cohb blood test used to diagnose carboxyhemoglobin in the blood.

Carboxyhemoglobin blood test procedure

Normal blood is diluted 1:300 in a dilute ammonia solution (it prevents the precipitation of plasma proteins). It is placed in the cell of the Spectroscope.

The instrument is set in such a way that bands of oxyhaemoglobin’s spectra overlap exactly. Now the patient’s blood is diluted in the same way and placed in the spectroscopic cell in place of normal blood.

There should be disturbance of the no instrument’s adjustment for accuracy. If this test sample contains carboxyhemoglobin, there will be slight shifting of the bands.

They will no longer overlap each other and will shift towards the violet colour of the spectrum (Figure). This test will give a rough estimation of carboxy haemoglobin.

It can detect 50% or more saturation with CO. This method becomes more sensitive if the test is done in a dark room or with a green filter.

The patient’s blood is then placed and the mean read noted. Even the slightest difference in the position of the absorption band should be noted.

This method can determine 10-20% sub of Hb with CO. If a blood sample is completely saturated with CO, the shift between the bands is 60° Angstrom.

Note: A sample’s saturation with CO can be calculated according to this standard.

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