Blood tests can reveal a surprisingly wide range of lung problems, from acute oxygen deprivation and blood clots to chronic inflammatory conditions and even early-stage cancer. No single blood draw replaces imaging or breathing tests for a definitive lung diagnosis, but specific markers in your blood offer doctors critical clues about what is happening inside your lungs and how urgently you need further workup. In many cases, a blood test is the fastest or least invasive first step toward catching a lung problem early.
Arterial Blood Gases and Acute Lung Function
The most direct way blood work measures lung performance is through an arterial blood gas (ABG) test. Unlike a standard blood draw from a vein, an ABG sample comes from an artery, usually at the wrist, and tells doctors how well your lungs are moving oxygen into your blood and carbon dioxide out. The test measures the partial pressures of oxygen and carbon dioxide directly, along with pH and bicarbonate, giving a real-time snapshot of both gas exchange and your body’s acid-base balance.1PubMed Central. Arterial blood gases made easy
ABGs are most commonly used in hospitals, particularly in emergency rooms and intensive care units, where rapid changes in breathing status need to be caught quickly. If you are in respiratory distress, a ventilator is being adjusted, or you have an unexplained acid-base disturbance, an ABG is likely one of the first tests ordered. A less invasive alternative, pulse oximetry, estimates oxygen saturation through a finger clip, but it cannot measure carbon dioxide levels or detect more subtle gas-exchange problems. When precision matters, the arterial blood draw is still the standard.
Screening for Blood Clots in the Lungs
A pulmonary embolism, a blood clot lodged in the lung’s arteries, is a life-threatening emergency. One of the most commonly used blood tests for this is the D-dimer, which measures a protein fragment released when blood clots break down. The test is extremely good at ruling out a clot when the result comes back negative. In a large meta-analysis, D-dimer had a pooled sensitivity of about 97%, meaning it catches nearly every case, and a negative predictive value in one large study reached roughly 97% as well.2PubMed Central. Systematic review and meta-analysis of test accuracy for the diagnosis of suspected pulmonary embolism In that same study, only 14 of 543 patients with a negative D-dimer actually had a pulmonary embolism.3Clinics. Assessing D-dimer test specificity for pulmonary embolism diagnosis in emergency departments
The catch is specificity. D-dimer goes up for all sorts of reasons: surgery, infection, pregnancy, cancer, even normal aging. In that same emergency department study, only about 1 in 8 patients with a positive D-dimer actually had a pulmonary embolism, giving a positive predictive value of just 12.5%.3Clinics. Assessing D-dimer test specificity for pulmonary embolism diagnosis in emergency departments So a positive result does not confirm a clot; it means you need imaging, typically a CT pulmonary angiogram. Doctors use D-dimer strategically, most often in patients whose clinical risk for a clot is low to intermediate. In that context, a normal D-dimer can spare you an unnecessary scan and radiation exposure.
Infection Markers and Pneumonia
When doctors suspect a lung infection like pneumonia, blood tests for inflammation help guide treatment decisions. The two most commonly measured markers are C-reactive protein (CRP) and procalcitonin (PCT). Both rise in response to infection, and both are especially useful for hinting at whether a respiratory infection is bacterial rather than viral, since bacterial pneumonia typically warrants antibiotics and viral infections do not.
The evidence on which marker performs better is mixed and depends on the population. In adults presenting to primary care with lower respiratory tract infections, one study found that both CRP and procalcitonin predicted radiographic pneumonia with similar sensitivity, around 70-73%, but both had disappointingly low positive predictive values, topping out at about 28%.4PubMed Central. Procalcitonin versus C-reactive protein for predicting pneumonia in adults with lower respiratory tract infection in primary care In children, results lean slightly toward procalcitonin. One pediatric study found procalcitonin had better diagnostic accuracy than CRP for bacterial pneumonia, with a sensitivity of about 83% at a cutoff of 1 ng/mL compared to 57% for CRP.5PubMed Central. Is procalcitonin better than C-reactive protein for early diagnosis of bacterial pneumonia in children? However, another pediatric study noted that values for bacterial and viral pneumonia overlap considerably, making these tests unreliable on their own for distinguishing the two.6The Pediatric Infectious Disease Journal. Serum procalcitonin, C-reactive protein and interleukin-6 for distinguishing bacterial and viral pneumonia in children
The practical takeaway is that these blood markers are most useful alongside clinical judgment, imaging, and cultures rather than as standalone tests. Very high procalcitonin or CRP values make bacterial pneumonia more probable, but moderate elevations do not nail the diagnosis on their own.
