Understanding Your Lab Results: A Patient's Guide

Updated March 28, 2026 • 11 min read • By National Healthcare Connect

Patient portals now deliver lab results directly to your phone, often before your doctor has reviewed them. Seeing a red flag on your results and waiting for a callback is stressful. Understanding what these tests measure — and what the numbers actually mean — helps you approach that conversation with your doctor far more productively.

How to Read a Lab Report

Most lab reports follow the same format:

• Test name: What was measured
• Your result: The measured value
• Reference range: The range considered normal for the lab's population. Values outside this range are often flagged with H (high) or L (low)
• Units: The measurement unit (mg/dL, g/dL, K/µL, etc.)

Reference ranges are statistical ranges — typically the range where 95% of a healthy population falls. This means 5% of perfectly healthy people will have at least one value outside the reference range on any given panel. A single out-of-range value in an otherwise normal panel, in a patient without symptoms, is often of minimal clinical concern.

Trends matter more than single values. A creatinine that was 0.9 last year and is now 1.3 (still within range) may be more meaningful than a one-time result of 1.5 with no prior comparison.

Complete Blood Count (CBC)

The CBC measures the cellular components of your blood. It is one of the most commonly ordered tests and screens for a wide range of conditions.

Key CBC Components

• WBC (White Blood Cell Count) — normal: 4.5–11.0 K/µL: White blood cells fight infection. High WBC (leukocytosis) may indicate infection, inflammation, or (rarely) leukemia. Low WBC (leukopenia) may occur with certain medications, viral infections, or bone marrow problems. A mildly elevated WBC in someone feeling sick is expected and not worrying.
• RBC (Red Blood Cell Count) and Hemoglobin / Hematocrit: These measure your red blood cell mass — the cells that carry oxygen. Low values indicate anemia. Hemoglobin normal ranges: men 13.5–17.5 g/dL; women 12.0–15.5 g/dL. Low hemoglobin triggers investigation into the cause: iron deficiency, B12/folate deficiency, chronic disease, or blood loss.
• MCV (Mean Corpuscular Volume) — normal: 80–100 fL: The average size of red blood cells. Small cells (low MCV = microcytic) often indicate iron deficiency. Large cells (high MCV = macrocytic) may indicate B12 or folate deficiency, or alcohol use. Very helpful in narrowing the cause of anemia.
• Platelets — normal: 150–400 K/µL: Platelets are essential for blood clotting. Low platelets (thrombocytopenia) increase bleeding risk. High platelets may indicate inflammation or reactive thrombocytosis. Severely low platelets (<50 K/µL) are a medical concern; mild decreases often need follow-up but not immediate intervention.
• Differential: Breaks down WBC into subtypes — neutrophils, lymphocytes, monocytes, eosinophils, basophils. High neutrophils suggest bacterial infection. High lymphocytes are typical with viral infections. High eosinophils may suggest allergies or parasitic infection.

Comprehensive Metabolic Panel (CMP)

The CMP (or Basic Metabolic Panel, BMP, for the shorter version) measures kidney function, liver function, electrolytes, and blood sugar. Typically ordered with annual physicals.

Kidney Function

• Creatinine (normal: ~0.6–1.2 mg/dL for men, 0.5–1.1 for women): A waste product filtered by kidneys. Elevated creatinine indicates reduced kidney function. Normal varies by muscle mass — very muscular people have naturally higher creatinine.
• BUN (Blood Urea Nitrogen, normal: 7–20 mg/dL): Another kidney waste marker. Often used alongside creatinine. Elevated BUN can reflect dehydration as well as kidney impairment.
• eGFR (estimated Glomerular Filtration Rate): Calculated from creatinine, age, and sex. Estimates kidney filtration capacity. Normal is >60 mL/min/1.73m²; below 60 on two separate tests indicates chronic kidney disease and warrants follow-up.

