Editing Reduction of Risk Potential (section)

== Laboratory Values: Normal Ranges and Clinical Significance ==

=== Serum Electrolytes ===

;Sodium, 135 to 145 mEq/L
Sodium is primarily a water problem, not a salt problem. '''Hyponatremia''' (below 135) is seen with excess free water, syndrome of inappropriate antidiuretic hormone, heart failure, cirrhosis, adrenal insufficiency, thiazide diuretics, psychogenic polydipsia, and irrigation with hypotonic fluids. Findings progress from headache, nausea, and lethargy to confusion, seizures, and coma as cerebral edema develops. Nursing application: institute seizure precautions, monitor neurologic status hourly when the level is falling quickly, and correct slowly. Overly rapid correction of chronic hyponatremia risks osmotic demyelination. '''Hypernatremia''' (above 145) reflects water deficit or sodium excess from dehydration, insensible losses, fever, diabetes insipidus, tube feedings without free water, or hypertonic saline. Findings include thirst, dry sticky mucous membranes, restlessness, agitation, and twitching (Ignatavicius et al., 2021; Pagana et al., 2022).

;Potassium, 3.5 to 5.0 mEq/L
The most consequential electrolyte for cardiac safety. '''Hypokalemia''' arises from loop and thiazide diuretics, vomiting, nasogastric suction, diarrhea, insulin therapy, corticosteroids, and alkalosis. Findings include muscle weakness, leg cramps, decreased deep tendon reflexes, paralytic ileus with hypoactive or absent bowel sounds, and electrocardiogram changes of flattened T waves, ST depression, and a U wave. '''Hyperkalemia''' arises from renal failure, potassium-sparing diuretics, angiotensin converting enzyme inhibitors and angiotensin receptor blockers, crush injury, burns, tumor lysis, acidosis, and blood transfusion of older units. Findings include muscle weakness, paresthesias, and peaked T waves progressing to a widened QRS and cardiac arrest. Nursing application: intravenous potassium is '''never''' given by intravenous push or bolus and is not given intramuscularly. It must be diluted and infused by pump, generally not exceeding 10 mEq per hour on a general unit, with confirmation of adequate urine output before administration. Report a potassium above about 5.5 mEq/L or below about 3.0 mEq/L promptly, and check the level before giving digoxin (Ignatavicius et al., 2021; Pagana et al., 2022).

;Chloride, 98 to 106 mEq/L
Moves with sodium and shifts inversely with bicarbonate. Loss through vomiting or gastric suction contributes to metabolic alkalosis (Pagana et al., 2022).

;Total calcium, 9.0 to 10.5 mg/dL (ionized calcium approximately 4.5 to 5.6 mg/dL)
Total calcium is bound to albumin, so a low albumin falsely lowers the total calcium while the physiologically active ionized fraction is normal. '''Hypocalcemia''' follows thyroid or parathyroid surgery, acute pancreatitis, chronic kidney disease, vitamin D deficiency, massive transfusion with citrated blood, and alkalosis. Findings include perioral and digital numbness and tingling, muscle twitching, a positive Chvostek sign (facial twitch on tapping the facial nerve), a positive Trousseau sign (carpal spasm with blood pressure cuff inflation), tetany, and laryngospasm. Nursing application: after thyroidectomy or parathyroidectomy, keep intravenous calcium gluconate and emergency airway equipment available and assess for these signs on every shift. '''Hypercalcemia''' follows hyperparathyroidism, malignancy with bone metastases, prolonged immobilization, and excessive calcium or vitamin D intake. Findings include lethargy, confusion, constipation, decreased deep tendon reflexes, polyuria, and kidney stones (Harding et al., 2023; Pagana et al., 2022).

;Magnesium, 1.3 to 2.1 mEq/L (approximately 1.8 to 2.6 mg/dL)
'''Hypomagnesemia''' accompanies alcohol use disorder, malnutrition, diarrhea, and diuretic therapy, and it produces hyperexcitability, tremor, positive Chvostek and Trousseau signs, and dysrhythmias including torsades de pointes. Hypokalemia that will not correct is often a hidden magnesium deficiency. '''Hypermagnesemia''' occurs with renal failure and with magnesium sulfate therapy in obstetrics; the earliest reliable warning is loss of the patellar deep tendon reflex, followed by respiratory depression, hypotension, and cardiac arrest. Nursing application: during magnesium sulfate infusion, monitor deep tendon reflexes, respiratory rate, level of consciousness, and urine output, and keep calcium gluconate at the bedside as the antidote (Ignatavicius et al., 2021; Pagana et al., 2022).

