Table 5:

Interferences in parameters and methods

Parameter, method Aspartataminotransf erase (AST)	Comments The activity of AST in erythrocytes is 40x higher than in plasma. In patients with AST activities in the reference range haemolysis with haemoglobin values of 1.5 g/L causes an elevated AST activity.
Bilirubin	False low concentrations are measured using the Jendrassik-Gróf-method, because the pseudoperoxidase activity of haemoglobin inhibits the formation of the azo dye. The inhibition can be observed if the free haemoglobin concentration in serum is higher than 0,8 g/L12.
Creatinkinase (CK)	Released erythrocyte adenylkinase increases the enzymatically measured CK- and CK-MB activities. Adenylatkinase added to the chemical reaction mixture cannot be inhibited through AMP and diadenosinpentaphospate. Consequently there is an increase in the measurement signal.
Fe (iron)	Potentially haemoglobin is a huge source for iron. However, the additive iron effect is insignificant14, because the iron-porphyrin binding is stronger than the iron-transferin binding and methods for the determination of iron only measure iron released from transferrin.
Total protein	The additive effect of haemoglobin on the total protein concentration is small, but significant.
Uric acid	Only high haemoglobin concentrations cause lower serum values. The uricase-catalase method (Kageyama-reaction) is more susceptible to interference than the uricase-peroxidase method.
Potassium	The concentration of potassium in red blood cells is approximately 25 x higher than in plasma. The concentration of potassium is increased, even if the in vitro haemolysis is not visible through red coloration. This can be noticed if a whole blood sample with low glucose values is stored several hours at room temperature.
Inorganic phosphate	Blood cells have a high phosphate level, but the major part is organically bound. The addition of organic phosphate esters to serum can produce a release of inorganic phosphate that can falsely increased phosphate concentrations. For this reason serum should be separated from erythrocytes within 2 hours after specimen collection.
Serum proteinelectrophoresis	Haemoglobin-haptoglobin-complexes move between the α2- and ß-Globulin fractions. Free haemoglobin migrates as a diffuse reddish band in the ß-globulin fraction.
Immunoassays	Immunoassays are evaluated by diagnostic kit manufacturers for interferences to haemolysis in the same way as other clinical chemistry tests. However, the manufacturers often only add haemoglobin (mostly human methemoglobin is used) to samples. When suspecting an haemolysis interference factor of an immunoassay haemoglobin should not be confused with haemolysis. Blood cells contain components other than haemoglobin that can hamper immunoassays. Therefore, it is very important to ask the product manufacturer how haemolysis testing was performed.