL: Elevated. Could be inflammation (check CRP), liver disease (check ALT), or hereditary hemochromatosis. Get genetic testing for HFE gene if persistently elevated without other explanation.

Chapter 7: Putting It All Together

Individual markers tell you what's happening in one system. But your body doesn't work in isolation — hormones affect metabolism, inflammation affects hormones, thyroid affects everything. This chapter walks through four real-world scenarios showing how to read a panel as a complete picture and decide what to do next.

Chapter 8: What's Next

You've decoded your labs. You know where you stand. Now what?

Testing Schedule

How often you retest depends on what you found and what you're doing about it:

• Everything looks good: Retest in 6-12 months. Annual comprehensive bloodwork is the minimum for any man over 35 who takes health seriously.
• Making lifestyle changes (diet, exercise, supplements): Retest in 90 days. That's enough time for A1c, lipids, and hormone levels to respond to real changes.
• Starting or adjusting TRT: Retest at 6-8 weeks. Your levels need that long to stabilize on a new protocol. Test at trough. Include Total T, Free T, E2 (sensitive), and CBC at minimum.
• Something was flagged concerning: Follow your doctor's recommendation. Don't wait 90 days to recheck a glucose of 132 or a hematocrit of 54.

The Minimum Annual Panel

If you only get one comprehensive blood panel per year, make sure it includes these markers. Print this list and hand it to your doctor.

Add these if indicated by your situation:

• On TRT: PSA (if over 40), LH/FSH (baseline only), prolactin
• Suspected thyroid issues: Reverse T3, thyroid antibodies (TPO, TgAb)
• Cardiovascular risk: Homocysteine, Lp(a), ApoB
• Adrenal/stress concerns: Morning cortisol, DHEA-S, 4-point salivary cortisol

Free Resources at slimstudio.com

We publish in-depth articles on every topic covered in this guide. All free, no paywalls.

• How to Read Your TRT Labs — deep dive on testosterone, SHBG, and estradiol interpretation
• Lab Cheat Sheet: TT, FT & SHBG — quick reference card for hormone markers
• When to Test Hormones — timing rules for accurate results
• TRT Lab Schedule — the 5-phase testing protocol from baseline through long-term maintenance
• HCT & HGB on TRT — managing hematocrit and hemoglobin safely
• Lower Your A1c in 8-12 Weeks — the complete metabolic intervention protocol
• Cortisol 101 — understanding and fixing your stress hormone rhythm

Other Slim Studio Guides

• The Metabolic Reset ($7) — a 4-week protocol to fix blood sugar, restore energy, and start losing fat. The lifestyle foundation that makes your bloodwork improve.
• Meal Planning Template ($7) — 4 weeks of high-protein, blood-sugar-friendly meals with macros, shopping lists, and prep guides.
• Recovery Protocol ($9) — sleep optimization, stress management, and supplement stacking for men who train but don't recover.
• Complete Bundle ($19) — all four guides at a discount. The full system.

Knowledge is step one. Action is step two. Your bloodwork is a map — it shows you exactly where you are and exactly what needs to change. The protocols in our other guides are built to move those numbers. Pick the one that matches your biggest gap and get to work.