Lab Values

Question 1

WBC

Answer 1

4,500-11,000

WBC counts are monitored in patients who are immunocompromised, including patients with heart transplants or in situations where there is concern for infection (e.g., after invasive procedures or surgery).

Question 2

Hgb

Answer 2

Male: 14-17.4 g/dl; Female: 12-16 g/dl

Question 3

Hct

Answer 3

Male: 42–52%; Female: 36–48%

The hematocrit represents the percentage of red blood cells found in 100 mL of whole blood. The red blood cells contain hemoglobin, which transports oxygen to the cells. Low hemoglobin and hematocrit levels have serious consequences for patients with cardiovascular disease, such as more frequent angina episodes or acute myocardial infarction.

Question 4

Platelets

Answer 4

140,000–400,000/mm
Platelets are the first line of protection against bleeding. Once activated by blood vessel wall injury or rupture of atherosclerotic plaque, platelets undergo chemical changes that form a thrombus. Several medications inhibit platelet function, including aspirin, clopidogrel, and intravenous glycoprotein IIb/IIIa inhibitors (abciximab, eptifibatide, and tirofiban). When these medications are given, it is essential to monitor for thrombocytopenia (low platelet counts).

Question 5

BUN

Answer 5

8–20 mg/dL

BUN and creatinine are end products of protein metabolism excreted by the kidneys.
Elevated BUN reflects reduced renal perfusion from decreased cardiac output or intravascular fluid volume deficit as a result of diuretic therapy or dehydration.

Question 6

Calcium

Answer 6

8.8–10.4 mg/dL

Calcium is necessary for blood coagulability, neuromuscular activity, and automaticity of the nodal cells (sinus and atrioventricular nodes).
Hypocalcemia: Decreased calcium levels slow nodal function and impair myocardial contractility. The latter effect increases the risk for heart failure.
Hypercalcemia: Increased calcium levels can occur with the administration of thiazide diuretics because these medications reduce renal excretion of calcium. Hypercalcemia potentiates digitalis toxicity, causes increased myocardial contractility, and increases the risk for varying degrees of heart block and sudden death from ventricular fibrillation.

Question 7

Creatinine

Answer 7

Male: 0.6–1.2 mg/dL
Female: 0.4–1.0 mg/dL

Both BUN and creatinine are used to assess renal function, although creatinine is a more sensitive measure. Renal impairment is detected by an increase in both BUN and creatinine. A normal creatinine level and an elevated BUN suggest an intravascular fluid volume deficit.

Question 8

Magnesium

Answer 8

1.8–2.6 mg/dL

Magnesium is necessary for the absorption of calcium, maintenance of potassium stores, and metabolism of adenosine triphosphate. It plays a major role in protein and carbohydrate synthesis and muscular contraction.
Hypomagnesemia: Decreased magnesium levels are due to enhanced renal excretion of magnesium from the use of diuretic or digitalis therapy. Low magnesium levels predispose patients to atrial or ventricular tachycardias.
Hypermagnesemia: Increased magnesium levels are commonly caused by the use of cathartics or antacids containing magnesium. Increased magnesium levels depress contractility and excitability of the myocardium, causing heart block and, if severe, asystole.

Question 9

Potassium

Answer 9

3.5–5 mEq/L

Potassium has a major role in cardiac electrophysiologic function.
Hypokalemia: Decreased potassium levels due to administration of potassium-excreting diuretics can cause many forms of arrhythmias, including life-threatening ventricular tachycardia or ventricular fibrillation, and predispose patients taking digitalis preparations to digitalis toxicity.
Hyperkalemia: Increased potassium levels can result from an increased intake of potassium (e.g., foods high in potassium or potassium supplements), decreased renal excretion of potassium, the use of potassium-sparing diuretics (e.g., spironolactone), or the use of angiotensin-converting enzyme inhibitors that inhibit aldosterone function. Serious consequences of hyperkalemia include heart block, asystole, and life-threatening ventricular arrhythmias.

Question 10

Sodium

Answer 10

135–145 mEq/L

Low or high serum sodium levels do not directly affect cardiac function.
Hyponatremia: Decreased sodium levels indicate fluid excess and can be caused by heart failure or administration of thiazide diuretics.
Hypernatremia: Increased sodium levels indicate fluid deficits and can result from decreased water intake or loss of water through excessive sweating or diarrhea.

Question 11

RBC

Answer 11

4.35 to 5.65 million red blood cells per microliter (mcL) of blood for men and 3.92 to 5.13 million red blood cells per mcL of blood for women

Question 12

ANC

Answer 12

2600-6000

Question 13

Chloride

Answer 13

97-107

Question 14

Phosphate

Answer 14

3-4.5

Question 15

Leukocytes

Answer 15

5,000-10,000