Incompatibility of total and direct bilirubin results:
A- In some cases, the cause of these changes is due to the spoilage or contamination of TB measurement solutions, which causes DB to be more than TB. However, because this problem occurs in all samples, it is diagnosed quickly.
B- The second problem is the additive interference caused by paraproteins and the turbidity caused by the lipemic serum sample.
P- Note that hemolysis always causes a false decrease in serum bilirubin. This can be important especially in babies with atresia of the bile ducts, which causes an increase in direct bilirubin.
T- The false increase of bilirubin, both total and direct, has been reported in different methods.
There are two biochemical methods to measure serum bilirubin. Dichloroaniline (DCA) and dichlorophenyldiazonium salt (DPD) method.
C- Generally, the acidity of the reaction medium and the low ionic strength of the reaction medium lead to the precipitation of paraprotein.
C- In the DCA method, the increase in paraprotein causes a false increase in direct bilirubin. which is caused by the acidity of the reaction environment and paraprotein deposition.
H- In the DPD method, total bilirubin mainly increases, which is due to the presence of solubilizing agents such as caffeine and surfactant, which are not present in the direct method.
Para-protein precipitation is not dependent on the type of error (IgM IgG) and can occur with any concentration.
D- The presence of paraprotein causes a false increase in other biochemical tests such as creatinine, urea, phosphorus, iron, and calcium.
Z- A false increase in bilirubin due to sedimentation reactions due to the use of radiographic contrast drugs has also been reported.
Interference detection method:
1- Inconsistency between direct and total bilirubin results or an increase in total bilirubin without serum ictericity.
2- Visual examination of the serum in terms of ictericity or the presence or absence of the icteric index flag in the autoanalyzer report.
3- Since it is not possible to visually check the reaction in biochemical auto analyzers, it is better to check paraprotein deposition or color formation by performing the reaction in a test tube manually. If there is turbidity, centrifuge the tube and read the sample again
4- Comparison of test results with other biochemical tests such as liver enzymes
5- Changing the test method, for example, if you use the DCA method, use the DPD or Diazo method for further investigation.
In the photo below, you can see the effect of paraprotein on total bilirubin by DPD method
Picture A is a normal sample with total bilirubin 3/3.
Image B Total bilirubin 21
Picture C, turbidity in total bilirubin measurement due to paraproteinemia
This post is written by Amer_7798