Papanicolaou EA36 Cervical Cytology Staining Protocol

1 Method Positioning

1.1 Purpose and Scope of Application

This protocol is used to establish the workflow for fixation, hydration, nuclear staining, cytoplasmic differential staining, dehydration, clearing, and mounting using the Papanicolaou EA36 system in cervical cytology specimens. Applicable samples include conventional cervical exfoliative cell smears and laboratory-validated liquid-based cytology preparations. The method is mainly used for cervical cytology screening, morphological observation related to cervical epithelial lesions, and routine cytological staining experiments.

1.2 Key Operational Points

(1) The main specimen types are cervical smears and cervical liquid-based cytology preparations. Staining parameters should be adjusted based on differential staining of cervical epithelial cells, nuclear structural clarity, and background cleanliness.

(2) EA36 is used in the cytoplasmic counterstaining step, with emphasis on controlling the differential staining layers among superficial cells, intermediate cells, columnar epithelial cells, and inflammatory background.

(3) Fixation, hydration, differentiation, bluing, OG6 primary staining, EA36 counterstaining, and final dehydration should be performed at fixed time points to facilitate within-batch consistency management.

1.3 Staining Quality Targets

(1) Cell nuclei should appear blue to dark blue, with clearly visible nuclear membranes, nucleoli, and chromatin granules.

(2) The cytoplasm of keratinized cells should appear orange-yellow, while non-keratinized squamous epithelial cells and columnar epithelial cells should show differential tones such as pink, blue-green, or green.

(3) The background should be clean. Mucus, inflammatory cells, and red blood cells should not significantly obscure epithelial cell structures. Slide transparency should support contour observation in areas with overlapping cells.

2 Sample, Fixation, and Staining Reagent Preparation

2.1 Sample Requirements

(1) Conventional cervical smears should be evenly spread or smeared immediately after sampling. The cell layer should not be too thick, and the slide surface should not show extensive mucus coverage or obvious blood clots.

(2) Liquid-based cytology preparations should be confirmed to have good cell adhesion and should not be exposed to air for prolonged periods before staining. If pretreatment results in insufficient cell adhesion, subsequent ethanol gradients and running-water rinsing may increase the risk of cell detachment.

(3) Damaged slides, label-contaminated slides, and obviously dried slides should be excluded before staining. Preparations that have undergone artificial degeneration caused by air drying should not be used as the basis for staining parameter optimization.

2.2 Fixation System

(1) Conventional smears are recommended to be fixed in 95% ethanol-glacial acetic acid fixative for 10–15 min. The fixative should completely cover the cellular area, avoiding residual air at the slide edges.

(2) If staining cannot be performed immediately after fixation, the slides should remain immersed in an appropriate concentration of ethanol and should not be removed and exposed to drying.

(3) During use, attention should be paid to decreased ethanol concentration, staining residue, and water carryover. The fixative should be replaced in time if it becomes turbid, develops an abnormal odor, or has been reused for an excessively long period.

2.3 Staining Reagent and Working Solution Inspection

(1) Before use, hematoxylin staining solution should be checked for metallic sheen, precipitates, or crystals. Filtration may be performed when necessary.

(2) Differentiation solution and bluing solution should be replaced daily or according to usage volume. Decreased differentiation efficiency may cause overly dark nuclear staining, while insufficient bluing may affect nuclear color stability and subsequent cytoplasmic differential staining.

(3) Orange G6 and EA36 staining solutions should remain clear, and bottle openings should not be left open for prolonged periods. If obvious precipitation, overall color shift, or unstable differential staining between batches occurs, quality control slides should be used for confirmation before processing formal samples.

(4) Ethanol gradients and xylene should be kept clean. If water is carried into absolute ethanol or xylene, slides are prone to fogging, grayish background, or decreased transparency after mounting.

3 Standard Operating Procedure

3.1 Fixation and Hydration

(1) Immediately after preparation, place the cell smear into 95% ethanol-glacial acetic acid fixative and fix for 10–15 min.

(2) Remove the slide and place it sequentially in 95% ethanol, 80% ethanol, and 70% ethanol for 1 min each.

(3) Transfer the slide into distilled water or tap water for soaking or rinsing for 1 min, allowing the preparation to reach the hydrated state suitable for hematoxylin nuclear staining.

3.2 Nuclear Staining, Differentiation, and Bluing

(1) Place the hydrated slide into a validated hematoxylin staining solution and stain for 5–10 min. The staining time should be slightly adjusted according to the age of the staining solution, temperature, and nuclear staining intensity of the quality control slide.

