How to Read a Blood Test: Understanding Your Lab Results

Blood test reports are easier to understand with a few basic principles.

Reference Ranges

• Each test has a normal range based on 95% of healthy people
• Ranges vary by lab, age, sex
• Outside range = flagged H (high) or L (low)

Key Principles

• Outside range is not always bad
• One abnormal value rarely means anything alone
• Patterns across multiple values are more meaningful
• Trends matter more than single values

Most Important Numbers

• Hemoglobin — oxygen (low = anemia)
• WBC — immune activity
• Platelets — clotting
• Glucose — blood sugar
• Creatinine/eGFR — kidneys
• ALT/AST — liver
• Sodium/Potassium — electrolytes
• LDL — cardiovascular risk

Red Flags Needing Prompt Attention

• Hemoglobin below 7 g/dL
• WBC above 30,000 or below 2,000
• Platelets below 50,000
• Potassium above 6.0 or below 2.8
• Glucose above 400 or below 50
• Sodium below 120

Questions for Your Provider

• Which values are outside range and how far?
• Is this new compared to my previous results?
• What could be causing this?
• Do we need more tests?
• When should we recheck?

Important

• Always discuss results with a qualified healthcare provider — online interpretation is educational, not diagnostic