While you’ll ultimately learn a lot about lab values throughout nursing school, you won’t learn them all at once. To help you get started, I’ve compiled eight key lab values you should know thoroughly before your first clinical day: hemoglobin, hematocrit, WBCs, platelets, sodium, potassium, creatinine, and glucose. These are not the only labs you need to understand, but they will give you a solid foundation.

Hemoglobin

Hemoglobin is a protein in red blood cells that carries oxygen and carbon dioxide throughout the body. It’s a key component of the complete blood count (CBC) and reflects the number of RBCs in the blood.

While hemoglobin is often associated with anemia (low levels), it can also be elevated in conditions like polycythemia vera, COPD, certain cancers, pulmonary fibrosis, smoking, dehydration, high altitude, congenital heart disease, and the use of erythropoietin-stimulating agents.

Dehydration increases hemoglobin levels because it concentrates the blood. Conversely, increased plasma volume (such as in pregnancy) can lower hemoglobin levels. Conditions associated with low hemoglobin include anemia, cirrhosis, pregnancy, chronic kidney disease, bone marrow failure, splenomegaly, GI bleeds, and hemolytic reactions.

Hemoglobin levels guide blood transfusion decisions. A normal level is 12 to 18 g/dL, but transfusions are typically considered when levels drop below 7 or 8 g/dL in acute care settings. Each unit of blood transfused should raise hemoglobin by approximately 1 g/dL. A 2020 study showed no significant difference in hemoglobin levels when tested one hour, four hours, or 24 hours post-transfusion.

Patients with high hemoglobin may experience headache, hypertension, blurred vision, and fatigue. Severely elevated levels can cause ischemic events like stroke. Low hemoglobin can cause fatigue, weak pulses, cool extremities, pale skin, shortness of breath, lightheadedness, and chest pain. Patients with symptomatic low hemoglobin should remain on bed rest until it’s safe to increase activity, usually after their hemoglobin levels rise.

Hematocrit

Hematocrit measures the percentage of blood volume made up of red blood cells. It’s usually about three times the hemoglobin level and is also affected by plasma volume. Hematocrit increases by 3% with each unit of packed red blood cells transfused.

Pro Tip: When someone refers to the “H & H,” they’re talking about hemoglobin and hematocrit.

WBCs

The white blood cell (WBC) count is another important part of the CBC, especially for monitoring infection. Normal WBC count is about 5,000 to 10,000 in adults.

Leukocytosis (high WBC count) generally indicates infection but can also result from inflammation, trauma, stress, smoking, and certain medications like corticosteroids and lithium. Elevated WBCs are common in late pregnancy and labor and can also indicate cancers like acute myeloid leukemia.

A WBC differential test breaks down the types of WBCs, with increased bands (a type of neutrophil) indicating acute bacterial infection. Leukopenia (low WBC count) can occur in severe infection, bone marrow failure, autoimmune diseases, malnutrition, and due to

certain medications such as immunosuppressants, clozapine, hydroxychloroquine, lamotrigine, diuretics, and chemotherapeutic agents. Patients with very low WBC counts, especially low neutrophil counts, may be placed on neutropenic precautions to minimize infection risk. This includes thorough handwashing, wearing full PPE, and often keeping the room under positive pressure airflow.

Platelets

Platelet levels, part of the CBC, are crucial for blood clotting. Thrombocytopenia (low platelet count) increases bleeding risk, particularly if the count falls below 20,000. Causes include chemotherapy, leukemia, bone marrow failure, DIC, viral infections, lupus, and nutritional deficiencies. Immune thrombocytopenic purpura (ITP) is an autoimmune condition that can also cause low platelets.

Thrombocytosis (high platelet count) can result from conditions like polycythemia vera, malignancies, splenectomy, hemolytic anemia, inflammatory disorders like rheumatoid arthritis, and iron deficiency anemia. Elevated platelets can also occur with blood loss as the body attempts to stop bleeding.

Sodium

Sodium levels are closely tied to fluid balance and are regulated by hormones like aldosterone and antidiuretic hormone. Normal serum sodium levels are 135-145 mEq/L. Hyponatremia (low sodium) is common in clinical settings and can cause cerebral edema and neurological issues due to fluid shifts. Causes include excess water intake, decreased sodium intake, Addison’s disease, GI losses, hyperglycemia, and third-spacing of fluids.

Mild hyponatremia is treated by restricting free water intake, while severe cases might require hypertonic saline, administered slowly to avoid complications like central pontine myelinolysis.

Hypernatremia (high sodium) is often due to water losses (e.g., diabetes insipidus, burns) or increased sodium reabsorption (e.g., hyperaldosteronism, Cushing’s syndrome). Rapidly correcting hypernatremia can cause cerebral edema and seizures, so treatment is gradual, involving increased fluid intake or IV fluids.

Potassium

Potassium is critical for cardiac function, with normal serum levels between 3.5-5.0 mEq/L. Both hypo- and hyperkalemia can cause serious cardiac dysrhythmias and cardiac arrest. Hypokalemia risks include patients on loop diuretics, requiring careful monitoring and appropriate supplementation.

Hypokalemia signs include muscle weakness, gastric ileus, and depressed cardiac function, often initially presenting as PVCs. IV potassium is never given as a push due to the risk of cardiac arrest; it’s administered slowly and diluted.

Hyperkalemia can result from excessive intake, renal failure, hemolysis, and acidosis. It can cause tall, peaked T waves on an EKG, irritability, diarrhea, and vomiting. Treatment varies but can include kayexalate, insulin with dextrose, calcium IV to stabilize cardiac cells, and in severe cases, emergency dialysis.

Creatinine

Creatinine, part of the BMP or CMP, indicates kidney function. Elevated levels suggest impaired renal function or failure, caused by chronic kidney disease, acute conditions, nephrotoxic medications, or dehydration. Elevated creatinine necessitates adjustments in medication dosing and monitoring for complications like hyperkalemia and fluid overload.

Glucose

Monitoring glucose levels, found in BMP, CMP, or via POC testing, is crucial even for non-diabetic patients. Hypoglycemia can result from decreased nutritional intake and medications, requiring prompt correction to avoid neurological damage.

Hyperglycemia, common in stress situations like trauma or infection, needs careful management due to risks like infection, poor wound healing, and poor outcomes. Medications like corticosteroids and tricyclic antidepressants can also cause elevated glucose levels, necessitating timely intervention to ensure patient safety.

Understanding these eight key lab values will provide a strong foundation for your clinical practice and help you make informed decisions in patient care.