Diseases (15)


Gram stain is used to classify bacteria based on their forms, sizes, cellular morphologies and color stained by the Gram stain procedure. Gram stain is used for quick evaluation of the specimen and culture material before further testing is performed for infection detection and diagnosis.

Bacteria stain either gram-positive or gram-negative on the basis of differences in their cell wall compositions and architectures. Gram-positive species have a thick peptidoglycan layer and large amounts of teichoic acids; they are unaffected by alcohol decolorization and retain the initial stain, appearing deep violet if their cell walls are undamaged by age, antimicrobial agents, or other factors. Gram-negative species have a single peptidoglycan layer attached to an asymmetric lipopolysaccharide-phospholipid bilayer outer membrane interspersed with protein; the outer membrane is damaged by the alcohol decolorizer, allowing the crystal violet-iodine complex to leak out and be replaced by the counterstain.

Using Gram stain to detect the presence of bacteria and differentiate if an infection is caused by Gram-positive or Gram-negative bacteria often will give enough information to a health provider to initiate treatment with an appropriate antibiotic while waiting for more specific tests, such as a culture, to be completed. In addition, gram stain can detect other elements including white blood cells (WBC), yeast and epithelial cell. Detecting WBC is also important as they are frequently present with a bacterial, parasite or fungal infection.

A Gram stain may also be performed as part of the culture procedure. If bacteria are grown by culture, a Gram stain is performed to help determine the type of bacteria present and to help determine what other tests may need to be performed to definitively identify the cause of infection. Gram stain is the most valuable test for acute infections such as bacterial meningitis and blood cultures as it gives a quick result for initial antibiotic therapy until more testing is obtained.

Clinical Utility

  • As an aid in diagnosis of meningitis
  • As an aid in diagnosis of sepsis
  • As an aid in diagnosis of respiratory infection
  • As an aid in diagnosis of wound infection
  • As an aid in diagnosis of yeast infection
  • As an aid in diagnosis of variety of infections


Positive gram stain indicates infection with gram positive or gram negative bacteria. Results will differentiate gram positive and gram negative bacteria based on morphology, color and shape. It will describe presence of multiple bacteria, cells, white blood cells, yeast and other elements.

Reference Ranges

Usual Vaginal Flora present 
Nugent score: 0-3


Gram Stain and microscopy.

Specimen Collection

Biopsies, sputum, tracheal aspirates, bronchial wash, nasal swab, throat swab, body fluids, urine, variety of discharges, wounds


The best results are obtained from fresh specimens. Stability depends on the specimen type. Some swabs can have stability up to 48 hours.

Additional Testing

Bacterial culture from different sources, susceptibility testing on each isolate if detected by culture.

Turnaround Time

1-3 days.





A01.03Typhoid pneumonia
A02.22Salmonella pneumonia
A37Whooping cough
A40.3Sepsis due to Streptococcus pneumoniae
A48.1Legionnaires' disease
A48.2Nonpneumonic Legionnaires' disease [Pontiac fever]
A49.2Hemophilus influenzae infection, unspecified site
A54.84Gonococcal pneumonia
B96.3Hemophilus influenzae [H. influenzae] as the cause of diseases classified elsewhere
G00.0Hemophilus meningitis
G44.83Primary cough headache
J09Influenza due to certain identified influenza viruses
J09.X1Influenza due to identified novel influenza A virus with pneumonia
J12Viral pneumonia, not elsewhere classified
J12.0Adenoviral pneumonia
J12.1Respiratory syncytial virus pneumonia
J12.2Parainfluenza virus pneumonia
J12.3Human metapneumovirus pneumonia
J12.8Other viral pneumonia
J12.81Pneumonia due to SARS-associated coronavirus
J12.89Other viral pneumonia
J12.9Viral pneumonia, unspecified
J13Pneumonia due to Streptococcus pneumoniae
J14Pneumonia due to Hemophilus influenzae
J15Bacterial pneumonia, not elsewhere classified
J15.0Pneumonia due to Klebsiella pneumoniae
J15.1Pneumonia due to Pseudomonas
J15.2Pneumonia due to staphylococcus
J15.20Pneumonia due to staphylococcus, unspecified
J15.21Pneumonia due to staphylococcus aureus
J15.211Pneumonia due to Methicillin susceptible Staphylococcus aureus
J15.212Pneumonia due to Methicillin resistant Staphylococcus aureus
J15.29Pneumonia due to other staphylococcus
J15.3Pneumonia due to streptococcus, group B
J15.4Pneumonia due to other streptococci
J15.5Pneumonia due to Escherichia coli
J15.6Pneumonia due to other Gram-negative bacteria
J15.7Pneumonia due to Mycoplasma pneumoniae
J15.8Pneumonia due to other specified bacteria
J15.9Unspecified bacterial pneumonia
J16.0Chlamydial pneumonia
J16.8Pneumonia due to other specified infectious organisms
J17Pneumonia in diseases classified elsewhere
J18Pneumonia, unspecified organism
J18.0Bronchopneumonia, unspecified organism
J18.9Pneumonia, unspecified organism
J20.1Acute bronchitis due to Hemophilus influenzae
J20.9Acute bronchitis, unspecified
J22Unspecified acute lower respiratory infection
J40Bronchitis, not specified as acute or chronic
J41.0Simple chronic bronchitis
J44Other chronic obstructive pulmonary disease
J44.0Chronic obstructive pulmonary disease with (acute) lower respiratory infection
J44.1Chronic obstructive pulmonary disease with (acute) exacerbation
J44.9Chronic obstructive pulmonary disease, unspecified
J45.991Cough variant asthma
J80Acute respiratory distress syndrome
J84.111Idiopathic interstitial pneumonia, not otherwise specified
J85Abscess of lung and mediastinum
J85.1Abscess of lung with pneumonia
J85.2Abscess of lung without pneumonia
J95.1Acute pulmonary insufficiency following thoracic surgery
J95.2Acute pulmonary insufficiency following nonthoracic surgery
J95.3Chronic pulmonary insufficiency following surgery
J95.8Other intraoperative and postprocedural complications and disorders of respiratory system, not elsewhere classified
N11.1Chronic obstructive pyelonephritis
P23Congenital pneumonia
P23.0Congenital pneumonia due to viral agent
P23.1Congenital pneumonia due to Chlamydia
P23.2Congenital pneumonia due to staphylococcus
P23.3Congenital pneumonia due to streptococcus, group B
P23.4Congenital pneumonia due to Escherichia coli
P23.5Congenital pneumonia due to Pseudomonas
P23.6Congenital pneumonia due to other bacterial agents
P23.8Congenital pneumonia due to other organisms
Z87.01Personal history of pneumonia (recurrent)


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