NCLEX-RN: Laboratory Tests

Laboratory Tests: Serum electrolyte levels

Focus topic: Laboratory Tests

Laboratory Tests: Potassium

A. Normal adult range 3.5–5.0 mEq/L. Child range 3.5–5.0 mEq/L. Critical values: Adults > 16 years < 2.8 mEq/L > 6.2 mEq/L. Pediatric (0–15 years) < 3.0 mEq/L > 6.5 mEq/L.

B. Purpose—Evaluates potassium levels that aids in diagnosing disorders such as acidosis, renal failure, and dehydration. Used to monitor the effectiveness of therapeutic interventions implemented.

C. Indications.

  •  Increased potassium K+—acute renal disease, burns, crushing injuries, adrenal insufficiency, dehydration, anorexia nervosa, excessive intake caused by specific drugs (potassium penicillin), salt substitute, or, the most common, too rapid infusion of intravenous (IV) solution containing potassium.
  • Decreased K+ renal loss (due to diuretics), loss from the gastrointestinal (GI) tract via nasogastric (NG) tube, vomiting or diarrhea, reduced potassium intake, hypomagnesemia, endocrine causes.

D. Treatment implications.

  •  Critical values may lead to fatal cardiac arrhythmias.
  •  Assess for signs and symptoms of potassium excess or loss (see below).

ROUTINE BLOOD CHEMISTRY TESTS*

Focus topic: Laboratory Tests

Laboratory Tests

E. Hyperkalemia.

  •  Removal of excess potassium per physician’s orders.
    a. Administer diuretics if kidney function is adequate.
    b. Administer exchange resins through NG tube or via sodium Kayexalate (polystyrene sulfonate) enema.
    c. Administer hypertonic IV glucose with insulin as ordered—moves potassium back into cells.
    d. Administer sodium bicarbonate—shifts potassium back into cells.
    e. Hemodialysis or peritoneal dialysis.
  •  Nursing considerations.
    a. Restrict potassium intake.
    b. Calcium will counteract negative effects of potassium on the heart.
    c. Frequently check cardiac monitor placed on client with hyperkalemia.
    d. Penicillin in form of potassium should not be administered to clients with hyperkalemia.

F. Hypokalemia.

  • Replacement of lost potassium.
    a. Administer oral potassium, monitor IV infusion of potassium.
    b. Replace no more than 20 mEq of KCl (potassium chloride) in 1 hour.
  •  Nursing considerations.
    a. Observe electrocardiogram (ECG) monitor if possible to observe for cardiac effect of KCl.
    b. Give foods rich in potassium—bananas, molasses, oranges, raisins, seafood.
    c. Assess for hypokalemia in clients who require frequent NG suctioning.

Laboratory Tests: Sodium

Focus topic: Laboratory Tests

A. Normal adult range 135–145 mEq/L. Child range 135–145 mEq/L. Critical values: Sodium < 120 mEq/L > 160 mEq/L.

B. Purpose—test for deficiency or excess of electrolyte seen in some endocrine disorders and monitor fluid balance in IV electrolyte therapy.

C. Indications.

  •  Increased level is a very high concentration of sodium in the extracellular fluid dehydration,severe vomiting or diarrhea, decreased water intake, fever, renal failure, and ingestion of sodium chloride (NaCl).
  • Decreased level is a very low concentration of sodium in the extracellular fluid diuretics, excessive perspiration, GI loss (vomiting, diarrhea), lack of sodium in diet, Addison’s disease or adrenal insufficiency, burns, and excessive IV solutions without NaCl replacement.

D. Treatment implications.

  •  Assess for signs and symptoms of sodium excess or loss.
  •  Assess for critical levels (< 120 mEq/L or > 155 mEq/L).

E. Hypernatremia.

  •  Removal of excess sodium.
    a. Administer salt-free IV solutions (dextrose), monitor for hyponatremia, and administer 0.45% NaCl to prevent hyponatremia.
    b. Restrict sodium in diet.
    c. Discontinue drugs that cause sodium retention.
  •  Nursing considerations.
    a. Weigh daily and record intake and output (I&O).
    b. Assess blood pressure level in terms of fluid retention.

