Laboratory test results provide a biochemical snapshot of the body. Understanding the reference range is foundational, as this range represents expected values in a healthy population. A result outside this limit indicates a deviation that may warrant further investigation. These results are highly context-dependent, influenced by factors like diet, medication, and time of day. This guide demystifies routine lab panels, offering a general overview of what each reading measures. This information is for general knowledge only and should always be discussed with a qualified healthcare provider.
Decoding the Complete Blood Count (CBC)
The Complete Blood Count (CBC) is a routine panel assessing the three major cellular components in the blood: red cells, white cells, and platelets. The test screens for conditions like anemia, infection, and blood disorders. The CBC provides insights into the body’s oxygen-carrying capacity, immune status, and ability to clot blood.
White Blood Cells (WBC)
White Blood Cells (leukocytes) are the body’s primary defense against infection. The typical reference range is 4,500 to 11,000 cells per microliter. An elevated count (leukocytosis) commonly signals infection, inflammation, or a reaction to certain medications. High levels may also indicate leukemia or severe allergic reactions.
A lower-than-normal count (leukopenia) suggests problems with bone marrow production. This decrease can result from viral infections, autoimmune conditions, or exposure to chemotherapy or radiation, compromising the immune system.
Red Blood Cells (RBC) and Oxygen Capacity
Red Blood Cells (RBCs), Hemoglobin (Hgb), and Hematocrit (Hct) transport oxygen throughout the body. Hemoglobin is the iron-containing protein within RBCs. Hematocrit measures the percentage of blood volume occupied by RBCs.
Low levels of RBC, Hgb, or Hct indicate anemia, often caused by blood loss, nutritional deficiencies (iron or B12), or chronic diseases. Elevated levels (polycythemia or erythrocytosis) may result from dehydration, chronic low oxygen levels (e.g., lung disease), or a rare blood disorder.
Platelets
Platelets (thrombocytes) are cell fragments that stop bleeding (hemostasis). Their normal count is generally between 150,000 and 450,000 per microliter. When injury occurs, platelets aggregate to form a plug and initiate clotting.
A high count (thrombocytosis) may react to infection, inflammation, or malignancy, increasing the risk of abnormal clotting. A low count (thrombocytopenia) can result from bone marrow suppression or autoimmune destruction, increasing the risk of excessive bleeding and bruising.
Essential Metabolic and Electrolyte Indicators
The Basic Metabolic Panel (BMP) assesses the body’s metabolic status, focusing on energy supply and the balance of fluids and electrolytes (electrically charged minerals). These indicators provide information about kidney function, blood sugar regulation, and acid-base balance.
Glucose (Blood Sugar)
Glucose is the body’s main energy source, regulated by hormones like insulin. A normal fasting reading is typically between 70 and 100 mg/dL. Persistent elevation (hyperglycemia) suggests prediabetes (100–125 mg/dL) or diabetes (126 mg/dL or higher). Unmanaged hyperglycemia can lead to long-term nerve and organ damage.
Low blood glucose (hypoglycemia) is generally below 70 mg/dL. Hypoglycemia causes acute symptoms like confusion and dizziness, and may indicate liver or kidney disease.
Sodium (Na)
Sodium is the most abundant extracellular electrolyte, regulating fluid balance and nerve and muscle function. The reference range is typically 135 to 145 mEq/L. Low sodium (hyponatremia) often occurs with excessive water retention, such as in heart or liver failure. Symptoms range from mild confusion to severe seizures.
High sodium (hypernatremia) usually results from dehydration. Hypernatremia can cause restlessness, confusion, and seizures due to rapid fluid shifts in the brain.
Potassium (K)
Potassium is the main positively charged ion inside cells, important for heart rhythm and muscle contraction. The normal serum range is narrow, typically 3.5 to 5.0 mEq/L. Low potassium (hypokalemia) is often caused by increased loss through the kidneys or GI tract (e.g., due to diuretics, vomiting, or diarrhea).
Hypokalemia can cause muscle weakness and irregular heart rhythms. High potassium (hyperkalemia) is a concern in kidney failure, as the kidneys cannot excrete the mineral effectively. Severe hyperkalemia can dangerously slow the heart rate.
Chloride (Cl) and Bicarbonate/CO2
Chloride is the major negatively charged ion outside cells, working with sodium to maintain electrical neutrality and fluid balance. Its normal range is approximately 98 to 106 mEq/L. Chloride deviations often relate to sodium shifts or acid-base imbalances.
