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Common blood tests explained: CBC, metabolic panel, cholesterol and A1C
What the most common blood tests measure, what high or low results can mean, why reference ranges vary, and what to ask about your results.
Key takeaways
- Most routine blood work includes a blood count, a metabolic panel and sometimes cholesterol and A1C.
- A result slightly outside the reference range is often not a problem on its own.
- Results are interpreted together with your symptoms, history and previous results.
Blood tests are among the most common medical tests. Understanding what they measure makes it easier to ask good questions — but always review results with the clinician who ordered them.
Complete blood count (CBC)
- Hemoglobin and hematocrit measure your blood’s oxygen-carrying capacity. Low values can mean anemia.
- White blood cells help fight infection. High counts can occur with infection or inflammation; low counts have many causes.
- Platelets help blood clot.
Basic or comprehensive metabolic panel (BMP or CMP)
- Glucose: blood sugar. A fasting result of 100–125 mg/dL (5.6–6.9 mmol/L) suggests prediabetes and 126 mg/dL (7.0 mmol/L) or higher on two tests suggests diabetes.
- Electrolytes such as sodium and potassium, which affect nerves, muscles and heart rhythm.
- Kidney function: creatinine and eGFR (estimated glomerular filtration rate).
- Liver tests (in the comprehensive panel): enzymes such as ALT and AST, plus bilirubin and albumin.
Lipid panel (cholesterol)
Measures total cholesterol, LDL (“bad”) cholesterol, HDL (“good”) cholesterol and triglycerides. Your target depends on your overall heart risk. See our guide to cholesterol.
Hemoglobin A1C
Shows your average blood sugar over about three months.
| A1C | What it suggests |
|---|---|
| Below 5.7% | Normal |
| 5.7% to 6.4% | Prediabetes |
| 6.5% or higher | Diabetes (usually confirmed with a repeat test) |
Other common tests
- TSH (thyroid-stimulating hormone) checks thyroid function.
- Vitamin B12, folate and ferritin help investigate tiredness and anemia.
- Urinalysis looks for infection, blood, protein and sugar in urine.
Why reference ranges vary
Each laboratory sets its own reference range, usually covering about 95% of healthy people. That means about 1 in 20 healthy people will have a result just outside the range for any single test. Ranges can also vary by age, sex and pregnancy. A slightly abnormal result often needs only a repeat test or nothing at all — your clinician will interpret it in context.
Preparing for a blood test
Ask whether you need to fast (some glucose and lipid tests require 8–12 hours without food), whether to take your usual medicines, and when results will be ready. Drink water unless told otherwise — it makes drawing blood easier.
Questions to ask about your results
- Which results are outside the range, and does that matter for me?
- How do these compare with my previous results?
- Do I need a repeat test, more tests, or any treatment?
- How can I get a copy of my results?
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Sources and further reading
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