Blood Eosinophils for COPD and Asthma
If you have chronic obstructive pulmonary disease (COPD) or asthma, your doctor may order a complete blood count with a differential specifically to look at your eosinophil count. Eosinophils are a type of white blood cell involved in allergic and inflammatory responses, and their level in your blood has become an important guide for treatment decisions in airway diseases.
In COPD, blood eosinophil counts help predict which patients will benefit from inhaled corticosteroids, particularly when it comes to preventing flare-ups.7PubMed Central. Role of eosinophils in airway inflammation of chronic obstructive pulmonary disease Current global guidelines use blood eosinophils as a biomarker alongside clinical assessment when deciding whether to add inhaled corticosteroids to regular bronchodilator treatment.8Respiratory Science. New GOLD COPD Guideline 2019: How We Deal with It? (Inhaled Corticosteroid Use and Blood Eosinophil Count) Patients with persistently low eosinophil counts tend to get less benefit from inhaled steroids, so the blood test helps avoid unnecessary medication and its side effects.
In asthma, the connection is similar but extends further. Specific IgE blood tests (sometimes called RAST tests) can identify the allergens driving allergic asthma, which guides both avoidance strategies and treatment choices. These quantifiable results can predict the likelihood of exacerbations and help determine whether a patient is a good candidate for biologic therapies or allergen immunotherapy.9PubMed Central. A Pragmatic Primary Practice Approach to Using Specific IgE in Allergy Testing in Asthma Diagnosis, Management, and Referral A high eosinophil count combined with specific IgE results paints a clearer picture of what type of asthma you have and which treatments are most likely to help.
Alpha-1 Antitrypsin Deficiency
One of the clearest examples of a blood test directly diagnosing a lung condition involves alpha-1 antitrypsin deficiency (AATD), a genetic disorder that can cause COPD and bronchiectasis, sometimes at a younger age than typical. Despite being relatively common, AATD is heavily underdiagnosed because many doctors do not routinely test for it.10PubMed Central. Improving Screening for Alpha-1 Antitrypsin Deficiency with Direct Testing in the Pulmonary Function Testing Laboratory
The test itself is straightforward: a blood sample measures your level of alpha-1 antitrypsin protein, and if it is low, genetic testing confirms the specific mutations involved. Early diagnosis matters because it can change the course of treatment (including enzyme replacement therapy for eligible patients) and alerts family members to get tested. Current guidelines recommend that anyone diagnosed with COPD or unexplained bronchiectasis be screened at least once, but in practice this step often gets skipped.
Tumor Markers and Liquid Biopsy for Lung Cancer
Routine blood tests cannot reliably screen for lung cancer in people without symptoms. Standard tumor markers like CEA, CYFRA 21-1, and CA19-9 are sometimes elevated in lung cancer, but they also go up in benign conditions and are not sensitive enough for early detection on their own. One study found that combining six different tumor markers improved sensitivity for small cell lung carcinomas to about 80%, but even that panel missed a significant fraction of cases.11iLABMED. Clinical utility of six serum tumor markers for the diagnosis of lung cancer Individual markers like CEA were better for some subtypes (adenocarcinoma, for example) and weaker for others.12PubMed Central. The Indicative Value of Serum Tumor Markers for Metastasis and Stage of Non-Small Cell Lung Cancer In practice, traditional tumor markers are more useful for monitoring known cancers than for finding new ones.
