How to Read Your Blood Test Results

The first thing to understand about blood test reference ranges: they're statistical, not clinical. The "normal range" for any given marker is typically defined as the values that fall within two standard deviations of the mean for a healthy reference population — meaning roughly 95% of "healthy" people fall within the range. That definition has several implications most people don't think about:

• "Normal" includes a wide spread. A vitamin D level of 30 ng/mL and a level of 80 ng/mL are both technically "normal" but represent very different states of vitamin D sufficiency. Same with ferritin (12 vs 150), TSH (0.5 vs 4.5), and most other markers. The range is broad on purpose so that few people get flagged unnecessarily.
• "Normal" isn't always healthy. The reference population includes people with subclinical issues that haven't yet developed into diagnosable disease. So the "normal range" for some markers (notably TSH, ferritin, vitamin D) includes values that functional medicine practitioners would consider suboptimal. The range was designed to catch overt disease, not to define optimal health.
• Optimal ranges are tighter than normal ranges. Many specialists and researchers define "optimal" subranges within the normal range that correlate with better long-term outcomes. For example: TSH optimal is 0.5-2.5 (vs normal 0.5-4.5); ferritin optimal is 50-100 ng/mL (vs normal 11-307); vitamin D optimal is 40-60 ng/mL (vs normal 20-100).
• Reference ranges vary by lab. Quest, Labcorp, and BioReference each use slightly different reference ranges based on their own reference populations and assay methodology. A "normal" TSH at Quest might be a borderline TSH at Labcorp. This is why we recommend staying with one lab for longitudinal tracking.

The practical implication: don't interpret your results as just "normal vs flagged." Look at WHERE in the normal range your values fall. A vitamin D of 22 ng/mL is "normal" but at the low end and clinically meaningful; a ferritin of 18 ng/mL is "normal" but probably contributing to fatigue. Bring this nuance to your doctor's appointment — if you're "normal" but symptomatic, the where-in-range matters.

The most common markers you'll see on a basic blood test report, what they measure, and how to interpret typical values:

Complete Blood Count (CBC):

• WBC (White Blood Cells) — infection-fighting cells. High = infection, inflammation, stress. Low = viral illness, immune issues, marrow problems. Normal: ~4.5-11 K/µL.
• RBC (Red Blood Cells) — oxygen carriers. Low = anemia, blood loss. High = dehydration, lung disease, high altitude. Normal: ~4.5-5.9 (men), 4.0-5.2 (women) M/µL.
• Hemoglobin (Hgb) — the protein in RBCs that carries oxygen. Most direct measure of anemia. Normal: 13.5-17.5 g/dL (men), 12.0-15.5 g/dL (women).
• Hematocrit (Hct) — percentage of blood volume that's RBCs. Tracks with Hgb.
• Platelets — clotting cells. Low = bleeding risk. High = clotting risk. Normal: ~150-400 K/µL.
• MCV (Mean Cell Volume) — average RBC size. Low = iron deficiency, thalassemia. High = B12/folate deficiency, hypothyroidism. Normal: ~80-100 fL.

Comprehensive Metabolic Panel (CMP):

• Glucose — blood sugar. Fasting normal: 70-99 mg/dL. 100-125 = prediabetes. 126+ = diabetes (on two separate tests).
• BUN, Creatinine, eGFR — kidney function. eGFR above 90 = normal kidney function. eGFR 60-89 = mild reduction (common with age). Below 60 sustained = chronic kidney disease.
• Sodium, Potassium, Chloride, CO₂ — electrolytes; abnormalities suggest hydration, kidney, or medication issues.
• Calcium — bone health, parathyroid function. Normal: ~8.5-10.5 mg/dL.
• ALT, AST — liver enzymes. Elevated = liver inflammation (fatty liver, alcohol, medications, hepatitis, etc.).
• Alkaline Phosphatase, Bilirubin — bile flow and liver function.
• Total Protein, Albumin — overall protein status; low albumin suggests liver disease, kidney loss, or malnutrition.

Lipid Panel:

• Total Cholesterol — sum of all cholesterol. Aim <200 mg/dL. Less useful alone than the breakdown.
• LDL Cholesterol — "bad" cholesterol; the main target for cardiovascular risk reduction. Optimal <100 mg/dL, less than 70 if high risk.
• HDL Cholesterol — "good" cholesterol. Higher is generally better. Target >60 mg/dL ideal; <40 men / <50 women is low.
• Triglycerides — blood fats. Normal <150 mg/dL; high suggests metabolic syndrome, alcohol, or sugar intake.
• ApoB (Apolipoprotein B) — counts atherogenic particles; better cardiac risk predictor than LDL. Optimal <90 mg/dL; ideal for prevention <80.
• Lp(a) Lipoprotein(a) — genetically determined cardiac risk. Test once in your life. Normal <30 mg/dL; elevated >30, high >50.

Diabetes Markers:

• Hemoglobin A1c — 90-day average blood sugar. Normal <5.7%. Prediabetes 5.7-6.4%. Diabetes 6.5%+. Functional optimal <5.4%.
• Fasting Glucose — single-point blood sugar. Normal <100 mg/dL.
• Fasting Insulin — rises before A1c becomes abnormal. Normal 2-20 µIU/mL; functional optimal <7 µIU/mL.

Thyroid Markers:

• TSH — pituitary signal. Normal 0.5-4.5 mIU/L. Functional optimal 0.5-2.5. High = underactive thyroid; Low = overactive.
• Free T4 — storage thyroid hormone. Normal 0.8-1.8 ng/dL.
• Free T3 — active thyroid hormone. Normal 2.3-4.2 pg/mL.
• TPO Antibodies — autoimmune (Hashimoto's) marker. Should be negative; any elevation is meaningful.

