Skip to Main Content

Chapter 19. Evaluating Sputum and Pleural Effusions

A 70-year-old woman is seen in an acute care clinic for fever, chills, shortness of breath, and a cough. She states that her son's family stayed with her over Thanksgiving weekend and they had a respiratory infection from which they recovered. She later contracted the respiratory illness also, but after two weeks her symptoms have worsened. A sputum Gram stain is shown below. Which of the following is the most likely cause of this patient's current symptoms?


a. Haemophilus influenzae

b. Mycoplasma pneumoniae

c. Staphylococcus aureus

d. Respiratory syncytial virus

e. Streptococcus pneumoniae

The most correct answer is c, Staphylococcus aureus.

The Gram stain shows large gram-positive cocci, predominantly in clumps, some with a grape-like appearance that is typical of Staphylococcus. Haemophilus is a gram-negative coccobacillus; Mycoplasma pneumoniae cannot be cultured on routine media; RSV does not take up Gram stain; and Streptococcus pneumoniae are typically gram-positive, lancet-shaped diplococci.

A 55-year-old woman presents to the ER with new onset shortness of breath. Her chest x-ray shows a large right pleural effusion. A therapeutic thoracentesis is performed, and the fluid is sent to the laboratory. The pleural fluid/serum total protein ratio is 0.6 and the pleural fluid/serum LDH ratio is 0.7. Amylase and glucose levels are unremarkable on the pleural fluid. The culture and Gram stain are negative and the cytology results are negative for malignancy. Which of the following is most likely correct regarding the type and origin of her pleural fluid?

a. The fluid is a transudate, and congestive heart failure should be excluded.

b. The fluid is an exudate that is probably infected.

c. The fluid is an exudate, and pulmonary embolism should be excluded.

d. The fluid is a transudate, and nephrotic syndrome should be considered.

e. The fluid is an exudate that could be of pancreatic origin.

The most correct answer is c, an exudate and pulmonary embolism should be excluded.

The pleural fluid/serum total [protein] ratio and the fluid/serum [LDH] ratio both indicate the fluid is an exudate. The culture and Gram stain are both negative, so infection is less likely. Amylase levels are unremarkable, as is cytology, so malignancy or pancreatic origin is unlikely. Excluding a pulmonary embolism is the best next diagnostic step among the choices offered.

A 53-year-old ...

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.