The more exciting development is liquid biopsy, a blood test that detects fragments of tumor DNA, RNA, or other molecules shed by cancer cells into the bloodstream. Circulating tumor DNA (ctDNA) has emerged as one of the more reliable molecular tools for tracking lung cancer, with potential applications in early diagnosis, monitoring treatment response, and watching for recurrence.13PubMed. Circulating tumor DNA as liquid biopsy in lung cancer: Biological characteristics and clinical integration Newer assays that analyze cell-free DNA fragment patterns and end-motifs have shown the ability to detect early-stage lung cancers from very small blood samples.14Journal of Thoracic Oncology. Detection of Early-Stage Lung Cancer Using Cell-Free DNA Fragment and End-Motif Analysis
Liquid biopsy is not yet a routine screening tool for the general population. Most applications are still in clinical research or are used for patients already suspected of having cancer. But the technology is advancing quickly, and it represents one of the most promising pathways toward a blood-based lung cancer screening test.15PubMed Central. Liquid biopsy for early detection of lung cancer
Tracking Interstitial Lung Disease and Pulmonary Fibrosis
Interstitial lung diseases (ILDs), including idiopathic pulmonary fibrosis, are a group of conditions where scarring or inflammation damages the tissue between the air sacs. These diseases are typically diagnosed with imaging and sometimes lung biopsy, but a blood marker called KL-6 (Krebs von den Lungen-6) has gained attention as a way to track disease activity and progression without repeated scans.
KL-6 levels are significantly higher in patients with ILD than in healthy people. In one study, the marker had a sensitivity of about 77% and specificity of about 93% at an optimal cutoff, giving an overall accuracy around 89% for distinguishing ILD patients from controls.16International Journal of General Medicine. Diagnostic Value of Serum KL-6 in Interstitial Lung Diseases Levels also vary by ILD subtype: pulmonary alveolar proteinosis tends to produce very high KL-6 readings, while sarcoidosis produces much lower ones.16International Journal of General Medicine. Diagnostic Value of Serum KL-6 in Interstitial Lung Diseases
Where KL-6 really shines is in tracking disease over time. Baseline levels alone do not predict well who will get worse, but rising KL-6 levels over follow-up visits do. In one study, rising KL-6 was a significant predictor of disease progression on the next visit, and this held true specifically for idiopathic pulmonary fibrosis patients as well.17PubMed Central. Sequential changes of serum KL-6 predict the progression of interstitial lung disease KL-6 concentration, alone or combined with other clinical factors, allows effective risk stratification for disease progression at any point in the disease course.18PubMed Central. Serum KL-6 as a Biomarker of Progression at Any Time in Fibrotic Interstitial Lung Disease
Another lung-derived protein tracked in blood is surfactant protein D (SP-D). Surfactant proteins are normally found in the lung lining, so their presence in the bloodstream signals lung tissue injury. In a large COPD study, serum SP-D levels were significantly higher in people with airflow obstruction than in smokers without obstruction, and those with the highest SP-D levels had about a 30% increased risk of COPD exacerbations over the following year.19European Respiratory Journal. Serum surfactant protein D is steroid sensitive and associated with exacerbations of COPD Changes in SP-D also tracked well with changes in health status over a three-month period in patients with severe COPD, suggesting it could serve as a monitoring biomarker alongside standard lung function tests.20PubMed Central. Circulating surfactant protein D as a potential lung-specific biomarker of health outcomes in COPD: a pilot study
When Autoimmune Diseases Attack the Lungs
Lung damage sometimes turns out to be the first visible sign of an autoimmune condition like rheumatoid arthritis, scleroderma, or mixed connective tissue disease. In these cases, blood tests for autoantibodies can be the key to identifying the underlying cause. An extended panel of autoantibody testing can detect connective tissue disease-associated interstitial lung disease even before patients develop symptoms outside the lungs.21PubMed. Autoantibodies in interstitial lung diseases
The specific autoantibody pattern often points to the particular autoimmune disease. For example, one study found that anti-Scl-70 antibodies were enriched in scleroderma-related lung disease, anti-RNP/Sm in mixed connective tissue disease-related lung disease, and anti-SSA/Ro in rheumatoid arthritis-related lung disease.22PubMed Central. Spectrum of autoantibodies and other serological parameters in connective tissue disease–associated interstitial lung disease patients Antinuclear antibody (ANA) positivity was also higher in the connective tissue disease-ILD group compared to controls, particularly at high titers with a speckled pattern.22PubMed Central. Spectrum of autoantibodies and other serological parameters in connective tissue disease–associated interstitial lung disease patients
Despite their usefulness, there is no universally agreed-upon panel for which autoantibodies to test on the initial assessment, and opinions vary on when serial retesting makes sense.23PubMed Central. Role of Autoantibodies in the Diagnosis of Connective-Tissue Disease ILD (CTD-ILD) and Interstitial Pneumonia with Autoimmune Features (IPAF) In practice, if you have been diagnosed with interstitial lung disease and there is no obvious cause like an occupational exposure, a broad autoantibody panel is a reasonable next step. Catching the autoimmune connection early changes treatment dramatically, since immunosuppressive therapy rather than anti-fibrotic medication is typically the right approach.
