NASAL SMEAR FOR EOSINOPHILS

Effective Date: 
Sun, 07/01/2012
Reviewed: 
Tue, 01/10/2017
Policy: 

Principal

Eosinophils from nasal smears can be easily distinguished from other
granulocytes when submitted to a cytochemical stain. A careful evaluation of
the cytological picture may be of diagnostic value in the differentiation of
allergy from super imposed infections, or in the attribution of a cause of
asthma in children and adults.

While it is well documented that the scope of eosinophil stains goes well beyond screening for allergic rhinitis when evaluating body fluids other than those of nasal origin, for compliance purposes with CLIA regulations, the scope of this procedure is restricted to the examination of nasal secretions. This procedure does not apply to the examination of specimens such as urine, stool, or GI secretions.

Materials and Equipment:  

  • Nasopharyngeal  swab
  • Glass microscope slides  (frosted)
  • Microscope
  • CAMCO STAIN:  Buffered Wrights Stain (Cambridge  Diagnostic Products, lnc.)
  • Coplin jars
  • Immersion oil

Specimen:  

A flexible wire Dacron, calcium alginate or cotton-tipped swab should  be passed gently through the nose into the nasopharynx and rotated to obtain sufficient test material.  The swab  is then gently rolled along the surface  of a  glass microscope slide.  The slide is labeled with the patient's full name and date and submitted to the  laboratory for examination.  This procedure  is performed  by the clinician.

Procedure: 
  1. In the laboratory, the specimen slide is first air dried.
  2. The air-dried slide is then stained with CAMCO STAIN:
  3. Dip slide  in  stain  for 10 seconds.
  4. Dip slide  in distilled water for 20 seconds  or more for darker staining.
  5. Observe slide under low dry lens for overall impression of specimen adequacy.
  6. Observe slide  under high dry lens for presence  of eosinophils.
  7. Confirm morphology using high oil lens.
  8. Refer to "Clinical Hematology Atlas" (see references) for guidance and illustrations of eosinophil morphology.
  9. Report the eosinophils as rare (0-3 whole slide), moderate(0-3 hpf) or many (>3 hpf).
  10. Report neutrophils using the same grading.

In non-allergic patients experiencing acute infections, few scattered
eosinophils may be noted mixed with neutrophils in the resolution stage
of the infection. If the number of eosinophils adds up to portray an
allergic response, it is recommended follow- up smears are done to
achieve distinction between the 2 cases. In the allergic patient, the
eosinophils will increment to large numbers whereas neutrophils will
disappear (provided a chronic infection does not complicate the picture).

Goblet cells, a constant and reliable feature observed in smears from
allergy patients even when eosinophils are not demonstrated. These cells
are normally not exfoliated; therefore, they will only be apparent if the
specimen was obtained by swabbing the mucosa. Goblet cells are
“edematous” columnar epithelial cells that are goblet in form. Their
cytoplasm is vacuolated and mostly without cilia. Cells eventually
rupture leaving the nucleus behind.

 

Key Points: 

Quality Control:  

Cell identification is performed quarterly with proficiency testing.

Limitations:  

lt is of utmost importance that the nasal smear be well prepared and stained according to procedure.  Precipitate formation may be due to inadequate or incorrect washing, dust,  or a dirty slide.  Excessive blue stain may be due to overstaining, excessive  alkalinity of the distilled water,  or inadequate washing.  Excessive red stain  may be due to  understaining or distilled water being too acidic.

Expected Values:

  • Neutrophils:  light purplish pink or lavender granules in cytoplasm
  • Eosinophils  bright red  or reddish orange granules in  cytoplasm
  • Basophils:  deep purple and violet black granules in cytoplasm

References:

  • Cameo Stain Pak Wrights Stain Product insert (Cambridge Diagnostic Products,  lnc.)
  • Hansel, F.K. The Cytology of the Secretions in Allergy. Clinical Allergy.
    Chapter 20, p. 408-418. The C.V. Mosby Co. St. Louis, Missouri, 1953.
  • Carr, J.H. and Rodak, B.F. Clinical Hematology Atlas, 3rd edition Saunders Elsevier 2009