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Ready to Settle.


A blood gas sample (Fig. 1) was sent to the laboratory from a 64-year-old male patient with stage IV non-small- cell lung cancer and paraneoplastic dermatomyositis. The results for electrolytes, glucose, pH, pC[O.sub.2], and p[O.sub.2] were unremarkable, but the instrument could not generate co-oximetry (e.g., oxyhemoglobin) results. Despite extensive mixing before analysis, the erythrocytes fully separated and settled within 3 min of sample injection. This phenomenon was not observed in a sample obtained the previous day.


1. How do you explain the unusually rapid settling of erythrocytes in this sample?

2. How are red cell separation and settling typically quantified?

3. Why was the instrument able to perform glucose, electrolyte, and some blood gas measurements, but not co- oximetry? The answers are below.


Intravenous immunoglobulin, administered to treat various immune-mediated diseases (1, 2), increases the erythrocyte sedimentation rate by generating red cell stacks known as "rouleaux" (1-4). The blood gas sample was collected just after a 2 g/kg intravenous immunoglobulin infusion. The erythrocyte sedimentation rate increased from 35 mm/h (reference interval <15 mm/h) to >145 mm/h, and rouleaux were detected in type and screen samples. The unaffected analytes are measured in the plasma fraction of whole blood, whereas co-oximetry requires lysis of erythrocytes to release hemoglobin.

Author Contributions: All authors confirmed they have contributed to the intellectual content of this paper and have met the following3 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.


(1.) Koffman BM, Dalakas MC. Effect of high-dose intravenous immunoglobulin on serum chemistry, hematology, and lymphocyte subpopulations: assessments based on controlled treatment trials in patients with neurological diseases. Muscle Nerve 1997;20: 1102-7.

(2.) Lee KY, Lee HS, Hong JH, Han JW, Lee JS, Whang KT. High-dose intravenous immunoglobulin downregulates the activated levels of inflammatory indices except erythrocyte sedimentation rate in acute stage of Kawasaki Disease. J Trop Pediatr 2005;51:98-101.

(3.) Salehzadeh F, Noshin A, Jahangiri S. IVIG effects on erythrocyte sedimentation rate in children. Int J Pediatr 2014;2014:981465.

(4.) Bedell SE, Bush BT. Erythrocyte sedimentation rate. From folklore to facts. Am J Med 1985;78:1001-9.

Zahra Shajani-Yi, Abigail A. Brunelle, and Robert D. Nerenz *

Dartmouth-Hitchcock Medical Center, Lebanon, NH.

* Address correspondence to this author at: Dartmouth-Hitchcock Medical Center, One Medical Center Drive, Lebanon, NH 03756. Fax 603-650-4845; e-mail

Received February 17,2017; accepted March 23,2017.

DOI: 10.1373/clinchem.2017.273045

Caption: Fig. 1. Sample showing erythrocytes fully separated and settled within 3 min of sample injection despite extensive mixing before analysis.

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Title Annotation:What Is Your Guess?
Author:Shajani-Yi, Zahra; Brunelle, Abigail A.; Nerenz, Robert D.
Publication:Clinical Chemistry
Article Type:Clinical report
Date:Sep 1, 2017
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