F. Hyponatremia.

  • Replacement of lost sodium.
    a. Administer IV fluids with sodium (3% or B 5% saline) monitor venous pressure to prevent circulatory overload.
    b. Restrict water intake monitor intake and output.
  •  Nursing considerations.
    a. Clients who excrete excess sodium must be advised how to increase sodium intake.
    b. Assist client to identify symptoms of sodium depletion.

Laboratory Tests: Calcium

Focus topic: Laboratory Tests

A. Total serum level is 8.4–10.5 mEq/dL. Critical values: Calcium < 6.0 mg/dL > 13.0 mg/dL.

B. Purpose test for deficit or excess of calcium electrolyte.

C. Indications.

  •  Increased level excess of calcium in the extracellular fluid. Excess of vitamin D (from milk), hyperparathyroidism, cancer (neoplasm of parathyroid, multiple myeloma), immobilization, Paget’s disease, thyrotoxicosis, acromegaly, specific drugs (thiazide diuretics), and calcium supplements with inadequate assimilation.
  •  Decreased level deficit of calcium in the extracellular fluid. Vitamin D deficiency, magnesium deficiency, excessive laxatives, malabsorption syndrome, hypothyroidism, chronic renal insufficiency, burns, acute pancreatitis, removal of the parathyroid glands, blood transfusions (over 2000 mL) without calcium supplements, and specific drugs (anti-convulsant therapy).

D. Treatment implications.

  •  Assess for signs and symptoms of excess or loss of calcium.
  • Assess for critical levels of calcium (< 7.0 or > 13.5 mg/100 mL). Notify physician immediately.
    a. Assess for tetany and convulsions indicating hypocalcemia.
    b. Excess calcium may lead to coma.

E. Hypercalcemia.

  •  Removal of excess calcium.
    a. Increase fluid intake, which decreases tubular reabsorption of calcium and prevents stone formation.
    b. Promote calcium excretion (sodium salts IV and diuretics).
  •  Nursing considerations.
    a. Limit dietary intake of calcium.
    b. Avoid milk and milk products, which contain high levels of calcium.

F. Hypocalcemia.

  •  Replacement of low levels of calcium.
    a. Administer calcium gluconate IV or serum albumin if low levels are due to low serum albumin concentration.
    b. Monitor for tetany major symptom of hypocalcemia.
  •  Nursing considerations.
    a. Monitor by checking for positive Trousseau’s test or Chvostek’s sign.
    b. Administer oral calcium supplements and a diet high in calcium (dairy products, bone meal, molasses, yogurt) with vitamin D. Instruct client to take supplements before bed with vitamin C for greater absorption.

Laboratory Tests: Magnesium

Focus topic: Laboratory Tests

A. Normal serum level is 1.5–2.5 mEq/L. Critical values: Magnesium < 1.0 mg/dL > 4.7 mg/dL.

B. Purpose test for excess or deficit serum levels of magnesium to evaluate kidney function and metabolic disorders.

C. Indications.

  • Increased magnesium—renal insufficiency, severe dehydration, adrenal insufficiency,hypothyroidism, leukemia, overuse of antacids with magnesium (Gelusil), specific drugs.
  •  Decreased magnesium—acute pancreatitis, chronic nephritis, diuretic phase of renal failure, gastric drainage, abnormal loss due to diarrhea, impaired absorption, specific drugs (diuretics), hypercalcemia, acute alcoholism and cirrhosis, prolonged IV (3 weeks) without magnesium.

D. Treatment implications.

  •  Assess for signs and symptoms of magnesium excess or loss.
  •  Assess for critical values indicating immediate interventions.
    a. Increased level—above 2.5 mEq/L. The higher the level of magnesium, the more sedative the effect.
    b. Assess for loss of deep tendon reflexes, respiratory decrease, and cardiac arrest.

E. Hypermagnesemia.

  •  Removal of excess magnesium.
    a. Increase fluid intake for magnesium intoxication, give IV calcium gluconate slowly in peripheral veins (do not use a central venous pressure [CVP] line) to promote excretion of excess magnesium.
    b. Administer diuretics with possible renal dialysis if renal function is impaired.
  • Nursing considerations.
    a. Monitor for increased levels, which potentiate cardiac effect of increased potassium.
    b. Monitor for renal failure, often associated  with high levels of magnesium.

