When your doctor says your blood test is normal, they mean your results fall within the reference range - a statistical range derived from the middle 95% of the tested population. In a population where 70% of people are overweight and 50% are metabolically unhealthy, normal and optimal are very different things.
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Coeheal Editorial Team
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Coeheal Editorial Team
Editorially reviewed for accuracy against cited sources. This is an editorial review, not a medical or clinical review. For personalised health advice, consult a qualified healthcare professional.
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Laboratory reference ranges are established by testing a large population and defining the middle 95% as normal. This means 2.5% of healthy people will fall outside the normal range on any given test - and conversely, a result within the normal range does not mean it is optimal for health. The reference range problem is most acute for nutrients like vitamin D, where the normal range (20-100 ng/mL in most labs) includes levels associated with significantly increased disease risk at the lower end. A vitamin D level of 22 ng/mL is technically normal but is associated with substantially higher risk of respiratory infections, cardiovascular disease, and certain cancers compared to a level of 50 ng/mL. Always discuss your results with a healthcare provider before making significant changes to medications or supplements.
Red blood cells (RBC): normal 4.5-5.5 million/uL (men), 4.0-5.0 million/uL (women); low suggests anaemia. Haemoglobin: normal 13.5-17.5 g/dL (men), 12.0-15.5 g/dL (women); low haemoglobin defines anaemia. MCV (Mean Corpuscular Volume): normal 80-100 fL; low (microcytic) suggests iron deficiency; high (macrocytic) suggests B12 or folate deficiency. White blood cells: normal 4,500-11,000/uL; high suggests infection or inflammation; low suggests immune suppression. Ferritin (often ordered separately): normal 12-300 ng/mL (men), 12-150 ng/mL (women); optimal 50-150 ng/mL; low ferritin is the earliest sign of iron deficiency before haemoglobin falls; high ferritin (above 300 ng/mL) is associated with inflammation, metabolic syndrome, and haemochromatosis.
Fasting glucose: normal 70-99 mg/dL; prediabetes 100-125 mg/dL; diabetes 126 mg/dL or above; optimal 70-85 mg/dL. HbA1c: reflects average blood glucose over 2-3 months; normal below 5.7%; prediabetes 5.7-6.4%; diabetes 6.5% or above; optimal below 5.4%. Creatinine: normal 0.7-1.2 mg/dL (men), 0.5-1.0 mg/dL (women); elevated suggests reduced kidney function. eGFR: normal 60 mL/min/1.73m2 or above; optimal 90 or above; declining eGFR over time is more informative than a single value. ALT (liver enzyme): normal 7-56 U/L; elevated suggests liver inflammation; optimal below 25 U/L. Albumin: normal 3.5-5.0 g/dL; low suggests malnutrition, liver disease, or chronic inflammation.
LDL cholesterol: normal below 100 mg/dL (general population), below 70 mg/dL (high cardiovascular risk); LDL particle number (LDL-P) and particle size are better predictors of risk than LDL-C alone - small, dense LDL particles are more atherogenic than large, buoyant particles. HDL cholesterol: normal above 40 mg/dL (men), above 50 mg/dL (women); optimal above 60 mg/dL; low HDL is a stronger independent risk factor for cardiovascular disease than high LDL in many studies. Triglycerides: normal below 150 mg/dL; optimal below 100 mg/dL; the most modifiable lipid marker through diet (reducing refined carbohydrates and sugar has the largest effect). Total cholesterol:HDL ratio: optimal below 3.5; above 5 is high risk. Advanced markers worth requesting: ApoB (measures atherogenic particle number directly; optimal below 80 mg/dL); Lp(a) (genetically determined cardiovascular risk factor; elevated in 20% of the population; not modifiable by lifestyle; important to know if elevated above 50 mg/dL or 125 nmol/L).
Thyroid: TSH normal 0.4-4.0 mIU/L; optimal 1.0-2.5 mIU/L; TSH above 2.5 mIU/L may be associated with hypothyroid symptoms in some people. Free T4 normal 0.8-1.8 ng/dL; Free T3 normal 2.3-4.2 pg/mL. Thyroid antibodies (TPO-Ab, TG-Ab) elevated in Hashimoto thyroiditis. Vitamin D (25-hydroxyvitamin D): normal 20-100 ng/mL; optimal 40-60 ng/mL; deficient below 20 ng/mL; levels above 100 ng/mL may be associated with toxicity. High-sensitivity CRP (hs-CRP): optimal below 1.0 mg/L; 1-3 mg/L is moderate cardiovascular risk; above 3 mg/L is high risk. Homocysteine: normal below 15 umol/L; optimal below 10 umol/L; elevated homocysteine responds well to B12, folate, and B6 supplementation. Fasting insulin: normal 2-25 uIU/mL; optimal below 8 uIU/mL; elevated fasting insulin is the earliest sign of insulin resistance, often appearing years before fasting glucose rises. HOMA-IR (calculated from fasting glucose and insulin): optimal below 1.5; above 2.0 suggests significant insulin resistance.
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