Diagnostic tests
Blood tests
Tests to identify myocardial infarction
After a myocardial infarction (MI), damaged cardiac tissue releases significant amounts of enzymes and proteins into the blood. Specific blood tests help confirm the diagnosis of MI, reveal the extent of cardiac damage, help monitor healing progress, and assess reperfusion after the use of fibrinolytics.
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Serum cardiac biomarkers
Myoglobin
Elevated
First marker of cardiac injury after acute MI
Found in skeletal muscle
Creatine kinase (CK) and CK-MB
Both return to normal quickly
CK-MB most reliable when reported as a percentage of total CK (relative index)
Found in cardiac muscle (CK-MB) and skeletal muscle (CK)
Troponin I
Isotype of troponin found only in myocardium
Elevated
Specific to myocardial damage
Troponin T
Isotype of troponin that’s less specific to myocardial damage (can indicate renal failure)
Elevated
Determined quickly at bedside
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Values
Myoglobin
Normal value: 0 to 0.09 mcg/ml
Rises within 30 minutes to 4 hours
Peaks within 6 to 10 hours
Returns to baseline by 24 hours
CK-MB
Normal value: 38 to 190 units/L for men; 10 to 150 units/L for women
Rises within 4 to 8 hours
Peaks in 12 to 24 hours
May remain elevated for up to 96 hours
Troponin I
Normal value: Less than
0.4 mcg/ml (may vary depending on the laboratory)
Rises within 4 to 6 hours
Peaks in 12 hours
Returns to baseline in 3 to 10 days
Tests to identify the risk of heart disease
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Homocysteine (tHcy)
Normal value: < 13 umol/L
Excess levels
Irritate blood vessels, leading to atherosclerosis
Raise low-density lipoprotein (LDL) levels
Make blood clot more easily
High-sensitivity C-reactive protein (hs-CRP)
Normal value: 0.1 to 0.3 mg/dl
Excess levels: May indicate increased risk of coronary artery disease (CAD)
Triglycerides
Normal value: < 150 mg/dl
Excess levels: Help with early identification of hyperlipidemia and identification of patients at risk for CAD
Total cholesterol
Normal value: < 200 mg/dl for adults; < 170 mg/dl for children and adolescents
Excess levels: May indicate hereditary lipid disorders, CAD
Evaluating lipid test results
Use this chart to determine an adult patient’s risk of CAD.
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Lipoprotein fractionation
Lipoprotein fractionation tests isolate and measure high-density lipoproteins (HDLs), LDLs, and very-low-density lipoproteins (VLDLs). Each of these particles is composed of protein, cholesterol, and triglyceride in varying amounts.
HDL
Primarily protein
Test measures the actual amount in the blood
The higher the level, the lower the risk of CAD
Normal values for males: 35 to
65 mg/dl; for females, 35 to 80 mg/dl
LDL
Mainly cholesterol
Equal to total cholesterol – HDL cholesterol – VLDL cholesterol (when triglyceride level is below 400 mg/dl)
The higher the LDL level, the higher the risk of CAD
Normal levels for individuals without CAD, < 130 mg/dl
Optimal levels for individuals with CAD, < 100 mg/dl
Tests to identify the risk of heart failure
Heart cells produce and store two neurohormones — A-type natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) — that help ensure cardiac equilibrium. Disruptions in fluid balance within the circulatory system trigger release of these hormones, which act as natural diuretics and antihypertensives.
BNP
Found in ventricular tissue
Helps accurately diagnose and grade heart failure severity
Normal value: < 100 pg/ml
Correlating the degree of heart failure with I3NP level
The higher a patient’s level of BNR the greater the degree of heart failure. In turn, the greater the degree of heart failure, the more the patient’s ability to perform activities of daily living (ADLs) will be impaired. Use this chart to help you plan your nursing care.
Tests for general screening
General screening tests are used to evaluate overall health and response to treatment.
Electrolyte tests
Electrolytes — which occur in the fluids both inside and outside cells — are crucial for nearly all cellular reactions and functions.
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Sodium, chloride, carbon dioxide
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▲ Potassium
Most critical value
Has narrow therapeutic range
Imbalances cause life-threatening arrhythmias
Affected by diuretics, penicillin G, some nonsteroidal anti-inflammatory drugs.
● Calcium
High values cause cardiac toxicity and arrhythmias
Elevations commonly caused by cancer or hyperparathyroidism
▪ Magnesium
High values cause ECG changes, ventricular tachycardia, and ventricular fibrillation
Low values cause ECG changes, bradycardia, and hypotension
Sodium
Maintains osmotic pressure, acid-base balance, and nerve impulse transmission
Levels decreased in severe heart failure
Decreased by diuretics, high triglycerides, and low blood protein
Chloride
Partners with sodium to maintain fluid and acid-base balance
Low levels in heart failure and metabolic acidosis
Carbon dioxide
Primarily made up of bicarbonate
Regulated by the kidneys
Levels lowered by thiazide diuretics
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Coagulation teste
Activated partial thromboplastin time (aPTT), prothrombin time (PT), bleeding time, and activated clotting time (ACT) are tests that measure clotting time. They’re used to measure response to treatment as well as to screen for clotting disorders.
Common tests for clotting
Test | Action | Clinical uses | Location performed | Normal range | Therapeutic ranges | Panic value |
ACT | Measures overall coagulation activity | ♥ Evaluates effects of high dose heparin therapy during cardiac procedures | Bedside | 70 to 120 seconds | 2 times normal range | Unknown |
Bleeding time | Determines platelet function abnormalities | ♥ Screens for platelet abnormalities before or during surgery ♥ Used to diagnose von Willebrand’s disease, vascular disorders, hemostatic dysfunctions | Bedside | 3 to 10 minutes | Unknown | > 15 minutes |
aPTT | Measures defects in intrinsic and common clotting pathways | ♥ Evaluates effects of heparin therapy ♥ Assesses overall coagulation system | Laboratory | 21 to 35 seconds | 2 to 2.5 times normal range | > 70 seconds |
PT | Directly measures deficits in extrinsic and common clotting pathways | ♥ Evaluates effects of coumar therapies ♥ Assesses for vitamin K deficiency ♥ Used to diagnose liver failure | Laboratory | 11 to 13 seconds | 2 to 2.5 times normal range | > 30 seconds |
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