;Phosphorus, 3.0 to 4.5 mg/dL
Varies inversely with calcium. Elevated in renal failure; low in refeeding syndrome, alcohol use disorder, and respiratory alkalosis (Pagana et al., 2022).

=== Renal Function and Fluid Status ===

;Blood urea nitrogen, 10 to 20 mg/dL
Rises with dehydration, high protein intake, gastrointestinal bleeding, catabolic states, corticosteroids, and renal impairment. Because it is influenced by hydration and protein load, it is a less specific marker of kidney function than creatinine (Pagana et al., 2022).

;Serum creatinine, approximately 0.6 to 1.2 mg/dL
The more specific indicator of glomerular filtration. A rise from 0.8 to 1.6 mg/dL is a doubling and represents a substantial loss of function even though both numbers look small. Nursing application: check creatinine and estimated glomerular filtration rate before nephrotoxic agents including intravenous contrast, aminoglycosides, vancomycin, amphotericin B, and nonsteroidal anti-inflammatory drugs (Harding et al., 2023; Pagana et al., 2022).

;Blood urea nitrogen to creatinine ratio, roughly 10:1 to 20:1
A disproportionately elevated ratio suggests a prerenal cause such as dehydration or hypovolemia rather than intrinsic kidney injury (Pagana et al., 2022).

;Serum osmolality, approximately 275 to 295 mOsm/kg
Rises with dehydration and hyperglycemia; falls with fluid overload and syndrome of inappropriate antidiuretic hormone (Pagana et al., 2022).

;Urine specific gravity, approximately 1.005 to 1.030
Concentrated urine above the range suggests dehydration or antidiuretic hormone excess; persistently dilute urine near 1.001 to 1.005 suggests diabetes insipidus, overhydration, or loss of concentrating ability (Pagana et al., 2022).

=== Hematology ===

;Hemoglobin, approximately 12 to 16 g/dL in females and 14 to 18 g/dL in males
;Hematocrit, approximately 37 to 47 percent in females and 42 to 52 percent in males
Hematocrit is roughly three times the hemoglobin. Both fall with bleeding, hemolysis, marrow suppression, and chronic kidney disease, and both rise with dehydration (a relative, not a true, increase) and with chronic hypoxemia. Nursing application: after any procedure with bleeding risk, a falling hemoglobin with rising heart rate and falling blood pressure is occult hemorrhage until proven otherwise (Ignatavicius et al., 2021; Pagana et al., 2022).

;White blood cells, approximately 5,000 to 10,000/mm3
Elevation suggests infection, inflammation, stress, or corticosteroid effect. Depression suggests marrow suppression from chemotherapy or radiation, overwhelming sepsis, or immune disorders. A left shift with increased immature bands signals acute bacterial infection. The absolute neutrophil count, not the total white count, determines infection risk; a count below 500/mm3 is severe neutropenia. Nursing application: neutropenic clients may mount no purulent drainage and no leukocytosis, so a low-grade fever may be the only sign of serious infection and warrants immediate reporting (Ignatavicius et al., 2021; Pagana et al., 2022).

;Platelets, approximately 150,000 to 400,000/mm3
Below roughly 50,000/mm3 raises bleeding risk with trauma or procedures, and below roughly 20,000/mm3 raises the risk of spontaneous bleeding. Nursing application: institute bleeding precautions, which include an electric razor, a soft toothbrush, no rectal temperatures or suppositories, no intramuscular injections when avoidable, prolonged pressure after venipuncture, and avoidance of aspirin and nonsteroidal anti-inflammatory drugs (Harding et al., 2023; Pagana et al., 2022).

