Diagnostic Methods--Cardiac Tests

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LLU-PAST 548

Accuracy

"Trueness," ability to dx. TP + TN / TP+FP+TN+FN

Precision

Replicability

Sensitivity

Ability to accurately identify affected, as percentage--OR-- Percentage of affected that will test positive.
TP / TP+FN

Specificity

Ability to accurately identify unaffected, as percentage--OR-- Percentage of unaffected that will test negative. TN / TN+FP

Positive Predictive Value

Percentage of Positive Tests that are affected.
TP / TP+FP

Negative Predictive Value

Percentage of Negative Tests that are unaffected.
TN / TN+FN

Positive Likelihood Ratio

The "odds" of being affected when test is positive.
Sensitivity / (1-Specificity)

Negative Likelihood Ratio

The "odds" pf being unaffected when test is negative.
(1-Sensitivity) / Specificity

FALTs & 3 classes

Factors Affecting Laboratory Tests Preanalytic, analytic, post-analytic

Two classes of Pre-analytic FALT

In vivo (gender, age, race, diet, diurnal variation)
In vitro: specimen handling, sampling error)

Cardiac biomarker sequence

Myoglobin --> CK/CKMB --> Troponin --> LDH

NSTEMI vs STEMI

Non-ST elevation MI; ST elevation MI

Two STEMI groups

NQMI (No Q-waves current), QwMI (Q-waves current, indicate active MI)

CK-MB (CPK-MB) fx, use & value

Creatine Kinase MB. Phosphorylates creatine to make phosphocreatine. Cardiac marker @ >4.0 ng/mL

CK-MB limitations

Elevated in MD, Skeletal muscle injury, malnutrition, post-marathon, rhabdomyolysis, prostate & breast cancer

CK-MB timeline

4-6 hr, 12 hr, 48 hr

cTn fx, use & values

Cardiac troponin. Regulates calcium binding in cardiomyocytes.Gold standard for ACS, establishes irreversible necrosis. cTnT: >0.1 ng/mL; cTnI: >0.04 ng/mL

cTn limitations

Elevated in CHF, Aortic Dissection;
Hypotension, Arrhythmias, Rhabdo, Myocarditis (CHAD HARM)

cTn timeline

4-8 hr, 24 hr, 5-7 days. AT 12 hr, 100% Sensitivity

Myoglobin fx, use and values

O2-carrying protein in skeletal & cardiac muscle. Earliest marker for AMI. Male: 28-72 ng/mL; Female: 25-58 ng/mL.

Myoglobin limitations

Elevated in muscle damage, post-exercise, alcohol abuse. Need draws q2-3 hr

Myoglobin timeline

2-3 hr, 8-12 hr, 24 hr

LDH fx, use and values

Lactate Dehydrogenase. Converts pyruvate to lactate, releasing NAD+. Late AMI marker.
RATIO of LDH1 : LDH2 > 1 suggests MI.

LDH limitations

Elevated in renal, liver and hemolytic dz. (Best use is in hemolysis)

LDH timeline

24 hrs, 2-3 days, 3-10 days

ASO fx, use & values

Antistreptolysin O. Antibodies to streptolysin-O (also streptokinase, hyaluronidase & DNAse-B) following Rheumatic Fever, Scarlet fever, glomerulonephritis .
Tests for GpA Strep Ix, which may suggest valve dz. Normal Adult: <100 IU/mL. Kids Normal kid: <260 IU/mL

ASO limitations

Elevated after any Strep-A; Endocarditis, glomerulonephritis, & in healthy Strep-A carriers

Blood culture uses & procedure

Tests for bacterial Ix of pericardium (pericarditis) or valves (endocarditis). Most common bacteria are pnemococcus or TB. Pain worse supine, better w\sitting, leaning forward. Take 3 cultures from 3 locations, 2 of 3 must be positive in 3-7 days.

Blood culture procedure

Order 3 separate cultures. 5-7 days
Pair w/ Echo for pericarditis or SBE

Brain Natriuretic Peptide fx & use

BNP is made by the ventricles to reduce pressure (CHF, LVH/RVH). It causes natriuresis and diuresis. Allows you to stage CHF (stages 3 & 4) by NYHA classes

CHF symptoms & Best Test

Dyspnea on exertion, Orthopnea, Fatigue, Edema, Paroxysmal nocturnal dyspnea (PUFFY SWOLLEN SNORER) BNP test

BNP values & limitations

Normal: <100, up to 300 w/ age, female
Abnormal: >300
CHF can exceed 1000
IF positive, ECHO

Lipid Panel Components & Requirements

Cholesterol
Triglycerides
HD Lipoproteins
LD Lipoproeins
VLD Lipoproteins
FASTING

Total Cholesterol fx, lab use, values

Used to make steroids, membranes, vitamin D, bile acids. Tests for CHD & risk of Atherosclerosis
Good: <200
Borderline: 200-239
High: >240

Triglycerides fx, lab use, values

Carried BY lipoproteins FROM gut TO adipocytes. Tests for risk of Atherosclerosis.
Good: <150
Borderline: 150-199
High: 200-499
Plain scary: >500

TG Tx

Over 300: change diet & exercise
AT >500, risk pancreatitis. Medicate

HDL fx, lab use, values

Lipoprotein that transports cholesterol FROM tissues TO liver. HIGH HDL --> LOW CHD risk (inverse risk)
Near-zero risk: >75
Good: >60
Acceptable female: >50
Acceptable male: >40
2X CHD risk: <25

TC & HDL ratio for CHD

The higher the TC:HDL, the greater the risk of atherosclerosis and CHD

LDL fx, test uses and values

lipoprotein that carries cholesterol TO tissues FROM the liver. LDL levels are directly proportional to atherosclerosis and CHD risk
DM and CHD: <70
At risk for CHD: <100
Good: 100-129
Borderline: 130-159
High: >160
Scary: >190

Friedwalds formula & its use

Use when TG >400 to calculate LDL:
LDL = (TC - HDL - VLDL)

The FIVE CHD RISK factors

Smoking, HTN, Low HDL, FamHx premature CHD in male <55 or female <65; Age: Male >45, Female >55

Apolipoprotein Assays

ApA1:ApB -->HDL lipoproteins : LDL lipoproteins
More sensitivity & specificity than HDL : LDL ratio

ApE Assay

3 isoforms, E2, E3, E4; 2 of E2=>CHD risk

Cardio-CRP use

Cardio-C Reactive Protein; Acute phase inflammation marker. Coronary artery endothelial inflammation raises c-CRP

Prevalence

Number of "affecteds" in a population at one time.

Bayes' Theorem

Measures "value" of a test.
(Sen) (Prev) (100)/ (Sen) (Prev) + (1-Spec) (1-Sen)

Screening criteria

Prevalence, Consequences, Treatment, Predictive values, Cost

How often are cardiac markers run?

3X in 12-16 hr

VLDL calculation

TG/5. e.g., if TG = 450, VLDL = 90

Homocysteine

$$ test to identify potential damage to vascular endothelium. CHF & Atherosclerosis marker

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