it helps to wash the hands with soap and water before taking a blood sample, otherwise if you have been handling anything greasy such as butter or fried chicken, the grease will prevent the desired hanging drop of blood from forming

also any jam or cake icing on the skin will be absorbed into the blood and cause a false high reading

with testing machines, you should take 3 readings using blood from the same hole and note the difference between the readings, ths difference is often more than you may expect

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