(2) After hematoxylin staining, rinse with tap water for 2 min to remove surface excess stain.

(3) Differentiate with 1% acid alcohol for approximately 4–5 s, or with 0.5% hydrochloric acid aqueous solution for approximately 10 s. Rinse immediately for 2 min after differentiation to avoid continued decolorization.

(4) Transfer the slide into bluing solution for 2 min, then rinse with tap water for 2 min. After bluing, the nuclei should change from reddish-purple to stable blue.

3.3 Dehydration Before Cytoplasmic Staining

(1) Place the slide sequentially in 70% ethanol and 80% ethanol for 2 min each.

(2) Then place the slide in 95% ethanol (I) and 95% ethanol (II) for 2 min each. This step adjusts the slide to an ethanol environment suitable for OG6 and EA36 cytoplasmic staining.

3.4 Orange G6 Primary Staining

(1) Place the slide in Orange G6 staining solution and stain for 2 min.

(2) After staining, place the slide sequentially in 95% ethanol (I) and 95% ethanol (II) for 2 min each to remove excess Orange G6 and avoid overly strong keratinized cytoplasmic staining or residual orange-yellow background.

3.5 EA36 Counterstaining

(1) Place the slide in EA36 staining solution and stain for 3–5 min. When the cervical cell load is high or the background is thick, quality control slides should be used first to determine whether the upper time limit is needed.

(2) After EA36 staining, place the slide in 95% ethanol (I) and 95% ethanol (II) for 1 min each. This step removes excess floating stain and directly affects the balance among pink, blue-green, and green tones; it should not be extended arbitrarily.

3.6 Final Dehydration, Clearing, and Mounting

(1) Place the slide in absolute ethanol (I) and absolute ethanol (II) for 1 min each to complete final dehydration.

(2) Transfer the slide into xylene (I) and xylene (II) for clearing, approximately 2 min each. Xylene should be replaced if it becomes turbid, contains water, or becomes colored.

(3) Add neutral mounting medium and cover with a coverslip, avoiding bubbles, insufficient mounting medium, or overflow. After mounting, allow the mounting medium to stabilize before microscopic observation or archiving.

Table 1 Key steps and control points in Papanicolaou EA36 cervical cytology staining

Step	Reagent/Treatment	Recommended Time	Purpose	Control Point
Fixation	95% ethanol-glacial acetic acid fixative	10–15 min	Maintains nuclear and cytoplasmic morphology	Slides must be wet-fixed; avoid slide drying
Hydration	95% ethanol → 80% ethanol → 70% ethanol → water	1 min each	Brings the slide into the hydrated state required for nuclear staining	The gradient should be stable; avoid sudden hydration that may cause cell detachment
Nuclear staining	Hematoxylin staining solution	5–10 min	Displays nuclear membrane, chromatin, and nucleoli	Use quality control slides to calibrate staining time
Differentiation	1% acid alcohol or 0.5% hydrochloric acid aqueous solution	4–5 s or approximately 10 s	Removes excess nuclear stain	Rinse immediately after differentiation
Bluing	Bluing solution	2 min	Stabilizes blue nuclear staining	Insufficient bluing affects nuclear color and differential staining
Dehydration before cytoplasmic staining	70% → 80% → 95% ethanol	70% and 80% for 2 min each; two 95% ethanol jars for 2 min each	Adjusts the slide to the cytoplasmic staining environment	Ethanol contamination can cause unstable differential staining
OG6 primary staining	Orange G6 staining solution	2 min	Displays keratinized cytoplasm and eosinophilic structures	Fully remove excess stain with 95% ethanol after staining
EA36 counterstaining	EA36 staining solution	3–5 min	Produces cytoplasmic differential staining in cervical cells	Do not overprocess with 95% ethanol after staining
Final dehydration and clearing	Absolute ethanol, xylene	Ethanol 1 min each; xylene approximately 2 min each	Obtains a transparent slide suitable for mounting	Water carryover can cause fogging or insufficient clearing

4 Staining Results and Acceptance Criteria

4.1 Cell Nuclei

(1) In acceptable preparations, cell nuclei should appear blue to dark blue, with clear nuclear boundaries and distinguishable nucleoli and chromatin granules.

(2) If nuclear staining is too light, nuclear details in atypical cells may be underestimated; if nuclear staining is too dark, fine granular chromatin and nuclear membrane irregularities may be obscured.

