Question

Benjamin, a 39-year-old male, was seen in the emergency department following a possible grand mal seizure. He informed the physician that he had been taking therapeutic doses of phenobarbital and phenytoin for several months. The doctor ordered drug levels for each compound. A phlebotomist drew a blood sample in a red-top tube that contained serum separator gel. Results of the laboratory tests are shown below:

Test	Result	Therapeutic range
Phenobarbital (μg/mL)(μg/mL)	4.0	15–30
Phenytoin (μg/mL)(μg/mL)	3.5	10–20

The physician questioned the laboratory’s results and asked for a repeat analysis.

Issues and Questions to Consider

1. Are these results consistent with Benjamin’s history?

2. Are the laboratory results incorrect? If so, what is the source of the error?

3. Does the laboratory need to repeat the analysis?

4. What course of action should the laboratory follow to prevent future questioning of these assays?

Answer 1

Are these results consistent with Benjamin’s history?

No. these results are not correlated with Benjamin's history. He is taking phenobarbital and phenytoin for several months. So there is a more chance for an increased level of drug in the blood. But the test results show below the therapeutic range.

Are the laboratory results incorrect? If so, what is the source of the error?

The laboratory results are incorrect because the test tube contains serum separator Gel.

Does the laboratory need to repeat the analysis?

Yes. the laboratory needs to repeat the analysis by collecting the sample in a red plain tube without any gel.

What course of action should the laboratory follow to prevent future questioning of these assays?

The Laboratory should develop the protocols and should be followed by technicians to prevent such errors in the future. The lab incharge should assess the variables that interfere with the test results and quality of test periodically