Common Medical Blood Tests: What Every Result Means
How to Use This Reference
This guide covers the blood tests most commonly ordered in primary care and preventive health settings. For each test, you will find what it measures, why it matters, what abnormal results indicate, and — importantly — the difference between standard clinical thresholds and the more ambitious targets that longevity-focused medicine pursues.
Metabolic Panel Tests
Glucose (Fasting)
What it measures: Blood sugar concentration after an 8-hour fast. Why it matters: Elevated fasting glucose reflects impaired insulin-mediated glucose disposal. Standard normal: Below 100 mg/dL | Optimal: Below 85 mg/dL
HbA1c (Glycated Hemoglobin)
What it measures: Percentage of hemoglobin with glucose attached — reflects 3-month average glucose. Standard normal: Below 5.7% | Optimal: Below 5.2%
Fasting Insulin
What it measures: Circulating insulin in a fasted state. Standard normal: Below 25 μIU/mL | Optimal: Below 5 μIU/mL
BUN (Blood Urea Nitrogen)
What it measures: Urea nitrogen, a protein metabolism byproduct cleared by kidneys. Elevated BUN suggests: Dehydration, high protein intake, reduced kidney perfusion, kidney disease. Standard normal: 7–20 mg/dL
Creatinine
What it measures: Muscle metabolism waste product filtered by kidneys. Elevated suggests: Reduced kidney filtration capacity. Standard normal (men): 0.7–1.2 mg/dL | (women): 0.5–1.0 mg/dL
eGFR (Estimated GFR)
What it measures: Estimated kidney filtration rate — a direct measure of kidney function. Standard normal: Above 90 mL/min/1.73m²
Liver Tests
ALT
What it measures: Liver cell enzyme — rises when hepatocytes are damaged or stressed. Optimal: Below 30 (men); below 19 (women) U/L
AST
What it measures: Found in liver and muscle; less specific than ALT. Elevated in isolation (without ALT elevation): Suggests muscle breakdown rather than liver disease.
GGT
What it measures: Enzyme sensitive to alcohol, fatty liver, and bile duct issues. Optimal: Below 20 (women); below 30 (men) U/L
Bilirubin (Total)
What it measures: Hemoglobin breakdown product. Elevated direct bilirubin: Bile duct obstruction. Elevated indirect bilirubin: Increased red cell breakdown or Gilbert's syndrome.
Lipid Tests
LDL-C
Standard normal: Below 130 mg/dL | Longevity optimal: Below 70 mg/dL
HDL-C
Standard normal (men): Above 40 | (women): Above 50 mg/dL | Optimal: Above 60 mg/dL
Triglycerides
Standard normal: Below 150 mg/dL | Optimal: Below 80 mg/dL
ApoB
What it measures: Number of atherogenic lipoprotein particles (more accurate than LDL-C). Optimal: Below 80 mg/dL
Thyroid Tests
TSH
Optimal range: 0.5–2.0 mIU/L (standard "normal" range is broader: 0.4–4.5)
Free T4
Target: Mid-to-upper half of reference range.
Free T3
Target: Upper third of reference range. Low T3 with normal TSH = conversion dysfunction.
Complete Blood Count
Hemoglobin
Men optimal: 14.5–17.5 g/dL | Women optimal: 13.0–15.5 g/dL
MCV
Low MCV: Iron deficiency or thalassemia. High MCV: B12 or folate deficiency.
Platelets
Normal: 150,000–400,000 per µL
Inflammatory Markers
hs-CRP
Optimal: Below 1.0 mg/L | Elevated risk: Above 3.0 mg/L
Ferritin
Optimal for energy: 70–100 ng/mL | Low: Below 30 ng/mL (symptomatic iron depletion)
Hormone Tests
Testosterone (Total) — Men
Optimal morning level: 600–1,000 ng/dL | Clinical hypogonadism threshold: Below 300 ng/dL
Cortisol (Morning, Fasting 7–9 AM)
Normal morning range: 10–20 µg/dL | High chronic cortisol suggests HPA axis dysregulation.
DHEA-S
Marker of adrenal reserve: Declines with age; optimal levels vary by age and laboratory.
Disclaimer: The information in this article is for educational and informational purposes only. It is not intended as medical advice. Always consult a qualified medical professional or doctor for any health-related questions or concerns.
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