Bicarbonate (reported as CO2) is a primary buffer maintaining stable blood pH, with a normal range of 22 to 28 mEq/L. Low bicarbonate suggests metabolic acidosis (blood is too acidic), often causing rapid breathing. High bicarbonate suggests metabolic alkalosis (blood is too alkaline), which can result from prolonged vomiting or certain diuretics.
Assessing Organ Function and Waste Markers
This section examines markers reflecting the body’s ability to filter waste and process materials, focusing primarily on kidney and liver function. These tests measure metabolic end-products and enzymes released during tissue damage, helping assess organ stress or structural integrity.
Kidney Waste: BUN and Creatinine
The kidneys filter waste products, including Blood Urea Nitrogen (BUN) and Creatinine. BUN is a waste product of protein metabolism (normal range 7–20 mg/dL). Creatinine is a waste product from normal muscle breakdown (normal range 0.5–1.2 mg/dL).
Elevated levels of both indicate inefficient kidney filtering, suggesting injury or disease. BUN levels are sensitive to dehydration, high protein intake, or GI bleeding, which can elevate BUN without a primary kidney issue. Creatinine is more stable and its elevation is a more reliable indicator of impaired kidney clearance.
The BUN/Creatinine Ratio (normal 10:1 to 20:1) helps differentiate causes. A high ratio suggests a problem before the kidney, like severe dehydration. A low ratio can suggest malnutrition or advanced liver disease.
Liver Enzymes: AST and ALT
Liver health is assessed by measuring enzymes like Aspartate Aminotransferase (AST) and Alanine Aminotransferase (ALT). These enzymes are contained within liver cells and leak into the bloodstream when the cells are damaged. Normal ranges for both are typically low (5–40 U/L).
Elevation indicates hepatocellular injury (direct damage to liver cells), often from viral hepatitis, fatty liver disease, or medications. High AST, particularly when the AST to ALT ratio is 2:1 or greater, can suggest alcohol-related liver damage, as AST is also present in heart and muscle tissue.
Other Liver Markers: ALP and Bilirubin
Alkaline Phosphatase (ALP) is an enzyme found in the liver, bone, and intestines (normal range 30–120 IU/L). Elevated ALP can indicate liver problems, specifically a blockage in the bile ducts (cholestasis), as the enzyme is released when bile flow is impaired. High levels are also seen during rapid bone growth or in certain bone diseases.
Bilirubin is a yellowish compound created when red blood cells break down. The liver processes and excretes bilirubin in bile (normal total bilirubin is less than 1.0 mg/dL). Elevated bilirubin (hyperbilirubinemia) causes jaundice. This elevation occurs when liver cells are damaged or when bile ducts are blocked.
Understanding Lipid and Cardiovascular Risk Panels
The Lipid Panel measures different types of fats (lipids) in the blood to assess long-term cardiovascular disease risk. The balance of these fats predicts plaque buildup in the arteries. This panel focuses on chronic risk assessment.
Total Cholesterol
Total Cholesterol is the sum of all cholesterol types, representing the overall concentration of this waxy, fat-like substance. A desirable level is generally below 200 mg/dL. High total cholesterol, especially above 240 mg/dL, is associated with an increased risk of atherosclerosis (hardening and narrowing of the arteries).
Low-Density Lipoprotein (LDL)
Low-Density Lipoprotein (LDL) is often called “bad” cholesterol because it contributes to plaque formation in the arteries. The target for most healthy individuals is less than 100 mg/dL, though targets are lower for those with pre-existing heart disease. High LDL levels accelerate atherosclerosis, increasing the likelihood of heart attack and stroke. Lower concentrations indicate a reduced risk for plaque accumulation.
High-Density Lipoprotein (HDL)
High-Density Lipoprotein (HDL) is known as “good” cholesterol because it removes excess cholesterol from the arteries and transports it to the liver for disposal. A higher level of HDL is protective against heart disease. Desirable levels are 40 mg/dL or higher for men and 50 mg/dL or higher for women, with levels above 60 mg/dL considered optimal. Low HDL levels are a risk factor, suggesting inefficient cholesterol clearance. Lifestyle factors like physical activity can help raise HDL levels.
Triglycerides
Triglycerides are the most common type of fat in the body, storing excess energy from the diet. High levels are linked to increased heart disease risk and may indicate metabolic syndrome. A normal fasting level is less than 150 mg/dL.
Levels between 150 and 199 mg/dL are borderline high, and 200 mg/dL or more are considered high. Very high levels (exceeding 500 mg/dL) increase the risk of acute pancreatitis. Fasting for 9 to 12 hours before the test is typically required for an accurate reading.