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Flashcards in Twenty Eight Deck (16):

How is sputum collected? What is then done and why?

Expectorated sputum is the most common lower respiratory
tract specimen received in the clinical microbiology laboratory.
Sputum can be collected either by spontaneous expectoration
or after sputum induction, which is collected following
instillation or inhalation of an irritating aerosol such as
hypertonic saline. Sputum induction is performed when the
patient cannot produce sputum. Generally, the fi rst morning
sputum samples are the best specimens; a volume of 5-10 mL
is usually adequate. Because many received specimens consist
mostly of pharyngeal secretions and upper airway cells
rather than sputum, the fi rst step in evaluating a specimen’s
suitability uses a Gram stain (Fig. 19.1). Use of such a Gram
stain assesses specimen acceptability for further processing,
and aids interpretation by identifying the morphology of any
likely etiologic agents of pneumonia in a specimen that is
acceptably purulent.


What determines whether a sputum sample is acceptable?

Ideally, a sputum sample examined microscopically
should contain 25 leukocytes/LPF. Sputum
specimens containing >25 squamous epithelial cells are
rejected because these represent oropharyngeal secretions
that will be heavily contaminated with normal throat fl ora.
Likewise, a sputum specimen containing no epithelial cells,
leukocytes, or bacteria is rejected because the specimen is
an inadequate representation of conditions in the intermediate
airways. Most hospital laboratories have well-established guidelines of this type, including stipulations as to the handling
of such potentially dangerous biological specimens.
These guidelines can be adjusted when a particular patient’s
needs are communicated to the laboratory personnel.


What does the gram stain report tell you?

The Gram stain report on a sputum sample includes the
types of organism seen, whether they are gram-positive or
-negative, and the architecture of the organism, whether cocci
or bacilli. Such information gives important clues as to possible
identifi cations of organisms found. For example, grampositive
cocci that appear as grape-like clusters raise suspicion
for Staphylococcus spp., while gram-positive lancet-shaped
diplococci suggest Streptococcus pneumoniae. The presence
of gram-negative coccobacilli often indicates Haemophilus
infl uenzae. In the same sputum report, the number of organisms
present is usually estimated as many, moderate, few, or
rare. In most laboratories, these terms pertain to the number
of similar organisms present per high power fi eld (HPF) using
oil immersion: many >10 organisms/HPF; moderate = 5-10
organisms/HPF, few = 1-5 organisms/HPF, and rare <1 organism/


What are some gross characteristics of sputum and what do they signify?

• Mucopurulent: Cystic Fibrosis, Pseudomonal Pneumonia

• Rusty: Pneumococcal Pneumonia

• Currant Jelly: Klebsiella Pneumonia

• Pink/Frothy: Pulmonary Edema

• Hemoptysis: Bronchitis, Bronchiectasis, Tumors,

PE, TB, Trauma, Pulmonary-Renal Syndromes

• Pseudohemoptysis: Serratia Pneumonia


What are some special stains that can be used for sputum? When is each used?

– Silver stains: Fungi including PJP

– Acid fast stains: Tb, Non-tuberculous

mycobacteria, Norcardia

– Direct florescent antibody: Legionella

– Wright’s stain: Asthma

– Cytologic preparation: Lung cancer


What are 4 possible gross appearances of pleural fluid and what might they mean clinically?

• Clear, straw colored: CHF, hepatic hydrothorax, hypoalbuminemia

• Bloody: trauma, malignancy, pulmonary infarction

• Purulent: infection (empyema)

• Milky white: Thoracic duct injury (Tryglycerides, “chylous”)

Rheumatoid pleural effusion:
whitish/yellowish green
(cholesterol, “pseudochylous”)


Describe Light's criteria to determine if something is an exudate.

• Light’s Criteria (traditional, 1972)

– Protpl/Prots > 0.5

– LDHpl/LDHs > 0.6

– LDHpl > 2/3rds of upper limit of normal of LDHs

If any one true then the fluid is characterized as an

(Clinical judgment required when values are near
the cut points.)


What are some common lab tests done on pleural fluid and what might they tell you?

• pH (low: bacteria, leukocytes, tumor cells)

• Glucose (low: infection, rheumatoid effusion)

• Amylase (elevated: esophageal perforation)

• Triglycerides (elevated: chylous effusions)

• Cholesterol (elevated: pseudochylous effusion)

• Albumin (low: hepatic hydrothorax)


What might the pleural fluid cell count tell you? What might the pleural fluid leukocyte differential tell you?

• Cell Count:

– Numerous RBCs: malignancy, trauma
– Numerous WBC (> 10,000): acute infection

• Differential:
– Neutrophils: Acute bacterial infections
– Lymphocytes: Tb, Lymphoma
– Eosinophils: PTX, PE with infarction


What can PF cytology tell you?

• Cytology: Cannot exclude a malignancy with a

single specimen (65% sensitivity) and need to



What kind of smears and cultures can be performed on PF and what do they tell you?

• Gram stain and bacterial cultures

– Anaerobic/aerobic mixed infections are relatively common

– Staph aureus and Strep pneumoniae

• AFB smear and culture

– Culture only positive in 1/3 of cases of Tb pleural effusions

– Tuberculous empyema is rare

• Fungal smear and culture


How is empyema defined and what is the treatment?

• Empyema: Abscess in the pleural space as defined by

aspiration of frank pus and/or organisms seen on the

gram stain of the fluid

• Requires drainage (Tube thoracostomy at a minimum)


What is BAL and what can it be used to diagnose?

• One type of specimen obtained during

diagnostic flexible bronchoscopy

• Properly performed a BAL can sample millions

of alveoli in a “liquid lung biopsy”.

• Can be diagnostic:

– Infectious pneumonias

– Eosinophilic pneumonia

– Diffuse alveolar hemorrhage

– Lung cancers


What are some possible gross charact. of BALF and what are they diagnostic of?

• Gross characteristics:

– Bloody (diffuse alveolar hemorrhage)

– Milky (pulmonary alveolar proteinosis)


What kinds of diagnoses can various cell count abnormalities point to ?

• Normal non-smokers:
– 130 cells/mm3
• 85 % macrophages

• High percentage of:

– Neutrophils: infectious pneumonia, ARDS

– Lymphocytes: sarcoidosis, hypersensitivity pneumonitis, pulmonary lymphoma

– Eosinophils: drug induced pneumonitis,
eosinophilic pneumonia, helminth infections


What is BALF cytology primarily used to diagnose? How can it diagnose ILDs?

• Cytology used

primarily to detect


• Flow cytometry used

in the diagnosis of ILDs

– CD4/CD8 ratio of T-

– If low: hypersensitivity


– If high: sarcoidosis