Inflammation:

• hs-CRP (High-Sensitivity CRP) — vascular inflammation. Below 1.0 mg/L = low cardiac risk; 1.0-3.0 = moderate; above 3.0 = high.

Vitamins and Minerals:

• Vitamin D, 25-Hydroxy — Normal 20-100 ng/mL. Functional optimal 40-60.
• Vitamin B12 — Normal 200-900 pg/mL. Functional optimal 500-900.
• Ferritin — iron stores. Normal 11-307 ng/mL. Functional optimal 50-100. Below 30 commonly causes symptoms even though "normal."
• Folate — Normal >3.0 ng/mL; ideal >7.

Your lab report uses flags ("H" for high, "L" for low, sometimes colored bars or arrows) to indicate values outside the reference range. Here's the framework for what to do with each:

Step 1: Look at how far out of range it is.

• Slightly out of range (just above or below the cutoff): often clinically insignificant or a temporary variation. Retest in 4-12 weeks before treating. Hydration, recent meals, recent exercise, stress, time of day, and even the position you were in during the blood draw can shift many markers by 10-20%.
• Moderately out of range (1.5-3x outside the cutoff): meaningful and worth investigating. Retest to confirm, then evaluate underlying causes.
• Significantly out of range (3-10x or more outside the cutoff): typically clinically actionable. Don't wait to retest; bring to a medical provider promptly. Some values (very low hemoglobin, very high potassium, very high troponin, very low blood sugar) are urgent.

Step 2: Look at the pattern. One abnormal value in isolation often means less than several abnormal values in a related pattern. For example:

• One elevated liver enzyme = monitor; could be diet, medication, recent alcohol use, recent exercise.
• Multiple elevated liver enzymes (ALT + AST + alkaline phosphatase + bilirubin) = liver issue worth investigating.
• One slightly elevated TSH = often a fluke; retest in 8-12 weeks.
• Slightly elevated TSH + low-normal Free T4 + positive TPO antibodies = early Hashimoto's pattern.

Step 3: Don't act on a single abnormal result. The medical standard is to retest a flagged value before starting treatment, unless the value is significantly out of range or the situation is urgent. Day-to-day variation in many markers is large enough that a single abnormal value can be a fluke. Wait 4-12 weeks (the appropriate window depends on the marker — A1c reflects 90 days so retest in 3 months; lipid panel can be retested in 4-6 weeks; ferritin can be retested in 6-12 weeks after any iron supplementation).

Step 4: Bring results to a provider for interpretation. Lab values exist in clinical context. The same value can mean different things in different patients. A low fasting glucose of 65 in a healthy person is fine; in a diabetic on insulin it's concerning. A B12 of 350 is fine for most people but borderline for a vegan or someone on metformin. A provider who knows your history can interpret values in context.

Step 5: Track over time. Establish a longitudinal record. A vitamin D of 30 ng/mL is "borderline normal" — but if you were at 45 last year and 38 the year before, the trajectory tells you to address it before it becomes a deficiency. Same with A1c trending up (4.9 → 5.1 → 5.4), fasting insulin trending up, lipids drifting in the wrong direction. The trend matters more than any single snapshot.

A quick reference for the abbreviations you'll see on a typical blood test report:

• A1c (HbA1c, Hemoglobin A1c) — glycated hemoglobin; 90-day average blood sugar
• ALT — alanine aminotransferase; liver enzyme
• AST — aspartate aminotransferase; liver enzyme (also some non-liver sources)
• BUN — blood urea nitrogen; kidney function marker
• CBC — complete blood count
• CMP — comprehensive metabolic panel
• CRP — C-reactive protein; inflammation marker
• eGFR — estimated glomerular filtration rate; calculated kidney function
• Free T3 / Free T4 — unbound thyroid hormones
• FSH — follicle-stimulating hormone
• GGT — gamma-glutamyl transferase; liver enzyme, often elevated with alcohol use
• HDL — high-density lipoprotein ("good" cholesterol)
• Hgb / Hct — hemoglobin / hematocrit
• hs-CRP — high-sensitivity CRP; refined inflammation marker for cardiovascular risk
• LDL — low-density lipoprotein ("bad" cholesterol)
• LH — luteinizing hormone
• MCV — mean corpuscular volume; average red blood cell size
• Lp(a) — lipoprotein(a); genetic cardiac risk marker
• PSA — prostate-specific antigen
• PT / PTT / INR — clotting time markers
• RBC / WBC — red blood cells / white blood cells
• RDW — red cell distribution width; variation in RBC size
• SHBG — sex hormone-binding globulin
• TIBC — total iron-binding capacity
• TSH — thyroid-stimulating hormone

Units cheatsheet: Most US lab reports use these units. International (SI) units differ — if you're comparing US results to international lab work, conversion is required.

• mg/dL — milligrams per deciliter (cholesterol, glucose, calcium, BUN, creatinine)
• g/dL — grams per deciliter (hemoglobin, albumin, total protein)
• ng/mL or ng/dL — nanograms per milliliter or deciliter (vitamin D, ferritin, free T4)
• pg/mL — picograms per milliliter (B12, free T3, estradiol)
• µIU/mL or mIU/L — micro-international units or milli-international units per liter (TSH, insulin)
• U/L — units per liter (liver enzymes ALT, AST, GGT)
• K/µL or M/µL — thousands or millions per microliter (cell counts)
• % — percentage (A1c, hematocrit)