Explanation of the Decrease in Alkaline phosphatase (ALP) Activity in Hemolysed Blood Samples from the Clinical Point of View: In vitro study

Hemolysis is still the most common reason for rejecting samples, while reobtaining a new sample is an important problem. The aim of this study was to explain the decrease in the activity of Alkaline phosphatase (ALP) enzyme after hemolysis of blood samples and whether conversion of zinc and magnesium ions to inhibit alkaline phosphatase activity after they released from red blood cells. Twenty healthy volunteers were enrolled in the study. Four hemolysis levels were constituted according to hemoglobin concentrations (0.02, 0.27 ,0.75 and 3.34 g/L). Non–hemolysed samples was obtained from each volunteer and considered as control. Hemolysis was achieved by mechanical trauma. Alkaline phosphatase activity and the concentrations of zinc and magnesium ions were measured in the hemolysed and non-hemolysed samples. Ten non-hemolysed serum samples (Hb concentration was 0.02 g/L) were divided into two groups samples A and B. ALP activity was measured in these samples. In vitro study was carried out including the addition 68.3 mg/dL of magnesium chloride to group A and 5.1 μg/dL of zinc chloride to group B. ALP activity was measured in the sera of the two groups. The significant decrease (p 0.001) in ALP activity was observed at moderate (13.2 ± 7.2IU/L), and severe hemolysis (5.5± 2.3IU/L) compared with that in non hemolysed samples. In these levels of hemolysis the concentrations of Zn+2ions (5.1 ±1.1μg/dL) and Mg+2ions (68.3± 8.6mg/dL) were significantly increased (p 0.01) compared with their concentrations in non-hemolysed samples. Alkaline phosphatase activity was inversely proportional with the increase in the hemoglobin concentrations in the hemolysed samples. A significant decrease (p 0.005) in the activity of ALP was observed after the addition of 68.3.0 mg/dl of magnesium chloride to group A. There was no significant decrease (p 0.1) in activity of ALP in the samples of group B. The findings of this study indicate that blood cell hemolysis reduces the activity of ALP which is directly proportional to the level of hemolysis. Released Mg+2 ions were found to inhibit ALP activity in the blood hemolysed samples