F. Hypomagnesemia.

  •  Replacement of magnesium.
    a. Assess for severe deficiency muscle twitching indicates neurological signs; nausea and vomiting indicate GI signs.
    b. Administer magnesium sulfate IV (10–40 mEq/L in IV fluid) or intramuscular (IM) slowly. Observe for urine output and keep antidote (calcium gluconate) available.
  •  Nursing considerations.
    a. Monitor daily ingestion of magnesium PO and promote diet high in magnesium— nuts, green vegetables, seafood.
    b. Check for hidden conditions affecting magnesium levels such as alcoholism, GI malabsorption.

Laboratory Tests: Chloride

Focus topic: Laboratory Tests

A. Normal serum value is 100–106 mEq/L.

B. Purpose test for excess or deficit levels.

C. Indications.

  •  Increased chloride—prolonged diarrhea leading to metabolic acidosis, acute renal failure, respiratory alkalosis (hyperventilation, central nervous system [CNS] damage), diabetes insipidus, dehydration, specific drugs (salicylate intoxication, steroids).
  •  Decreased chloride—prolonged vomiting or NG suction, loss of HCl (hydrogen chloride), diarrhea, metabolic acidosis, adrenocortical insufficiency, renal disease that loses salt, specific drugs.

D. Treatment implications.

  •  Assess for signs and symptoms of chloride excess and loss.
  • Assess for critical values, below 70 mEq/L or above 120 mEq/L.
  • Assess for conditions that cause increased sodium levels—may also cause increased chloride.E. Nursing considerations.

E. Nursing considerations.

  •  Record intake and output and daily weights to monitor electrolyte imbalances.
  •  Prolonged vomiting or uncontrollable diabetes  may lead to abnormally low levels of chloride.

Laboratory Tests: Phosphorus

Focus topic: Laboratory Tests

A. Normal serum value is 2.3–4.7 mg/dL. Phosphorus (inorganic) < 1.0 mg/dL*.

B. Purpose test for excess or deficit levels.

C. Indications.

  • Increased phosphorus—hypocalcemia, tetany, hypoparathyroidism, headaches, GI irritation, kidney disease, specific drugs, and vitamin D excess.
  •  Decreased phosphorus—hypocalcemia, hypomagnesemia, hyperparathyroidism, vitamin D deficiency, alcohol intoxication, malabsorption.

D. Treatment implications.

  •  Assess for signs and symptoms of phosphorus excess and loss.
  • Assess for critical values hyperphosphatemia may occur with hypocalcemia and cardiac complications (arrhythmias).

E. Nursing considerations.

  •  Hyperphosphatemia.
    a. May require dialysis to lower serum phosphorus.
    b. Gastric lavage with potassium may lower level of phosphorus.
    c. Blood transfusions may be necessary.
  •  Hypophosphatemia.
    a. Administer phosphate salt tablets or foods high in phosphorus (eggs, fish, meat, poultry, grains, peas, peanuts, walnuts, whole wheat, rye, and chocolate).
    b. Administer IV potassium phosphate.

Laboratory Tests: Chem 7

Focus topic: Laboratory Tests

A. Measure serum levels of seven substances: electrolytes (potassium, sodium, and chloride), carbon dioxide, glucose, blood urea nitrogen (BUN), and creatinine.

  • Tests fluid balance and renal function, as well as acid–base status.
  •  When combined with complete blood counts (CBC), these tests give a view of how the entire body is functioning.
  •  Chem 7 is also part of the preoperative workup.

Standard values of Chem 7 (may vary from lab to lab; check your own facility values).
a. Potassium: 3.5–5.3 mEq/L.
b. Sodium: 135–145 mEq/L.
c. Chloride: 98–106 mEq/L.
d. CO2: 23–30 mmol/L.
e. Glucose (fasting): 65–110 mg/dL.
f. BUN: 7–18 mg/dL.
g. Creatinine: 0.5–1.5 mg/dL.

B. How these values may be interpreted.

  •  Potassium: an electrolyte that helps maintain acid–base balance.
  •  Sodium: an electrolyte that helps maintain acid–base balance and osmotic pressure.
  •  Chloride: an electrolyte that helps maintain extra electrical neutrality; combines with sodium to form a salt.
  •  CO2: reflects value of bicarbonate in arterial blood.
  • Glucose: fasting blood glucose levels may identify diabetes.
  •  BUN: reflects liver’s ability to make urea and the kidney’s ability to excrete it. With renal disease, the BUN goes up.

