CBC and CMP lab panels are common screening tests used to evaluate blood cells, electrolytes, kidney function, liver function, glucose, and protein status. This cheat sheet helps students connect lab names, normal adult reference ranges, and possible meanings of abnormal results. It is meant for learning patterns, not for diagnosing disease.
Reference ranges can vary by lab, age, sex, pregnancy status, and clinical context.
A CBC focuses on red blood cells, white blood cells, platelets, hemoglobin, hematocrit, and red blood cell indices. A CMP includes glucose, electrolytes, kidney markers, liver markers, bilirubin, albumin, total protein, and calcium. Useful interpretation often compares related values, such as BUN with creatinine or AST with ALT.
Always interpret results with symptoms, history, medications, hydration status, and the ordering clinician's guidance.
Key Facts
- CBC stands for complete blood count and commonly includes WBC, RBC, hemoglobin, hematocrit, platelets, MCV, MCH, MCHC, and RDW.
- Typical adult WBC range is about 4.0 to 11.0 x 10^3 cells/uL, and high WBC can suggest infection, inflammation, stress, or some blood disorders.
- Typical adult hemoglobin is about 13.5 to 17.5 g/dL in males and 12.0 to 15.5 g/dL in females, and low hemoglobin suggests anemia or blood loss.
- Hematocrit is the percent of blood volume made of red blood cells, with typical adult ranges of about 41% to 53% in males and 36% to 46% in females.
- MCV is mean corpuscular volume, and MCV less than 80 fL suggests microcytic red cells while MCV greater than 100 fL suggests macrocytic red cells.
- CMP electrolytes include sodium, potassium, chloride, and CO2, with common adult ranges of Na 135 to 145 mEq/L, K 3.5 to 5.0 mEq/L, Cl 98 to 106 mEq/L, and CO2 22 to 29 mEq/L.
- Kidney markers on a CMP include BUN and creatinine, with typical adult ranges of BUN 7 to 20 mg/dL and creatinine about 0.6 to 1.3 mg/dL.
- Liver-related CMP values include AST, ALT, alkaline phosphatase, bilirubin, albumin, and total protein, and patterns across these markers are more useful than one isolated value.
Vocabulary
- CBC
- A complete blood count is a lab panel that measures blood cells, including red blood cells, white blood cells, and platelets.
- CMP
- A comprehensive metabolic panel is a lab panel that measures electrolytes, glucose, kidney markers, liver markers, proteins, and calcium.
- Hemoglobin
- Hemoglobin is the oxygen-carrying protein inside red blood cells, reported in grams per deciliter.
- Hematocrit
- Hematocrit is the percentage of blood volume made up of red blood cells.
- Creatinine
- Creatinine is a waste product from muscle metabolism that is commonly used to estimate kidney filtration function.
- Reference range
- A reference range is the set of values expected for many healthy people, but it may vary by laboratory and patient factors.
Common Mistakes to Avoid
- Treating one abnormal value as a diagnosis is wrong because lab results must be interpreted with symptoms, history, medications, and related lab values.
- Ignoring the lab's own reference range is wrong because normal ranges can differ by testing method, age, sex, pregnancy status, and local standards.
- Confusing hemoglobin with hematocrit is wrong because hemoglobin measures oxygen-carrying protein while hematocrit measures the percent of blood volume made of red cells.
- Assuming high BUN always means kidney failure is wrong because dehydration, high protein intake, bleeding in the digestive tract, and medications can also raise BUN.
- Interpreting AST and ALT separately is wrong because liver injury patterns are better understood by comparing AST, ALT, alkaline phosphatase, bilirubin, and clinical context.
Practice Questions
- 1 A patient has WBC 14.2 x 10^3 cells/uL when the reference range is 4.0 to 11.0 x 10^3 cells/uL. Is this low, normal, or high, and what broad process might it suggest?
- 2 A CBC shows hemoglobin 10.2 g/dL and MCV 72 fL. Is the red blood cell size microcytic, normocytic, or macrocytic, and what general condition does the low hemoglobin suggest?
- 3 A CMP shows sodium 139 mEq/L, potassium 5.8 mEq/L, chloride 102 mEq/L, and CO2 24 mEq/L. Which electrolyte is outside the listed common range?
- 4 Why should a clinician compare related CMP values such as BUN, creatinine, electrolytes, AST, ALT, bilirubin, and albumin instead of interpreting each number in isolation?