Periodic acid schiff (PAS) stain test

PAS stain can be used for multiple clinical reasons. These include:

• Evaluation of glycogen deposits in the liver
• Diagnosing tumours of bladder, kidney, liver, pancreas, ovary and lungs, as they may contain glycogen granules
• Detection of fungal infections as fungal cell walls have a high carbohydrate content

PAS stain is also used to look for abnormalities in the basement membranes - a thin layer of fibrous tissue that separates body’s outer layer and internal structures from the underlying tissues. These are present at various locations throughout the body. Basement membrane abnormalities detected by PAS staining can help in the diagnosis of several disorders. Examination of the basement membranes can also be done to measure the invasiveness of skin tumours.

The PAS stain may be used in combination with a diastase stain for specifically identifying glycogen granules and differentiating glycogen from other PAS stain positive tissue elements.

This stain may also be routinely used for diagnosing inflammatory skin diseases.

For this staining procedure, your doctor will require a sample of the concerned tissue, which will be taken by a procedure called biopsy. 

Before the biopsy, you must make sure to discuss with your doctor any health conditions you have and any medications or supplements you may be taking, such as: 

• Antidepressants
• Antibiotics 
• Asthma medications
• Blood-thinning medications
• Blood pressure medications 
• Diabetes medications 
• Pain killers including nonsteroidal anti-inflammatory drugs and aspirin

Your doctor may instruct you to fast for eight hours before the test. 

For safety reasons, you may be advised to arrange for a ride home after the biopsy. In certain cases, your doctor may ask you to be admitted to the hospital for the procedure.

• You may be provided with a gown to change into before the procedure. 
• Your doctor will give you a sedative through a vein - if needed - so that you can relax. If a skin biopsy is being performed, the doctor will use a local anaesthetic to numb the area. 
• A tissue sample will be taken from the concerned organ through a small surgery, punching a small hole through the concerned tissue or with the use of a fine needle.
• The collected sample will then be sent to the laboratory for further analysis.

There can be certain risks associated with biopsies. In case of a skin biopsy, you may notice a small rim of redness at the edge of the healing biopsy site, which goes away gradually. If you notice increasing redness, pus or significant pain, please inform your doctor. It may take up to three weeks for the biopsy site to heal completely.

Other general risks associated with biopsy are:

• Bleeding 
• Infection
• Accidental injury to the neighbouring structures/organs

The biopsied area is likely to remain sore for a few days.

Normal results:

In a typical staining procedure with the PAS stain, the glycogen, fungi and basement membranes appear pink or red.

The nuclei will appear blue if haematoxylin dye is used as a counterstain or green if light green stain is used.

Abnormal results:

An abnormal result on PAS stain could be attributed to conditions such as:

• Fungal infections caused by organisms such as Aspergillus fumigatus, Candida albicans and Cryptococcus neofarmans
• Tumours of the bladder
• Tumour of kidney, liver, pancreas 
• Skin tumour
• Glycogen storage disease
• Lupus-associated kidney disease

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.