Laboratory Tests: Cardiac Function Tests

Focus topic: Laboratory Tests

Laboratory Tests: Serum Cardiac Markers

Focus topic: Laboratory Tests

A. Enzyme activity evaluation denotes heart muscle
damage.

  • When the heart muscle is without oxygen for 30–60 minutes, the cells are damaged, which results in necrosis. Intracellular enzymes leak out of cell membranes and are released into the bloodstream as the cells die.
  •  Specific enzymes are released into the bloodstream at varying intervals; as myocardial cells die, they release chemicals that can be measured. The times of detection in the bloodstream, peak levels, and return to normal time vary greatly. a.Creatinine kinase (CK), formerly called creatinine phosphokinase (CPK)-isoenzymes (CPK-MB) most valuable measurement; level rises within 4–6 hours of initial heart muscle damage, peaking at 18–24 hours. More than 6 times normal value with damage—returns to normal within 3–4 days.
    b. Compare CK-MB with following two tests (serum glutamic oxaloacetic transaminase [SGOT] and lactate dehydrogenase [LDH]) to determine myocardial damage.
    c. Lactate dehydrogenase LDH1, LDH2- iso enzymes level rises in 12–24–48 hours; persists longer, can be as long as 2 weeks. When the physician analyzes these two levels (LDH1 and LDH2), he or she will look for a flipped ratio when LDH is the highest, it indicates a myocardial infarction (MI).
    d. SGOT+ or aspartate aminotransferase (AST). High levels peak following an acute MI or liver damage.
  •  CK-MB: one of three isoenzymes that make up the total creatinine kinase (CK).
    a. Diagnostically cardiac specific.
    b. Present in bloodstream within 3–8 hours.
    c. Peaks within 24 hours.
    d. Returns to normal within 48–72 hours.
  • Normal cardiac enzyme ranges.
    a. Total creatinine kinase—15–99 units/L; CK-MB, 0–6% heart value.
    b. Total lactate dehydrogenase—either 100– 190 units/L or 48–95 units/L; iso enzymes LDH1, 14–26% and LDH2, 27–37%.
    c. The greater the peak in enzymes and the longer the level remains, the more serious the heart damage.

B. Troponin test.

  •  Tested for myocardial injury; when infarction occurs, this substance is released in the bloodstream.
  •  Made up of three proteins found in striated muscle. Cardiac troponin T rises in 3–6 hours and remains up for 14–21 days; troponin 1 rises in 7–14 hours and remains up 5–7 days.Both are accurate assessments for myocardial damage.
  •  Normally values are low (troponin T 0.0–0.2 ng/mL and troponin 1 less than 0.6 ng/mL); any rise may indicate myocardial cell damage. Serial tests are important.

C. Myoglobin test.

  •  Oxygen-binding protein found in cardiac muscle (and skeletal muscle).
  • Level rises shortly after cell dies; peaks in 4–6 hours and returns to normal in 24–36 hours.

Laboratory Tests: B-Type Natriuretic Peptide

Focus topic: Laboratory Tests

BNP—NT-proBNP (B-type natriuretic peptide; brain natriuretic peptide).

A. BNP is a hormone released from the ventricles in response to increased wall tension (stress) that occurs with heart failure.

B. A baseline BNP may be helpful in the diagnosis of acute congestive heart failure (CHF) and a repeat BNP at discharge may be helpful in management on an ambulatory basis.

C. BNP levels rise as wall stress increases and are useful in the rapid evaluation of heart failure.

D. In general, the higher the BNP levels, the worse the heart failure. BNP can identify clients at a higher risk for death, independent of kidney dysfunction.

E. Purpose: To assess for heart failure. Normal values: < 50 yrs: 0–450 pg/mL. 50–75 yrs: 0–900 pg/mL. > 75 yrs: 0–1800 pg/mL.

