INTRODUCTION

Sputum is a highly specialized watery, colorless and odorless product of the respiratory tract.

Expectorated sputum is always abnormal and it consists of mucus and a variety of cellular and noncellular materials. It is the most frequently received specimen from the respiratory tract. Both its collection and examination are advantageous as samples are easily obtained, cost effective and its cellular content is representative of the entire respiratory tract.

Indications for Sputum Examination

•• Smear and culture identification of causative organisms in suspected infection (e.g. pneumonia, tuberculosis).

•• Cytological examination for malignant cells, viral inclusions, asbestosis.

SPUTUM COLLECTION


•• The patient is instructed to cough up to get the sputum proper and the same is collected in a wide mouthed sterile, glass/plastic container with screw cap.

•• Induction of sputum: In those patients who cannot produce sputum spontaneously by deep coughing, a specimen of sputum may be induced. This is done by inhalation of appropriate solvents which are aerosolized to stimulate sputum production (e.g. aerosol of 15% sodium chloride and 20% propylene glycol for 20 minutes).

•• Early morning sputum sample is preferred for routine examination and 24 hours sample for the demonstration of tubercle bacilli by concentration method.

EXAMINATION OF SPUTUM

Sputum examination consists of 

(1) physical examination, 

(2) microscopic examination, and

(3) culture study.

Physical Examination

•• Quantity:

–– In bronchiectasis, large amount of purulent sputum is coughed out.

–– Large amount of watery sputum with pink tinge suggests pulmonary edema.

•• Appearance/color: Different colors of sputum and its causes are shown in Table 55.1.

•• Odor or smell: Foul smelling sputum is observed in bronchiectasis and lung abscess and is due to anaerobic bacterial infections.

Microscopic Examination

Staining of Sputum:

Two to three smears are made on a clean dry glass slides and are stained with:

•• Leishman stain or Wright stain for differential count.

•• Other stains (depends on the clinical/pathological features).

•• Gram’s stain for microorganisms.

•• Ziehl-Neelsen stain for acid-fast tubercle bacilli

•• Special stains for fungi.

•• Papanicolaou stain for study of malignant cells.

Cells

Normal sputum consists of a few neutrophils, few lymphocytes, carbon-laden macrophages, occasional eosinophils and red cells. Various types of cells seen in sputum and their significance are shown in Table 55.2.

Other Structures

•• Curschmann spiral: 

They appear as spiral structures with a central thread found in the sputum of patients with bronchial asthma. Their exact nature is not known.

•• Charcot-Leyden crystals: These appear as fine needle shaped or hexagonal colorless crystals, which are formed when the sputum is allowed to stand for some time. In bronchial asthma, they form due to the disintegration of eosinophils.

Parasites

•• Larvae of Strongyloides stercoralis and roundworm: They may be found in sputum of patients with corresponding parasitic infestations.

•• Entamoeba histolytica: Cysts or the trophozoites may be found when an amoebic liver abscess ruptures into the lungs.

•• Echinococcus granulosae: Scolices and hooklets of the larval form may be seen with the rupture of the hydatid cyst of the lungs into the bronchus.

Culture Study

Sputum culture may demonstrate the causative infectious agent.

Points to note:

•• Sputum is a highly specialized product of the respiratory tract and expectorated sputum is always abnormal.

•• Sputum examination consists of physical, microscopic examination and culture.

•• Microscopically, sputum smears are stained by Leishman stain (cell type), Gram’s stain(for microorganisms), Ziehl-Neelsen stain (for acid-fast tubercle bacilli) and Papanicolaou stain(for study of malignant cells).