NCLEX-RN Flashcards: Lab Values, Normal Ranges, Critical Values, Nursing Actions

Critical lab values requiring immediate nursing action include potassium below 3.0 or above 6.0 milliequivalents per liter, sodium below 120 or above 160, glucose below 50 or above 400 milligrams per deciliter, hemoglobin below 7 grams per deciliter, platelet count below 50,000, INR above 4.0 for patients on warfarin, troponin above the upper reference limit, white blood cell count below 2,000 or above 30,000, and partial thromboplastin time above 100 seconds on heparin.

Normal hemoglobin for adult males is 14 to 18 grams per deciliter, and for adult females is 12 to 16 grams per deciliter. Normal hematocrit for males is 42 to 52 percent, and for females is 37 to 47 percent. Hematocrit is roughly three times the hemoglobin value. Low values indicate anemia from blood loss, iron deficiency, chronic disease, or bone marrow suppression. Elevated values occur in dehydration, polycythemia, and chronic hypoxia. In fluid volume deficit, both values are falsely elevated from hemoconcentration.

The normal white blood cell count is 4,500 to 11,000 cells per microliter. Leukocytosis, above 11,000, most commonly indicates bacterial infection, inflammation, stress, or corticosteroid use. Leukopenia, below 4,500, indicates bone marrow suppression from chemotherapy, radiation, or medications, immunodeficiency, or overwhelming infection. Neutropenia, specifically a neutrophil count below 1,500, places the patient at high risk for infection and requires protective isolation.

Blood urea nitrogen, or BUN, normally ranges from 10 to 20 milligrams per deciliter. Creatinine normally ranges from 0.7 to 1.3 milligrams per deciliter for men and 0.6 to 1.1 for women. Both are markers of kidney function. Elevated levels indicate decreased renal perfusion or kidney damage. BUN can also rise from dehydration, high protein diet, gastrointestinal bleeding, or corticosteroid use. Creatinine is a more specific indicator of kidney function because it is less affected by non-renal factors.

The therapeutic INR range for most patients on warfarin is 2.0 to 3.0, including those with atrial fibrillation, deep vein thrombosis, and pulmonary embolism. Patients with mechanical heart valves typically require a higher range of 2.5 to 3.5. An INR below the target indicates insufficient anticoagulation with increased clotting risk. An INR above the target indicates excessive anticoagulation with increased bleeding risk. Signs of over-anticoagulation include bruising, blood in urine or stool, prolonged bleeding from cuts, nosebleeds, and gum bleeding.

Elevated blood lactate, above 2 millimoles per liter, indicates tissue hypoxia and anaerobic metabolism. When cells do not receive adequate oxygen, they shift to anaerobic glycolysis, producing lactate as a byproduct. Common causes include sepsis, shock, severe heart failure, respiratory failure, and tissue ischemia. Lactate levels above 4 millimoles per liter are associated with high mortality and indicate a need for aggressive resuscitation. In sepsis, serial lactate measurements guide treatment adequacy. Decreasing lactate levels indicate improving tissue perfusion.

Key normal serum electrolyte ranges are sodium 136 to 145 milliequivalents per liter, potassium 3.5 to 5.0, chloride 98 to 106, bicarbonate 22 to 26, calcium 8.5 to 10.5 milligrams per deciliter, magnesium 1.5 to 2.5, and phosphorus 2.5 to 4.5 milligrams per deciliter. These values are frequently tested on the NCLEX. Calcium and phosphorus have an inverse relationship. Magnesium and potassium often move together, so hypomagnesemia makes hypokalemia difficult to correct. Electrolyte imbalances affect neuromuscular function, cardiac rhythm, and mental status.