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The Sahli method, also referred to as the acid hematin method, is a technique used to measure the amount of haemoglobin in blood. In this process, blood is mixed with a dilute solution of hydrochloric acid (HCl) to convert hemoglobin into a brown-colored substance called acid hematin. The resulting solution is then diluted until its color matches that of a standard brown glass. The hemoglobin value is then read directly from a scale.
Hemoglobin is the iron-containing metalloprotein in Red blood cells (RBCs) that transports oxygen. It is responsible for the red pigmentation of red blood cells.
The test is commonly performed by clinical/ medical laboratory technicians for the clinical investigation of Anemia.
Sahli method principle
When blood is added to hydrochloric acid, the hemoglobin in red blood cells is converted to acid hematin which is dark brown.
The concentration of color formed is directly proportional to the concentration of hemoglobin present.
A reference brown glass in the Sahli setup is used. The mixture is then diluted with HCl or distilled water until the color matches that of the reference tube.
Sahli acid test requirements
- N/10 hydrochloric acid
- Distilled water
- Sahli apparatus
- Glass rod
- Specimen – blood
Sahli method procedure
- Put hydrochloric acid into the Hb tube up to the ’20’ mark.
- Dispense 20 microlitres of blood into the tube using a pipette.
- Leave the tube at room temperature for 10 minutes to allow for the conversion of hemoglobin to acid hematin.
- Place the tube into the Sahli comparator box.
- Dilute the mixture with distilled water or hydrochloric acid drop-wise while stirring.
- Stop adding the moment the color of the mixture matches that of the comparator tube.
- Note the reading on the lower meniscus of the hemoglobin tube.
The readings are marked and expressed as gram/dl.
