𝐏𝐫𝐞𝐬𝐮𝐦𝐩𝐭𝐢𝐯𝐞 𝐓𝐞𝐬𝐭 𝐅𝐨𝐫 𝐁𝐥𝐨𝐨𝐝

Introduction

• Blood is a fluid connective tissue that consists of the fluid portion (plasma) and the cellular portion (RBCs, WBCs, and platelets).
• It is one of the most important pieces of physical evidence that can link a suspect to the crime scene.
• It can be found in almost every type of criminal offense in the form of a blood droplet, pool, stain, etc.

Presumptive test

• These tests rely on the catalytic properties of the blood.
• These tests produce a color reaction, which is carried out by first applying a solution of chromogen to a sample of suspected material or stain, followed by the addition of hydrogen peroxide, which works as an oxidizing agent. 
• The heme group of Hb works as a catalyst, thus producing a rapidly developing color constituting a positive test.

Benzidine test

• The oxidation of benzidine takes place in the presence of heme as a catalyst, producing a blue to dark blue color.
• The reaction is carried out in an acidic solution.
• Benzidine was replaced by tetramethylbenzidine as it was carcinogenic.

Kastle–Meyer test

• Phenolphthalin produces a bright pink color.
• The reagent consists of reduced phenolphthalin in an alkaline solution, which is oxidized by hydrogen peroxide in the presence of heme in the blood.

Luminol Test

• Luminol is a chemiluminescent assay. It is the most sensitive.
• And is capable of detecting traces of blood in parts per million concentrations.
• In the presence of heme ax, a catalyst, the oxidative reaction of luminol produces a light that can be observed in the dark but fades easily, therefore requiring immediate photography.

Leucomalachite Green (LMG) Assay

• Malachite green is a triphenylmethane dye. 
• The leuco base form of malachite green is colorless. 
• LMG oxidation is catalysed heme to produce a green colour.

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