From the Guidelines
For a patient presenting with orthopnea, initial laboratory tests should include a complete blood count, comprehensive metabolic panel, B-type natriuretic peptide (BNP) or NT-proBNP, cardiac troponins, and thyroid function tests to evaluate potential cardiac or pulmonary causes. These tests are indicated because orthopnea commonly suggests heart failure but can also result from respiratory conditions, and laboratory testing helps differentiate between causes while guiding treatment decisions. The BNP test is particularly valuable as elevated levels strongly correlate with heart failure severity, which is the most common cause of orthopnea 1. Some key points to consider when ordering lab tests for orthopnea include:
- Measuring plasma natriuretic peptide level (BNP, NT-proBNP or MR-proANP) to help differentiate AHF from non-cardiac causes of acute dyspnoea 1
- Assessing cardiac troponins, BUN (or urea), creatinine, electrolytes (sodium, potassium), glucose, complete blood count, liver function tests and TSH at admission 1
- Considering echocardiography immediately in haemodynamically unstable AHF patients and within 48 hours when cardiac structure and function are either not known or may have changed since previous studies 1
- Using arterial blood gases to determine oxygenation status and acid-base balance, and D-dimer testing if pulmonary embolism is suspected 1
- Assessing lipid profile and hemoglobin A1c to evaluate cardiovascular risk factors It is essential to prioritize these tests based on the patient's clinical presentation and suspected underlying causes of orthopnea, as they will guide further management and treatment decisions 1.
From the Research
Lab Tests for Orthopnea
The following lab tests are indicated for a patient presenting with orthopnea:
- Electrocardiogram (ECG) to assess cardiac function 2
- Complete blood count (CBC) to evaluate for anemia, infection, or other conditions that may contribute to orthopnea 2, 3, 4
- Basic metabolic profile to assess for electrolyte imbalances or other metabolic disorders 2, 3
- Liver function tests to evaluate for liver disease or other conditions that may affect fluid balance 2, 5
- Troponin to assess for cardiac damage or myocardial infarction 2
- Brain natriuretic peptide (BNP) to evaluate for heart failure, although it may not significantly change treatment or outcomes 2, 3
- Chest radiograph to assess for pulmonary edema, cardiomegaly, or other conditions that may contribute to orthopnea, although findings may not be definitive 2, 3
- Point-of-care ultrasound to assess for B-lines, cardiac function, and inferior vena cava size, which can facilitate diagnosis 2
- Spirometry to evaluate for respiratory conditions such as chronic obstructive pulmonary disease (COPD) or asthma 3
- D-dimer testing to rule out pulmonary embolism 3
- Pulmonary function studies to identify emphysema or interstitial lung diseases 3
- Computed tomography (CT) of the chest to diagnose suspected pulmonary causes of orthopnea 3