4.2 Cytoplasmic Differential Staining

(1) Keratinized cells should appear predominantly orange-yellow, indicating effective OG6 primary staining and no excessive decolorization during subsequent ethanol treatment.

(2) Superficial squamous epithelium, intermediate squamous epithelium, columnar epithelium, and inflammatory background should show distinguishable color tones. When EA36 differential staining is insufficient, the cytoplasm often appears pale, grayish, or poorly layered.

(3) If the entire slide appears overly red, overly blue-green, or shows an imbalanced overall color, EA36 staining time, 95% ethanol rinsing time, and staining solution condition should be reviewed first.

4.3 Background and Transparency

(1) The background should be clean. Mucus, inflammatory cells, and red blood cells should not significantly obscure epithelial nuclear structures.

(2) When transparency is insufficient, the slide appears gray or foggy, and the layering in overlapping cell areas becomes poor. In this case, check whether absolute ethanol contains water, whether xylene is turbid, and whether the mounting medium is suitable.

Table 2 Interpretation points for EA36 cervical cytology staining results

Observation Target	Acceptable Appearance	Abnormal Indication
Cell nuclei	Blue to dark blue, with clear nuclear membrane and chromatin	Too light suggests insufficient nuclear staining or excessive differentiation; too dark suggests insufficient differentiation
Keratinized cytoplasm	Clear orange-yellow color, without extensive orange floating stain in the background	Excessive color intensity is often related to OG6 overstaining or insufficient removal of excess stain with 95% ethanol
Non-keratinized squamous epithelium	Layered pink, blue-green, or green tones	Overall grayish color is often related to hematoxylin residue, EA36 imbalance, or poor ethanol control
Columnar epithelium and background	Distinguishable color differences from squamous epithelium and inflammatory cells	Overly dark background reduces the efficiency of abnormal cell recognition
Slide transparency	Cell contours remain visible in overlapping areas	Fogging is usually related to insufficient dehydration or clearing

5 Key Control Points

5.1 Wet Fixation and Cell Adhesion

(1) Cervical cytology preparations are sensitive to fixation timing. Air drying affects nuclear staining, cytoplasmic transparency, and EA36 differential staining simultaneously.

(2) If cell adhesion is weak in liquid-based preparations, excessive running-water rinsing and unnecessary prolonged ethanol treatment should be avoided. The same batch of samples should maintain consistent fixation and transfer timing.

5.2 Differentiation and Bluing

(1) Differentiation time should be controlled at the second level and should not be roughly extended by visual judgment. Insufficient differentiation causes overly dark nuclei and grayish-purple cytoplasm; excessive differentiation weakens nuclear details.

(2) Insufficient bluing results in unstable nuclear color and may affect the overall EA36 tone. After bluing, slides must be thoroughly rinsed to avoid alkaline residue interfering with cytoplasmic staining.

5.3 EA36 Staining and Ethanol Rinsing

(1) EA36 staining time is usually controlled at 3–5 min. Laboratory experience with EA50 or EA65 should not be directly applied.

(2) The 95% ethanol treatment after EA36 both removes excess floating stain and changes the overall cytoplasmic tone. Insufficient treatment causes a dark background, while excessive treatment results in pale cytoplasm or loss of differential staining.

(3) Cervical preparations within the same batch should preferably use the same batch of EA36, the same staining time, and the same transfer rhythm to reduce batch-to-batch color differences.

6 Common Problems and Troubleshooting

Table 3 Common troubleshooting for Papanicolaou EA36 cervical cytology staining

Problem	Main Cause	Corrective Direction
Nuclear staining too light	Insufficient hematoxylin time; excessive differentiation; drying before fixation	Extend nuclear staining or shorten differentiation; confirm fixation workflow; recalibrate with quality control slides
Nuclear staining too dark	Hematoxylin overstaining; decreased differentiation solution effectiveness; delayed rinsing after differentiation	Shorten nuclear staining or replace differentiation solution; control differentiation time and rinse immediately with running water
Overall cytoplasm too pale	Insufficient EA36 staining; excessive treatment with 95% ethanol or absolute ethanol; aged staining solution	Extend EA36 to the validated upper limit; shorten post-staining ethanol treatment; replace or filter staining solution
Cytoplasm grayish-purple	Excess hematoxylin residue; insufficient differentiation; inadequate bluing or washing	Optimize differentiation and rinsing; check bluing solution; reduce nuclear stain interference with cytoplasmic staining
Background too dark	EA36 overstaining; insufficient removal of excess OG6 or EA36; heavy mucus or blood background	Shorten EA36 time; enhance removal of excess stain with 95% ethanol; improve slide preparation and sample pretreatment
Poor differential staining layers	Unstable EA36 staining solution; contaminated ethanol gradient; inconsistent within-batch transfer rhythm	Replace ethanol gradient; confirm EA36 with quality control slides; standardize within-batch operation rhythm
Slide fogging	Water in absolute ethanol; turbid xylene; insufficient clearing or abnormal mounting medium	Replace absolute ethanol and xylene; extend clearing until acceptable; remount and evaluate
Cell detachment	Insufficient adhesion in liquid-based preparation; excessive hydration or rinsing; insufficient fixation	Optimize slide adhesion; reduce rinsing intensity; confirm fixation time and fixative coverage