Pulmonary Hypertension and Heart-Lung Overlap
Pulmonary arterial hypertension (PAH), a condition of dangerously high blood pressure in the lung’s arteries, is typically diagnosed by measuring pressures directly with a heart catheter. But a simpler blood test, BNP or its relative NT-proBNP, plays an important role in screening and monitoring. These peptides are released by heart muscle cells under mechanical strain, and because PAH puts enormous stress on the right side of the heart, blood levels of BNP rise in proportion to the severity of the disease.
Circulating BNP levels correlate with both mean pulmonary arterial pressure and pulmonary vascular resistance, and elevated levels are associated with higher mortality in PAH patients. Falling BNP levels after treatment correlate with improved survival, making it a practical way to gauge whether therapy is working without repeating invasive catheterizations.24PubMed Central. Brain natriuretic peptide in pulmonary arterial hypertension: biomarker and potential therapeutic agent BNP and NT-proBNP are now incorporated into several PAH risk stratification tools and are also used in screening algorithms for patients with systemic sclerosis, a connective tissue disease with a high risk of developing PAH.25European Respiratory Review. BNP/NT-proBNP in pulmonary arterial hypertension: time for point-of-care testing?
One important caveat: BNP and NT-proBNP are not specific to the lungs. Left-sided heart failure, kidney disease, and other conditions raise these levels too. An elevated BNP tells you the heart is under stress but does not by itself pinpoint the lungs as the source. Context from echocardiography and clinical history is needed to connect the dots.
Neonatal and Pediatric Lung Problems
Blood biomarker research has expanded into neonatal intensive care as well. Extremely premature infants face a high risk of bronchopulmonary dysplasia (BPD), a chronic lung disease that develops in the first weeks of life. Researchers have identified over 100 blood proteins that show distinct patterns in infants who go on to develop BPD, many related to immune function and lung development.26PubMed Central. Early-life serum protein profiles associated with bronchopulmonary dysplasia in extremely preterm infants While these are not yet standard clinical tests, they point toward a future where blood draws in the first days of life could help identify which premature infants are at highest risk and might benefit from earlier or more aggressive lung-protective strategies.
For neonatal respiratory distress syndrome specifically, researchers have explored inflammatory markers like interleukins and newer candidates like ANGPTL4 (a protein involved in metabolism and inflammation) for both diagnosis and prognosis, especially when combined with lung ultrasound findings.27PubMed Central. Research progress on biomarkers associated with neonatal respiratory distress syndrome Most of this work is still in early-stage, single-center studies, so these markers have not yet crossed into routine nursery practice.
Emerging Multi-Marker Panels
The future of lung-related blood testing is moving toward combinations of markers rather than single tests. One research group developed a panel combining three metabolites and one protein that diagnosed stable COPD with about 94% sensitivity and 95% specificity, a level of accuracy far beyond any single blood marker currently in use.28PubMed Central. Proteomics and metabolomics profiling reveal panels of circulating diagnostic biomarkers and molecular subtypes in stable COPD The same panel showed even stronger performance in distinguishing advanced COPD from milder disease. Approaches like this, drawing on proteomics (the study of all the proteins in your blood) and metabolomics (the study of small molecules), are still primarily research tools, but they suggest that a comprehensive blood-based lung health panel could become clinically available within the coming years.
This trajectory mirrors what happened with cardiovascular risk assessment, where individual markers like cholesterol were gradually supplemented with multi-marker risk scores. For lung disease, the challenge is greater because the lungs can be affected by so many different processes: infection, autoimmunity, fibrosis, cancer, vascular obstruction, genetic deficiency. No single panel is likely to cover all of these. But for specific conditions like COPD, where patients already get regular blood draws, adding a few targeted markers to the standard panel could meaningfully improve how early and how precisely the disease is managed.