=== Coagulation Studies ===

;Prothrombin time, approximately 11 to 12.5 seconds; international normalized ratio, approximately 0.8 to 1.1 untreated
Monitors '''warfarin''', which affects the extrinsic pathway and vitamin K dependent factors. Usual therapeutic international normalized ratio for atrial fibrillation and venous thromboembolism is about 2.0 to 3.0, and about 2.5 to 3.5 for many mechanical valves. Antidote: '''vitamin K (phytonadione)'''. Nursing application: teach consistent, not absent, dietary vitamin K intake, and review interacting drugs, especially antibiotics, amiodarone, and nonsteroidal anti-inflammatory drugs (Harding et al., 2023; Pagana et al., 2022).

;Activated partial thromboplastin time, approximately 30 to 40 seconds
Monitors '''unfractionated heparin''', which affects the intrinsic pathway. Therapeutic range is generally 1.5 to 2.5 times the control value. Antidote: '''protamine sulfate'''. Low molecular weight heparin such as enoxaparin does not require routine activated partial thromboplastin time monitoring. Nursing application: monitor the platelet count for heparin-induced thrombocytopenia, suspected when platelets drop substantially after several days of heparin, which paradoxically causes thrombosis; heparin must be stopped, and the client must not receive low molecular weight heparin as a substitute (Harding et al., 2023; Pagana et al., 2022).

;D-dimer
Elevated with active clot breakdown, as in pulmonary embolism, deep vein thrombosis, and disseminated intravascular coagulation. It is sensitive but not specific and rises with surgery, trauma, pregnancy, malignancy, and advanced age (Pagana et al., 2022).

=== Arterial Blood Gases ===

;pH 7.35 to 7.45, PaCO2 35 to 45 mm Hg, HCO3 22 to 26 mEq/L, PaO2 80 to 100 mm Hg, SaO2 95 to 100 percent
Interpretation sequence: look at the pH to decide acidemia or alkalemia, then decide whether the PaCO2 (respiratory) or the HCO3 (metabolic) moves in the direction that explains the pH, then judge compensation by whether the other value has also shifted and whether the pH has returned into range (Pagana et al., 2022).

* '''Respiratory acidosis''': low pH, high PaCO2. Hypoventilation from opioid oversedation, chronic obstructive pulmonary disease exacerbation, atelectasis, neuromuscular weakness, or airway obstruction.
* '''Respiratory alkalosis''': high pH, low PaCO2. Hyperventilation from anxiety, pain, fever, sepsis, early pulmonary embolism, or excessive mechanical ventilation.
* '''Metabolic acidosis''': low pH, low HCO3. Diabetic ketoacidosis, lactic acidosis from shock, renal failure, prolonged diarrhea, salicylate overdose. Expect compensatory deep rapid Kussmaul respirations.
* '''Metabolic alkalosis''': high pH, high HCO3. Prolonged vomiting, nasogastric suction, excessive antacid or bicarbonate intake, diuretic-induced potassium and chloride loss.

Nursing application: draw arterial specimens with attention to the Allen test for radial punctures, apply firm pressure for at least five minutes afterward and longer if the client is anticoagulated, and place the specimen on ice for transport if not analyzed immediately. In clients with chronic carbon dioxide retention, correlate the gas with the client's baseline rather than the textbook range (Ignatavicius et al., 2021; Potter et al., 2023).

=== Glucose and Metabolic Markers ===

;Fasting blood glucose, approximately 70 to 100 mg/dL
;Glycosylated hemoglobin (HbA1c), below 5.7 percent normal; a common treatment target in diabetes is below 7 percent
HbA1c reflects average glycemic control over roughly the preceding two to three months and is not affected by the client's breakfast. Nursing application: hypoglycemia below approximately 70 mg/dL presents with diaphoresis, tremor, tachycardia, hunger, and confusion, and is treated in the conscious client with 15 grams of a fast-acting carbohydrate, rechecked in 15 minutes. Beta blockers can mask the adrenergic warning signs, leaving diaphoresis as the main clue (American Diabetes Association Professional Practice Committee, 2024; Pagana et al., 2022).

;Cholesterol below 200 mg/dL, low density lipoprotein below 100 mg/dL, triglycerides below 150 mg/dL, high density lipoprotein above roughly 40 mg/dL in males and 50 mg/dL in females
Risk stratification for atherosclerotic disease; targets are individualized by overall cardiovascular risk (Pagana et al., 2022).