7 Quality Control and Records

7.1 Quality Control Slide Setup

(1) After replacing hematoxylin, OG6, EA36, differentiation solution, or bluing solution, it is recommended to stain quality control slides first and confirm nuclear staining intensity and cytoplasmic differential staining before processing formal samples.

(2) Quality control slides should contain keratinized cells, non-keratinized squamous epithelial cells, columnar epithelial cells, and certain background components to allow simultaneous evaluation of the overall tones produced by OG6 and EA36.

7.2 Within-Batch Consistency Records

(1) Record fixation time, hematoxylin staining time, differentiation method, bluing time, OG6 time, EA36 time, and replacement dates of ethanol and xylene.

(2) When systematic color deviation occurs in the same batch, troubleshooting should first focus on staining reagent batch, ethanol gradient, differentiation solution effectiveness, and operation rhythm.

8 Reagent and Material Selection for Papanicolaou EA36 Cervical Cytology Staining

Table 4 Reagent and material selection for Papanicolaou EA36 cervical cytology staining

Cat. No.	Product Name	Grade and Purity	Corresponding Step	Use
P1511562	Papanicolaou Stain Solution (Papanicolaou EA36)	BioReagent,Biological Stain,for microscopy	EA36 counterstaining	Directly matches the theme of this protocol; used for EA36 cytoplasmic differential staining in cervical cytology
E1520384	EA36 Staining Solution	BioReagent,Biological Stain,for microscopy	EA36 counterstaining	Used for cytoplasmic counterstaining and differential staining control in the EA36 system
O1520397	Orange G6 Staining Solution	BioReagent,Biological Stain,for microscopy	OG6 primary staining	Used for primary staining of keratinized cells and eosinophilic structures
M774769	Mayer hematoxylin staining solution	BioReagent, Biological Stain, for microscopy	Nuclear staining	Can be used for the nuclear staining step in cervical cytology
I1507737	Improved Harris Hematoxylin Staining Solution	BioReagent,Suitable for microbiology,for microscopy	Nuclear staining	Can serve as a validated nuclear staining option
G774770	Hematoxylin Staining Solution (Gill No.1)	BioReagent, Biological Stain, for microscopy	Nuclear staining	Suitable for a milder routine nuclear staining system
G774771	Hematoxylin Staining Solution (Gill No.2)	BioReagent, Biological Stain, for microscopy	Nuclear staining	Suitable for routine nuclear staining in cervical cytology
G774772	Hematoxylin Staining Solution (Gill No.3)	BioReagent, Biological Stain, for microscopy	Nuclear staining	Suitable for systems requiring stronger nuclear staining
L1507847	Lithium Carbonate Saturated Aqueous Solution	BioReagent,for microscopy,Biological Stain	Bluing	Used for hematoxylin bluing
L1507846	Lithium Carbonate Aqueous Solution (0.05%)	BioReagent,Biological Stain,for microscopy,0.05%	Bluing	Used for mild bluing treatment
A1507829	Ammonia Solution (0.1%)	BioReagent,Biological Stain,for microscopy,0.1%	Bluing	Can be used as an ammonia bluing system
W274329	Water	for biotechnology nuclease-free, sterile	Rinsing/solution preparation	Can be used as standardized experimental water
X112051	Xylene	Premium-Grade Reagents, ≥99%, xylene isomer and ethyl benzene	Clearing	Used for final clearing treatment
X139941	Xylene	Anhydrous Grade, ≥98%, mixture of isomers	Clearing	Can be used for routine clearing steps
X112054	Xylene	ACS, ≥98.5%, isomers plus ethylbenzene	Clearing	Suitable for clearing in standardized experimental systems
N116470	Neutral gum	FMP	Mounting	Used for coverslip mounting

For more related articles, please see below:

[1] Papanicolaou's Stain