Gram Stain

CPT: 87205
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Test Details

Use

Determine the presence of microörganisms and to evaluate the type of specimen by type of cells seen (eg, PMN, epithelial)

Limitations

Organism isolation and identification will usually be performed only if culture is requested. Request for Gram stain will not lead to stain for mycobacteria (TB). For detection of tubercle bacilli, an acid-fast stain must also be requested. Certain organisms do not stain or do not stain well with Gram stain (eg, Legionella pneumophila). As many as 30% of cases of bacterial meningitis have a negative Gram stain. Gram stain is not reliable for diagnosis of cervical, rectal, pharyngeal, or asymptomatic urethral gonococcal infection. In acute bacterial meningitis in adults, the most frequent error was misidentification of Listeria as Streptococcus pneumoniae in smears.1

Reference Interval

Depends on site of specimen

Additional Information

Gram stain is recommended (at an additional charge) with all anaerobic cultures, lower respiratory specimens, wound specimens, tissue specimens, and sterile body fluids. In addition, a Gram stain may be useful in demonstrating Neisseria gonorrhoeae or Mobiluncus with genital specimens. Gram stains are usually scanned for the presence or absence of white blood cells (indicative of infection) and squamous epithelial cells (indicative of mucosal contamination). A sputum specimen showing >25 squamous epithelial cells/lpf, regardless of the number of white blood cells, is indicative that the specimen is grossly contaminated with saliva and the culture results cannot be properly interpreted. Additional sputum specimens should be submitted to the laboratory if evidence of contamination by saliva is revealed.

The Gram stain can be a reliable indicator to guide initial antibiotic therapy in community-acquired pneumonia. It is imperative that a valid sputum specimen be obtained for Gram stain. In a well designed trial, valid expectorated sputum was obtained in 41% (59 of 144) of patients. The Gram stain is reliable but not infallible. Its principal limitations in the diagnosis of pulmonary infections are in detection of H influenzae and in differentiating polymicrobic pneumonia from background contamination of the specimen by oropharyngeal flora.2 Although mycobacteria have classically been considered to be gram-positive or faintly gram-positive, they are more correctly characterized as “gram-neutral” on routine stains.3 Culture for mycobacteria should be undertaken when purulent sputum without stainable organisms is encountered.

Gram stain is the most valuable diagnostic test in bacterial meningitis that is immediately available.4 Organisms are detectable in 60% to 80% of patients who have not been treated, and in 40% to 60% of those who have been given antibiotics.4 Its sensitivity relates to the number of organisms present. The sensitivity of the Gram stain is greater in gram-positive infections, and is only positive in 50% of the instances of gram-negative meningitis. It is positive even less frequently with listeriosis meningitis or with anaerobic infections.4 Culture and Gram stain should have priority over antigen detection methods if only a small volume of CSF is available.5

Specimen Requirements

Specimen

Material from infected area

Volume

Smear (air-dried) made at bedside or immediately after collection is preferred or one made in laboratory from swab or clinical material.

Container

Clean glass slides, swab in transport or clinical material in sterile container

Collection

Carefully select material from infected area with a sterile swab. Gently roll swab onto a clean glass slide to make a thin smear. Air dry the slide. Do not fix.

Storage Instructions

Maintain specimen at room temperature.

Causes for Rejection

Inappropriate specimen transport device; improper labeling; specimen received after prolonged delay (usually more than 72 hours); stool or fecal source (see White Blood Cells (WBC), Stool [008656]).

Clinical Information

Special Instructions

Indicate the source of specimen on the test request form. Label slide and slide holder.

Footnotes

1. Durand ML, Calderwood SB, Weber DJ, et al. Acute bacterial meningitis in adults. A review of 493 episodes. N Engl J Med. 1993 Jan7; 328(1):21-28. 8416268
2. Gleckman R, DeVita J, Hibert D, Pelletier C, Martin R. Sputum Gram stain assessment in community-acquired bacteremic pneumonia. J Clin Microbiol. 1988 May; 26(5):846-849. 2454937
3. Hinson JM, Bradsher RW, Bodner SJ. Gram-stain neutrality of Mycobacterium tuberculosis.Am Rev Respir Dis. 1981 Apr; 123(4 Pt 1):365-366. 6164319
4. Greenlee JE. Approach to diagnosis of meningitis. Cerebrospinal fluid evaluation. Infect Dis Clin North Am. 1990 Dec; 4(4):583-598. 2277190
5. Gray LD, Fedorko DP. Laboratory diagnosis of bacterial meningitis. Clin Microbiol Rev. 1992 Apr; 5(2):130-145. 1576585

References

Granoff DM, Murphy TV, Ingram DL, Cates KL. Use of rapidly generated results in patient management. Diagn Microbiol Infect Dis. 1986 Mar; 4(3 Suppl):157S-166S. 3486089
Provine H, Gardner P. The Gram's stained smear and Its interpretation. Hosp Pract. 1974; 9:85-91.
Riccardi NB, Felman YM. Laboratory diagnosis in the problem of suspected gonococcal infection. JAMA. 1979 Dec 14; 242(24):2703-2705. 387987
Smith AL. Bacterial meningitis. Pediatr Rev. 1993 Jan; 14(1):11-18. 8418448

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
008540 Gram Stain 664-3 018408 Gram Stain Result 664-3
Reflex Table for Gram Stain Result
Order Code Order Name Result Code Result Name UofM Result LOINC
Reflex 1 080031 Result 080032 Result 1 N/A
Reflex Table for Gram Stain Result
Order Code Order Name Result Code Result Name UofM Result LOINC
Reflex 1 080031 Result 080033 Result 2 N/A
Reflex Table for Gram Stain Result
Order Code Order Name Result Code Result Name UofM Result LOINC
Reflex 1 080031 Result 080034 Result 3 N/A
Reflex Table for Gram Stain Result
Order Code Order Name Result Code Result Name UofM Result LOINC
Reflex 1 080031 Result 080035 Result 4 N/A
Reflex Table for Gram Stain Result
Order Code Order Name Result Code Result Name UofM Result LOINC
Reflex 1 080031 Result 080036 Antimicrobial Susceptibility N/A

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