Understanding Your Basic Labs: CBC, CMP, and Cholesterol

If you've ever gotten a packet of lab results, glanced at the green checkmarks, and put it in a drawer, you're not alone. Here's what's actually being measured, and which numbers are worth a closer look.

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CBC — Complete Blood Count

The CBC counts and characterizes the cells in your blood.

Red blood cells, hemoglobin, hematocrit — your oxygen-carrying capacity.

• Low: anemia. Most often iron deficiency (women), B12 deficiency, chronic inflammation, or blood loss.
• High: dehydration, smoking, sleep apnea, occasionally a primary blood disorder.

MCV, MCH, MCHC — the size and hemoglobin content of red cells. These tell you what KIND of anemia.

• Low MCV (microcytic): usually iron deficiency.
• High MCV (macrocytic): usually B12 or folate deficiency, sometimes alcohol or thyroid.

White blood cells (WBC) and differential — your immune system.

• High WBC: infection, inflammation, stress, sometimes leukemia.
• Low WBC: viral infection, autoimmune disease, some medications.
• The differential (neutrophils, lymphocytes, monocytes, eosinophils, basophils) tells you what kind of immune challenge.

Platelets — clotting.

• Low: bleeding risk, autoimmune (ITP), viral, certain medications.
• High: inflammation, iron deficiency, sometimes a primary marrow issue.

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CMP — Comprehensive Metabolic Panel

The CMP is your chemistry — kidneys, liver, electrolytes, glucose.

Glucose (fasting) — your blood sugar at rest.

• 100–125 mg/dL: pre-diabetes range.
• ≥126 mg/dL on two occasions: diabetes.
• I care about this even when it's "normal" — high-normal fasting glucose in your 40s often becomes diabetes in your 50s.

Sodium, potassium, chloride, bicarbonate — electrolytes. Tightly regulated; abnormalities usually mean medication effect, dehydration, kidney issues, or hormonal disorders.

BUN and creatinine — kidney function. The eGFR (estimated glomerular filtration rate) is the most useful single number. Below 60 sustained = chronic kidney disease.

Calcium — bone, nerve, muscle function. Elevated calcium warrants a workup (parathyroid, vitamin D, malignancy).

Liver enzymes (ALT, AST, ALP) — liver injury markers, not liver function per se. Mildly elevated ALT/AST is most often fatty liver disease — the most common liver issue in adults today.

Albumin and total protein — synthesis and nutrition. Low albumin can indicate liver dysfunction, chronic inflammation, or significant nutritional deficit.

Bilirubin — liver clearance. Mildly elevated indirect bilirubin in an otherwise healthy person is often Gilbert's syndrome — benign.

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Lipid panel — and why standard cholesterol underreports

Standard panel: total cholesterol, LDL, HDL, triglycerides.

Total cholesterol is the least informative number. Stop anchoring on it.

LDL — traditionally "bad cholesterol." Strong driver of atherosclerotic cardiovascular disease.

HDL — traditionally "good cholesterol." Higher generally better; the relationship is non-linear, and very high HDL isn't necessarily protective.

Triglycerides — marker of metabolic health. Elevated triglycerides + low HDL is the classic insulin-resistance signature.

Triglyceride/HDL ratio — quick proxy for insulin resistance. Above 3 is concerning; under 1.5 is reassuring.

What's missing from a standard lipid panel

ApoB — the actual number of atherogenic particles. Two patients with the same LDL can have very different ApoB and very different risk. ApoB is the better target.

Lp(a) — genetically determined, lifelong risk factor for cardiovascular disease. Check it once. If it's elevated, you adjust everything else more aggressively.

If your only cardiovascular risk lab is a standard panel, you're using 1990s tools.

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On "normal range"

Reference ranges are built from a statistical sampling of the lab's patient population. Two implications:

• "Normal" is a population descriptor, not "optimal for you."
• Many ranges drift as the population gets less healthy. TSH and vitamin D are good examples — the lower bounds of normal are not the same as therapeutic targets.

When I read your labs, I'm not just asking "is it in range" — I'm asking "is this number consistent with what your body should look like," and "is it trending the wrong direction even within range."

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What to actually do

• Get your annual labs.
• Get a copy. Build a folder.
• Add ApoB and Lp(a) at least once.
• If something is abnormal, get it explained — not just "I'll watch it."

A real reading of your basic labs takes a clinician about 15 minutes. If yours have never been read that way, that's worth asking for.