Bronchoalveolar Lavage Differential Interpreter
Bronchoalveolar Lavage Differential Interpreter
A healthy non-smoker’s lavage is more than 85% macrophages. Lymphocytosis, neutrophilia and eosinophilia each open a different differential — but only if the lavage was good enough to interpret, which is the commonest reason these numbers mislead. This page checks the sample first and the cells second.
Bronchoalveolar lavage differential
Recovery + differential → patternRecovery 55%, epithelial cells 2%, lymphocytes 48%, neutrophils 6%, eosinophils 2%, CD4:CD8 6.5
Reference values and sample requirements
Abnormal above: lymphocytes 15%, neutrophils 3%, eosinophils 1%
Instil 100–300 mL in aliquots; recover ≥ 30%; epithelial cells ≤ 5%; count 400 cells
- recovery
- at least 30% of the instilled volume for an optimal alveolar sample. Abandon an aliquot returning under 5%. A poor return is characteristic of emphysema and airflow obstruction
- epithelial cells
- not more than 5%, or the specimen sampled airway rather than alveolus and the interpretation must be qualified. The most useful single quality marker on the report
- 400 cells
- the number that must be counted before a population representing less than 10% of the total can be estimated. A 100-cell differential cannot support a statement about eosinophils
- processing
- analyse within one hour in nutrient-poor medium, or transfer to tissue culture medium. Unsuitable beyond 24 hours. Viability above 90% is acceptable; below 80% suggests the sample is compromised
- smoking
- healthy smokers have up to a tenfold increase in macrophages per mL with no rise in lymphocytes, so their differential shows macrophages around 92% and lymphocytes around 5%. Interpret a smoker's lymphocyte percentage against that, not against the non-smoker range
- CD4:CD8 ratio
- the ATS guideline suggests subset analysis not be routine and cites “considerably increased (e.g. > 4)”. Raised in only 50–60% of sarcoidosis; sensitivity about 55% with specificity about 95% in the guideline's supplement, 0.70 and 0.83 in a meta-analysis of 1,885 subjects, which found cut-offs between 2 and 4 made no material difference
Worked example
Recovery 55%, epithelial cells 2%, lymphocytes 48%, neutrophils 6%, eosinophils 2%, CD4:CD8 6.5
Quality first: recovery 55% is above the 30% minimum, and 2% epithelial cells is within the 5% limit — the sample represents the alveolar space
Macrophages = 100 − 48 − 6 − 2 = 44%, well below the >85% of a healthy non-smoker
Lymphocytes 48% against an upper limit of 15% — a marked lymphocytosis
CD4:CD8 of 6.5 is considerably above the ATS guideline's example figure of 4
Together these support sarcoidosis in a compatible clinical and radiographic setting
They do not confirm it. The ratio is raised in only 50–60% of sarcoidosis, and pooled sensitivity is 0.70 with specificity 0.83 — so nodal or transbronchial biopsy is still the route to a diagnosis
Reference differential, and what smoking does to it
| Cell | Healthy non-smoker | Healthy smoker | Abnormal above |
|---|---|---|---|
| Alveolar macrophages | > 85% | Up to 92.5% | — (they are the balance) |
| Lymphocytes | 10–15% | About 5% | 15% |
| Neutrophils | < 3% | Modestly higher | 3% |
| Eosinophils | < 1% | Modestly higher | 1% |
| Squamous and bronchial epithelial cells | ≤ 5% | ≤ 5% | 5% — above this the sample is suboptimal |
Each pattern and what it opens
| Pattern | Threshold | Differential | Useful negative inference |
|---|---|---|---|
| Lymphocytosis | > 15% | Sarcoidosis (usually 20–40%), hypersensitivity pneumonitis (often > 50%), cellular NSIP, drug-induced pneumonitis, radiation pneumonitis, viral infection, lymphocytic interstitial pneumonia, chronic beryllium disease, lymphoproliferative disease | Above 30% argues against idiopathic pulmonary fibrosis. Below 30% makes hypersensitivity pneumonitis uncertain |
| Neutrophilia | > 3% | Infection first, then aspiration, acute respiratory distress syndrome, connective tissue disease, bronchiectasis, idiopathic pulmonary fibrosis (5–30% in up to 90%), acute interstitial pneumonia | A prominent neutrophilia unexplained by infection is consistent with acute interstitial pneumonia |
| Eosinophilia | > 1% | Drug-induced lung disease, asthma, allergic bronchopulmonary aspergillosis, parasitic infection, EGPA, cryptogenic organising pneumonia (2–25%), idiopathic pulmonary fibrosis (> 5% in up to 60%) | — |
