What laboratory tests should be ordered for suspected heart failure?

Laboratory Tests for Suspected Heart Failure

For any patient with suspected heart failure, order a comprehensive initial laboratory panel including: complete blood count, serum electrolytes (sodium, potassium, calcium, magnesium), renal function tests (creatinine and estimated GFR), glucose, lipid profile, liver function tests, thyroid-stimulating hormone, urinalysis, and natriuretic peptides (BNP or NT-proBNP). 1, 2

Essential Initial Laboratory Tests

Core Metabolic and Hematologic Panel

• Complete blood count to identify anemia, which commonly exacerbates heart failure symptoms and affects prognosis 1, 2
• Serum electrolytes including sodium, potassium, calcium, and magnesium to detect imbalances that affect cardiac function or result from diuretic therapy 1, 2
• Renal function tests (serum creatinine and estimated GFR) are critical for management decisions, medication dosing, and prognosis 1, 2
• Liver function tests to evaluate hepatic congestion from right heart failure and establish baseline before initiating medications like amiodarone or warfarin 1, 2
• Fasting blood glucose to identify diabetes, which is both a risk factor and common comorbidity 1, 2
• Lipid profile for cardiovascular risk assessment 1, 2
• Thyroid-stimulating hormone because thyroid disorders can mimic or aggravate heart failure 1, 2
• Urinalysis to detect proteinuria or renal abnormalities contributing to fluid retention 1, 2

Natriuretic Peptide Testing (Critical for Diagnosis)

BNP or NT-proBNP measurement is essential for supporting or excluding the diagnosis of heart failure. 1, 2

Cut-off Values for Acute Presentations (Emergency Department):

• BNP < 100 pg/mL makes heart failure unlikely (negative predictive value 99%) 1
• NT-proBNP < 300 pg/mL makes heart failure unlikely in acute settings 1
• For patients ≥50 years: NT-proBNP < 450 pg/mL rules out acute heart failure 1
• For patients >50 years: NT-proBNP < 900 pg/mL rules out acute heart failure 1

Cut-off Values for Non-Acute/Ambulatory Presentations:

• BNP < 35 pg/mL makes chronic heart failure unlikely 1
• NT-proBNP < 125 pg/mL makes chronic heart failure unlikely 1

Important caveat: Natriuretic peptides have high sensitivity (86-96% for NT-proBNP) and excellent negative likelihood ratios (0.08-0.23), making them particularly valuable for ruling out heart failure rather than confirming it. 3

Additional Tests Based on Clinical Context

Iron Studies

• Serum iron, ferritin, and transferrin saturation should be measured, as iron deficiency is common in heart failure and impacts symptoms and outcomes 2

Cardiac Troponin

• Troponin T or I may be useful for determining prognosis in hospitalized patients with acute decompensated heart failure and identifying potential ischemic etiology 2, 4
• Detectable troponin levels occur in approximately 48% of acute heart failure patients without acute coronary syndrome and carry independent prognostic value 4

Specialized Testing When Clinically Indicated

• Hemochromatosis screening when iron overload is suspected 2
• HIV testing in patients with risk factors or unexplained cardiomyopathy 2
• Rheumatologic disease testing when clinical suspicion exists 2
• Amyloidosis testing in unexplained heart failure with preserved ejection fraction, particularly in older patients 2

Critical Pitfalls and Interpretation Caveats

Natriuretic Peptide Limitations

BNP and NT-proBNP can be falsely elevated in:

• Advanced age (particularly women >60 years) 1, 2
• Renal dysfunction 1, 2, 5
• Atrial fibrillation 2
• Pulmonary hypertension 2
• Acute pulmonary embolism 1, 2

BNP and NT-proBNP can be falsely low in:

• Obesity (levels should be interpreted cautiously in obese patients) 1, 2
• Flash pulmonary edema 2
• Heart failure with preserved ejection fraction (HFpEF) 2

Key Clinical Context

• A completely normal ECG makes heart failure, especially with systolic dysfunction, unlikely (<10% probability) 1
• Natriuretic peptides should never be used in isolation but rather as part of comprehensive clinical evaluation including history, physical examination, ECG, and echocardiography 1, 5
• In stable chronic heart failure patients, BNP levels may be relatively lower than diagnostic thresholds used in acute settings 1

Serial Monitoring Requirements

After diagnosis, monitor renal function and electrolytes regularly, especially:

• After initiation or dose adjustment of diuretics, ACE inhibitors, ARBs, or aldosterone antagonists 1, 2
• During episodes of acute illness 2
• In patients with severe heart failure requiring frequent medication adjustments 2
• Watch specifically for hypokalemia (from diuretics), hyperkalemia (from RAAS antagonists), hyponatremia (disease progression marker), and worsening renal function 1, 2