Liver Function Tests

• ALT and AST (normal: roughly 7–56 U/L for ALT; 10–40 U/L for AST): Liver enzymes. Elevated levels indicate liver cell damage or inflammation. Mildly elevated values often reflect fatty liver disease, recent alcohol use, or muscle injury (AST also comes from muscle). Markedly elevated values warrant further investigation.
• ALP (Alkaline Phosphatase): Can be elevated in liver or bone disease. Mildly elevated ALP is common and often not significant. It is also naturally elevated in children (growing bones) and pregnancy.
• Total Bilirubin (normal: 0.1–1.2 mg/dL): A breakdown product of red blood cells processed by the liver. High bilirubin can cause jaundice. Elevated bilirubin with other abnormal liver markers suggests liver disease; isolated mild elevation may be benign (Gilbert syndrome is a common harmless cause).
• Albumin (normal: 3.5–5.0 g/dL): The most abundant blood protein, made by the liver. Low albumin may indicate malnutrition, chronic liver disease, or kidney disease.

Electrolytes and Blood Sugar

• Sodium (normal: 135–145 mEq/L): Electrolyte essential for fluid balance and nerve function. Abnormalities can result from dehydration, overhydration, medications, or kidney problems.
• Potassium (normal: 3.5–5.0 mEq/L): Critical for heart and muscle function. Low potassium (hypokalemia) is common with diuretic use. High potassium (hyperkalemia) can be dangerous — requires follow-up if significantly elevated.
• Glucose (fasting normal: 70–99 mg/dL): Blood sugar. 100–125 mg/dL = prediabetes; 126+ mg/dL on two occasions = diabetes.
• Calcium (normal: 8.5–10.5 mg/dL): Involved in bone health, muscle contraction, and nerve function. Significantly high or low values warrant investigation.

Lipid Panel (Cholesterol)

• Total Cholesterol (desirable: <200 mg/dL): The sum of all cholesterol fractions. High total cholesterol alone is less meaningful than the breakdown.
• LDL ("bad" cholesterol, optimal: <100 mg/dL): The primary driver of cardiovascular risk. Lower is generally better. Your target LDL depends on your overall cardiovascular risk — people with prior heart attack or high-risk conditions have stricter targets (<70 mg/dL).
• HDL ("good" cholesterol, desirable: >60 mg/dL): Higher HDL is protective. HDL below 40 mg/dL in men or 50 mg/dL in women increases cardiovascular risk.
• Triglycerides (normal: <150 mg/dL): Blood fats closely linked to diet — high carbohydrate and alcohol intake raise triglycerides. Very high triglycerides (>500 mg/dL) increase pancreatitis risk.

HbA1c (Hemoglobin A1c)

HbA1c measures your average blood sugar over the past 2–3 months — it reflects how well blood sugar has been controlled, unlike a fasting glucose which is just a snapshot.

• Normal: below 5.7%
• Prediabetes: 5.7–6.4%
• Diabetes: 6.5% or higher (confirmed on a second test)
• Treatment target for most diabetics: below 7% (individualized based on age and risk factors)

Thyroid Function Tests

• TSH (Thyroid Stimulating Hormone, normal: ~0.4–4.0 mIU/L): The primary thyroid screening test. High TSH indicates the pituitary is working hard to stimulate a sluggish thyroid (hypothyroidism). Low TSH indicates overactive thyroid (hyperthyroidism). TSH is the most sensitive early indicator of thyroid dysfunction.
• Free T4 and Free T3: Actual thyroid hormones. Measured when TSH is abnormal to confirm the diagnosis and guide treatment. Low Free T4 with high TSH = confirmed hypothyroidism.

When to Call Your Doctor

Most portal results can wait for your next appointment or a routine follow-up message. Contact your doctor more urgently if you see:

• Potassium significantly above 5.5 mEq/L or below 3.0 mEq/L
• Sodium below 125 or above 155 mEq/L
• Hemoglobin below 8 g/dL
• Platelets below 50 K/µL
• Creatinine dramatically different from your baseline
• Any results your lab flags as "critical" with instructions to contact provider immediately

For anything else, document your questions and discuss at your next appointment. Seeing slightly abnormal values in isolation almost never requires immediate action.

This article is for informational purposes only and does not constitute medical advice. Lab results must be interpreted in clinical context by a qualified healthcare provider.