| Marked eosinophilia | ≥ 25% | Acute or chronic eosinophilic pneumonia — the guideline states the diagnosis can be made on this finding | One of the few lavage findings that is diagnostic rather than suggestive |
| Macrophage-predominant | All within limits | Normal for a non-smoker; expected in a smoker | Does not exclude interstitial lung disease — counts are normal in 10–15% of sarcoidosis |
The CD4:CD8 ratio in sarcoidosis — what is actually established
| Source | Cut-off | Sensitivity | Specificity | Note |
|---|---|---|---|---|
| ATS guideline, Meyer 2012 | “Considerably increased (e.g. > 4)” | — | — | The guideline suggests lymphocyte subset analysis not be routine. It offers 4 as an example, not as a validated threshold |
| ATS guideline online supplement | Not stated | About 55% | About 95% | Also records that the ratio is raised in only 50–60% of sarcoidosis |
| Shen 2016 meta-analysis, 1,885 subjects | Studies used 2 to 4 | 0.70 (0.64–0.75) | 0.83 (0.78–0.86) | AUC 0.84, DOR 11.17. Meta-regression found the cut-off did not materially affect accuracy (p = 0.57) |
| The widely quoted “> 3.5” | 3.5 | — | — | No primary source found. It appears in review articles and laboratory handbooks without a derivation. It is not the ATS figure and it is not a cut-off any meta-analysis singles out |
Check the lavage before you read the cells
A bronchoalveolar lavage samples about a million alveoli, and the differential count on what comes back is genuinely informative about interstitial lung disease — provided that what came back came from the alveoli. That proviso is where most misinterpretation starts, which is why this page asks about the sample before it asks about the cells. The ATS guideline sets three quality requirements and all three are checkable off the report. At least 30% of the instilled volume should be recovered, from a total instillation of between 100 and 300 mL given in aliquots, with any aliquot returning under 5% abandoned. Not more than 5% of the cells should be squamous or bronchial epithelial cells, and above that the guideline says the specimen is suboptimal and the interpretation must be qualified as possibly not representing the alveolar space. And at least 400 cells must be counted before any population making up less than a tenth of the total — which includes eosinophils on almost every sample — can be estimated at all. A differential read off 100 cells cannot support a statement about eosinophils, and a poor recovery is itself a finding, being characteristic of emphysema and airflow obstruction.
Given a decent sample, a healthy non-smoker's lavage is more than 85% alveolar macrophages, with 10 to 15% lymphocytes, under 3% neutrophils and under 1% eosinophils. Each of those three minority populations opens a different differential when it rises. A lymphocytosis above 15% brings in sarcoidosis, hypersensitivity pneumonitis, cellular non-specific interstitial pneumonia, drug-induced and radiation pneumonitis, viral infection and lymphoproliferative disease, and it carries two useful negative inferences: above 30% it argues against idiopathic pulmonary fibrosis, and below 30% it makes hypersensitivity pneumonitis — which often exceeds 50% — unlikely. Neutrophilia above 3% means infection until proved otherwise, then aspiration, acute respiratory distress syndrome, connective tissue disease and idiopathic pulmonary fibrosis, in which 5 to 30% occurs in up to 90% of patients. Eosinophilia above 1% is non-specific and points first at drugs; at 25% or more the guideline says eosinophilic pneumonia can be diagnosed on the lavage alone, which makes it one of very few findings here that is diagnostic rather than suggestive.
Smoking has to be part of the reading. A healthy smoker has up to ten times as many macrophages per millilitre of lavage fluid with no absolute increase in lymphocytes, so the macrophage percentage rises towards 92% and the lymphocyte percentage falls to around 5%. A smoker reported at 14% lymphocytes is inside the non-smoker reference range and has a real lymphocytosis; a non-smoker's 14% is normal. The reference range on the report is almost always the non-smoker one, and nothing on the form tells the reader to adjust it.
