Blood stains

In old blood stained fibre, blood grouping is done by :

 

a.        Benzidine Test                                                            

b.        Acid Elution Test

c.        Precipitin Test                                                              

d.        Hemin Crystal Test

 

I. Benzidine Test (No longer used as Benzidine is Carcinogenic) 

    • Most reliable chemical test for blood.

    • Add a drip of saturated solution of benzidine glacial acetic acid and then a drop of 10 volumes hydrogen peroxide.

    • If blood is present, dark blue colour is produced immediately.

    • A positive reaction is given by blood of almost any age, blood that has been exposed to heat or cold. It detects blood when present in a dilution of one part of blood in 300000. 

 

II  Precipitin test

• Precipitin test–This determines whether the blood is derived from human beings or from a lower animal.• Precipitin test +ive in dead body up to 10 years

 

III. Haemin crystal test

 

 • Brownish-black rhombic crystals of haemin or haematin chloride arranged singly or in clusters are seen if blood is present

• Teichman’s Test is negative if stain is old 

 

IV:   Acid Elution Test : 

Why Acid Elution Test is used for old stains?

 

To remove antibody from coated red cells.

Red cells coated with antibody are thoroughly washed to remove unbound

protein, using a special wash solution to maintain the association of bound

antibody. The washed cells are then suspended in a low pH solution (Acid

Eluting Solution) to dissociate the bound antibody. After centrifugation, the

supernatant containing any dissociated antibody is separated from the red

cells and buffered by the addition of a buffering solution (Base Buffering

Solution).

 

The eluate is then ready to be used in antibody detection ( Blood Group)  or

identification.