;Albumin, approximately 3.5 to 5.0 g/dL
A marker of prolonged nutritional and hepatic status. Low albumin predicts poor wound healing, edema from reduced oncotic pressure, and increased free fraction of protein-bound drugs such as phenytoin and warfarin (Pagana et al., 2022).

=== Cardiac Markers ===

;Troponin I and troponin T
The most sensitive and specific markers of myocardial injury. Threshold values are assay specific, so read the individual laboratory's cutoff; conventional troponin I is often reported as normal below roughly 0.04 ng/mL. Troponin rises within a few hours of infarction and stays elevated for days, making it useful for clients who present late. Serial specimens are drawn at defined intervals (Pagana et al., 2022).

;Creatine kinase MB
Rises and falls faster than troponin and is now largely supplementary (Pagana et al., 2022).

;B-type natriuretic peptide, generally below 100 pg/mL
Released with ventricular stretch. Useful to distinguish heart failure from pulmonary causes of dyspnea. Levels rise with age and renal impairment (Pagana et al., 2022).

=== Liver and Pancreatic Studies ===

;Alanine aminotransferase and aspartate aminotransferase
Roughly 4 to 36 units/L and 0 to 35 units/L in many laboratories; alanine aminotransferase is the more liver-specific of the two. Elevations occur with hepatitis, hepatotoxic drugs including acetaminophen, statins, isoniazid, and many antiretrovirals, and with alcohol-related injury (Pagana et al., 2022).

;Total bilirubin, approximately 0.3 to 1.0 mg/dL
Elevation produces jaundice, scleral icterus, dark urine, and pruritus (Pagana et al., 2022).

;Serum ammonia
Elevated in hepatic failure and correlated with encephalopathy. Lactulose is titrated to produce two to three soft stools per day, and improving mental status is the key therapeutic endpoint (Harding et al., 2023; Pagana et al., 2022).

;Amylase and lipase
Both rise in acute pancreatitis; lipase is more specific and stays elevated longer (Pagana et al., 2022).

=== Therapeutic Drug Levels ===

;Digoxin, approximately 0.5 to 2.0 ng/mL, with many heart failure regimens targeting the lower end
Toxicity presents with anorexia, nausea and vomiting, visual disturbance including yellow-green halos, bradycardia, and dysrhythmias. Hypokalemia, hypomagnesemia, hypercalcemia, renal impairment, and advanced age all increase toxicity risk at a given serum level. Nursing application: count the apical pulse for a full minute and hold the dose for an adult rate below 60 beats per minute, following facility policy, then report (Ignatavicius et al., 2021; Pagana et al., 2022).

;Lithium, approximately 0.6 to 1.2 mEq/L maintenance; toxicity risk rises above about 1.5 mEq/L
Sodium and fluid loss from dehydration, vomiting, diarrhea, sweating, low sodium diets, and thiazide diuretics and nonsteroidal anti-inflammatory drugs raises lithium levels. Early toxicity brings nausea, diarrhea, fine tremor, and drowsiness; severe toxicity brings coarse tremor, ataxia, confusion, and seizures (Pagana et al., 2022).

;Phenytoin, approximately 10 to 20 mcg/mL
Toxicity presents with nystagmus, ataxia, slurred speech, and confusion. Gingival hyperplasia is a chronic effect requiring meticulous oral care. Intravenous phenytoin is compatible with normal saline, not dextrose, and is infused slowly because of hypotension and dysrhythmia risk (Pagana et al., 2022).

;Theophylline, approximately 10 to 20 mcg/mL
Toxicity presents with tachycardia, restlessness, nausea, and seizures (Pagana et al., 2022).

;Vancomycin trough, commonly 10 to 20 mcg/mL depending on indication
Draw the trough immediately before the next dose. Monitor renal function and hearing. Rapid infusion causes flushing of the face and upper body from histamine release, which is an infusion-rate reaction rather than a true allergy, and is managed by slowing the infusion (Harding et al., 2023; Pagana et al., 2022).

;Aminoglycosides such as gentamicin
Nephrotoxic and ototoxic. Peak and trough monitoring plus creatinine surveillance is standard; report new tinnitus, vertigo, or hearing change (Pagana et al., 2022).