The CD4:CD8 ratio deserves a paragraph of its own because the figure in common circulation does not survive checking. A ratio above 3.5 is widely quoted as supporting sarcoidosis, and no primary source for that number could be found — it appears in reviews and handbooks without a derivation. What is attributable is less flattering. The ATS guideline suggests lymphocyte subset analysis should not be a routine part of a lavage, and where it names a figure at all it writes “considerably increased (e.g. > 4)”; its own supplement records that the ratio is raised in only 50 to 60% of sarcoidosis, with sensitivity around 55% against specificity around 95%. A meta-analysis of 16 publications and 1,885 subjects pools sensitivity at 0.70 and specificity at 0.83, and found by meta-regression that cut-offs anywhere between 2 and 4 made no material difference to accuracy. So: measure it when sarcoidosis is a serious possibility and the lavage is already lymphocytic, read a high value as support for a picture you already believe, and never read a normal value as exclusion. The diagnosis is made on tissue. And the same restraint applies to the differential as a whole — the ATS guideline is clear that it is an adjunct to the high-resolution CT pattern, that it has no prognostic value, and that it should not be used to decide treatment.
Frequently asked questions
What is a normal bronchoalveolar lavage differential?
In a healthy non-smoker, more than 85% alveolar macrophages, 10 to 15% lymphocytes, under 3% neutrophils and under 1% eosinophils. Values above 15%, 3% and 1% respectively are abnormal. In a healthy smoker the macrophage percentage rises towards 92% and lymphocytes fall to about 5%, so the smoker's differential must be read against a different baseline.
How much lavage fluid needs to come back for the result to be valid?
At least 30% of the instilled volume, from an instillation of 100 to 300 mL given in aliquots, with any aliquot returning less than 5% abandoned. The sample should also contain no more than 5% squamous or bronchial epithelial cells, and at least 400 cells should be counted. A poor recovery is itself characteristic of emphysema and airflow obstruction.
What CD4:CD8 ratio indicates sarcoidosis?
No single cut-off is validated. The ATS guideline suggests subset analysis not be routine and offers “considerably increased (e.g. > 4)” as an example rather than a threshold; a meta-analysis of 1,885 subjects found cut-offs between 2 and 4 performed about equally. The commonly quoted 3.5 has no primary source we could trace. A high ratio supports sarcoidosis in a compatible picture; a normal one does not exclude it.
How sensitive is the CD4:CD8 ratio for sarcoidosis?
Poorly, on every published estimate. The ATS guideline's supplement gives sensitivity around 55% with specificity around 95%, and records that the ratio is raised in only 50 to 60% of patients with sarcoidosis. A meta-analysis pools sensitivity at 0.70 and specificity at 0.83. Tissue sampling remains how sarcoidosis is confirmed.
What does lavage eosinophilia mean?
Above 1% is abnormal and non-specific — drugs, asthma, allergic bronchopulmonary aspergillosis, parasitic infection, eosinophilic granulomatosis with polyangiitis, cryptogenic organising pneumonia and idiopathic pulmonary fibrosis all produce it. At 25% or more, the ATS guideline states that a diagnosis of pulmonary eosinophilia can be made on the lavage. Review every drug before anything else.
Can a normal lavage differential exclude interstitial lung disease?
No. Lavage cell counts are normal in 10 to 15% of patients with sarcoidosis, and the ATS guideline positions the differential as an adjunct to the high-resolution CT pattern rather than a standalone test. It also has no prognostic value and should not be used to decide on treatment.
Related calculators
References
- Meyer KC, Raghu G, Baughman RP, et al. An official American Thoracic Society clinical practice guideline: the clinical utility of bronchoalveolar lavage cellular analysis in interstitial lung disease. Am J Respir Crit Care Med. 2012;185(9):1004–1014.
- Shen Y, Pang C, Wu Y, et al. Diagnostic performance of bronchoalveolar lavage fluid CD4/CD8 ratio for sarcoidosis: a meta-analysis. EBioMedicine. 2016;8:302–308.
- Costabel U, Guzman J. Bronchoalveolar lavage in interstitial lung disease. Curr Opin Pulm Med. 2001;7(5):255–261.
- Wells AU. The clinical utility of bronchoalveolar lavage in diffuse parenchymal lung disease. Eur Respir Rev. 2010;19(117):237–241.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.