 

Laboratory Tests: Blood Lipid Tests

Focus topic: Laboratory Tests

A. Normal values.

  •  Cholesterol—below 200 mg/100 mL is desirable (teenager’s level should be below 180 mg/100 mL). Levels over 239 mg/100 mL classified as high.
  •  Triglycerides—cluster of fatty acids formed from breakdown of dietary fat and simple sugar (40–150 mg/100 mL).
  •  Low-density lipoproteins (LDLs, the “bad” cholesterol)—60–180 mg/100 mL.
    a. LDLs burrow into the arterial walls to form plaque.
    b. Factors that lead to elevated LDL: diet (saturated fat and cholesterol); obesity; poorly controlled diabetes; genetic predisposition.
  •  Very-low-density lipoproteins (VLDLs)—25–50% of total cholesterol.
  • High-density lipoproteins (HDLs, the “good” cholesterol) male level, 30–70 mg/100 mL; female level, 30–80 mg/100 mL.
  •  The “ideal” lipoprotein profile: high on high density lipoprotein (HDL); low on low density lipoprotein (LDL).
  • The greater amount of HDL cholesterol in proportion to total cholesterol value, the lower the risk for developing coronary artery disease.

B. Purpose total cholesterol, lipoproteins, and triglycerides are screening tests to determine risk of atherosclerosis and heart disease.

  •  High cholesterol—increased risk of heart disease.
  •  High-density lipoprotein—lower risk of heart disease.
  •  Low-density lipoprotein—higher risk of heart disease.
  • Hypercholesterolemia combined with low levels of high-density lipoprotein increases risk of arteriosclerosis.
  •  High triglycerides—higher risk of acute myocardial infarction.

C. Variations.

  •  Serum cholesterol increased in biliary obstruction (cirrhosis), hypothyroidism, pancreatic disease, uncontrolled diabetes, and pregnancy.
  •  Serum cholesterol decreased in liver disease, hyperthyroidism, malnutrition, anemias, malabsorption of cholesterol.
  •  Triglycerides increased in hepatitis, pancreatitis, cirrhosis due to alcoholism, renal failure, acute myocardial infarction.
  •  Triglycerides decreased in hyperparathyroidism, pulmonary disease, malnutrition.

Laboratory Tests: Arterial Blood Studies

Focus topic: Laboratory Tests

A. Arterial blood gases (ABGs).

  •  Assesses respiratory function.
    a. Oxygen (pO2).
    (1) Increased may indicate polycythemia.
    (2) Decreased may indicate chronic obstructive pulmonary disease (COPD), lung cancer, sickle cell anemia, anemias, cystic fibrosis.
    b. Carbon dioxide (pCO2).
    (1) Increased may indicate COPD, emphysema, bronchitis, asthma attack, pneumonia, cerebral trauma, neurologic disorder.
    (2) Decreased may indicate anxiety, hysteria, tetany, increased temperature, delirium tremens (DTs), hyperthyroidism, salicylate poisoning.
    c. pH—high is alkalotic, low is acidotic.
    d. Oxygen saturation and bicarbonate (HCO3).
    (1) Oxygen saturation should be viewed with hemoglobin value.
    (2) Bicarbonate—if low (< 23) or high (> 27), indicates malfunction of metabolic process.
  •  Determines state of acid–base balance.
  •  Reveals adequacy of the lungs to provide oxygen and to remove carbon dioxide.
  • Assesses degree to which kidneys can maintain a normal pH.

B. Normal arterial values.

  •  Oxygen saturation—93–98%.
  •  PaO2—95 mm Hg.
  •  Arterial pH—7.35–7.45 (7.4).
  •  pCO2—35–45 mm Hg (40).
  •  HCO3 content—22–26 mEq/L.
  •  Base excess— –3 to +3 (0).

C. Acid–base imbalances.

  •  Respiratory acidosis.
    a. pH— < 7.35.
    b. pCO2— < 45 mm Hg.
    c. pO2—90 mm Hg.
    d. HCO3—24 mEq/L.
  •  Respiratory alkalosis.
    a. pH— > 7.45.
    b. pCO2—35 mm Hg.
    c. pO2—95 mm Hg.
    d. HCO3— < 22 mEq/L.
  •  Metabolic acidosis.
    a. pH— < 7.35.
    b. HCO3— < 22 mEq/L.
    c. pCO2—38 mm Hg.
    d. pO2—95 mm Hg.
    e. Cl—120 mEq/L.
    f. K—5.5 mEq/L.
  •  Metabolic alkalosis.
    a. pH— > 7.45.
    b. HCO3— > 26 mEq/L.
    c. pCO2—38 mm Hg.
    d. pO2—95 mm Hg.
    e. K—3.0 mEq/L.
    f. Cl—88 mEq/L.

FURTHER READING/STUDY:

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