Click image to open full size
Clinical Lab Values
CBC, CMP, ABG, Coagulation, Cardiac Markers
Related Tools
Related Worksheets
Clinical lab values help clinicians turn symptoms into measurable evidence about what is happening inside the body. A complete blood count, comprehensive metabolic panel, arterial blood gas, coagulation studies, and cardiac markers each reveal a different part of physiology. Together they help detect infection, anemia, electrolyte imbalance, acid base disorders, bleeding risk, organ injury, and myocardial damage. Learning the major patterns makes it easier to connect numbers to real disease processes.
These tests are most useful when interpreted in context rather than as isolated values. CBC reflects blood cell production and immune response, CMP surveys electrolytes and organ function, ABG shows ventilation and metabolic status, coagulation studies assess clotting pathways, and cardiac markers identify heart muscle injury. Students should focus on normal ranges, what direction of change means, and how multiple abnormalities fit together. Pattern recognition is especially important in emergencies such as sepsis, diabetic ketoacidosis, pulmonary failure, liver disease, and acute coronary syndrome.
Key Facts
- CBC includes WBC, hemoglobin, hematocrit, platelets, and red cell indices such as MCV.
- Anemia can be estimated by Hct approximately equal to 3 x Hgb, and MCV less than 80 fL suggests microcytic anemia.
- ABG interpretation starts with pH, where pH less than 7.35 indicates acidemia and pH greater than 7.45 indicates alkalemia.
- Henderson-Hasselbalch relationship: pH is proportional to HCO3-/PaCO2, so metabolic disorders change HCO3- and respiratory disorders change PaCO2.
- Coagulation studies: PT and INR assess the extrinsic pathway, while aPTT assesses the intrinsic pathway.
- Cardiac troponin I or T is the most specific routine marker for myocardial injury, while BNP rises in heart failure.
Vocabulary
- Hemoglobin
- Hemoglobin is the oxygen carrying protein in red blood cells and is used to assess anemia or blood loss.
- Creatinine
- Creatinine is a waste product filtered by the kidneys and is used as a marker of renal function.
- PaCO2
- PaCO2 is the partial pressure of carbon dioxide in arterial blood and reflects how well the lungs are ventilating.
- INR
- INR is a standardized measure of prothrombin time used to compare clotting function across laboratories.
- Troponin
- Troponin is a protein released into the blood when cardiac muscle cells are injured.
Common Mistakes to Avoid
- Memorizing single lab values without looking for patterns, because many diagnoses depend on combinations such as low pH with low HCO3- or chest pain with rising troponin.
- Confusing serum potassium with total body potassium, because a normal or high blood potassium can still occur when total body stores are depleted, especially in acid base disorders.
- Interpreting a normal early troponin as ruling out myocardial infarction, because troponin often rises over time and must be correlated with symptoms, ECG findings, and repeat testing.
- Mixing up PT and aPTT pathways, because PT and INR mainly reflect the extrinsic pathway while aPTT mainly reflects the intrinsic pathway.
Practice Questions
- 1 A patient has Hgb = 8 g/dL and MCV = 72 fL. Is the patient anemic, and is the anemia microcytic, normocytic, or macrocytic?
- 2 An ABG shows pH = 7.30, PaCO2 = 50 mmHg, and HCO3- = 24 mEq/L. Is this primarily respiratory acidosis, respiratory alkalosis, metabolic acidosis, or metabolic alkalosis?
- 3 A patient with chest pain has a normal CBC and CMP but a rising troponin on repeat testing. Explain why the cardiac marker is more clinically important here than the normal blood count and metabolic panel.