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Direct bilirubin higher than total bilirubin?

CASE DESCRIPTION

A 77-year-old man with multiple myeloma and recent cholecystostomy tube placement presented to the emergency department with pneumonia. His cholecystostomy tube was noted to be clamped shut. Total and direct serum bilirubin measurements were 0.2 and 1.66 mg/dL, respectively. Dilutions of the specimen were made, and the results are listed in Table 1.

Table 1. Bilirubin measurements at various
dilutions.

Dilution   Bilirubin, mg/dL

           Total   Direct

None        0.2     1.66
1:3         0.3     0.11
1:6         0.3     0.29
1:11        0.3     0.03

QUESTIONS

1. How does the analysis of direct bilirubin differ from that of total bilirubin?

2. Can direct bilirubin ever be greater than total bilirubin?

3. What are the possible explanations for the results?

The answers are below.

Answers

Both total and direct bilirubin measure the formation of azobilirubin, which is detected at 570/660 nm. The total bilirubin reaction contains surfactant and caffeine, which solubilize "indirect" bilirubin and accelerate the reaction (1). Direct bilirubin is a component of total bilirubin and therefore should always be smaller in value. The presence of a monoclonal immunoglobulin (2220 mg/dL) falsely increased the direct, but not the total, bilirubin measurement. Hemolysis and lipemia can also interfere at high concentrations (2).

Author Contributions: AH authors confirmed they have contributed to the intellectual content of this paper and have met the following 3 requirements: (a) significant contributions to the conception and design, acquisition of data, or analysis and interpretation of data; (b) drafting or revising the article for intellectual content; and (c) final approval of the published article.

Authors' Disclosures or Potential Conflicts of Interest: No authors declared any potential conflicts of interest.

References

(1.) Burtis CA, Ashwood ER, Bruns DE. Tietz textbook of clinical chemistry and molecular diagnostics. 5th edition. Philadelphia: Saunders; 2012.

(2.) Direct and total bilirubin on Beckman Coulter AU analyzers [Package insert]. Brea (CA): Beckman Coulter; August 2012.

Matthew Ball, Irene Miller, and Steven W. Cotten *

Department of Pathology, Ohio State University Wexner Medical Center, Columbus, OH.

* Address correspondence to this author at: Department of Pathology, Ohio State University Wexner Medical Center, 4164 Graves Hall, 333 W. 10th Ave., Columbus, OH 43210. E-mailsteven.cotten@osumc.edu.

Received December 6, 2014; accepted December 18, 2014.

DOI: 10.1373/clinchem.2014.237040

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Article Details
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Title Annotation:What Is Your Guess?
Author:Ball, Matthew; Miller, Irene; Cotten, Steven W.
Publication:Clinical Chemistry
Article Type:Clinical report
Date:Jun 1, 2015
Words:384
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