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 Table of Contents  
Year : 2016  |  Volume : 13  |  Issue : 2  |  Page : 45

Discrepancies in interlaboratory plasma bicarbonate measurement

The Editor-in-Chief, Journal of Clinical Sciences, The Office of the Dean, Faculty of Clinical Sciences, College of Medicine, University of Lagos, PMB 12003, Idi Araba, Lagos, Nigeria

Date of Web Publication4-Apr-2016

Correspondence Address:
Elaine Chinyelu Azinge
The Editor-in-Chief, Journal of Clinical Sciences, The Office of the Dean, Faculty of Clinical Sciences, College of Medicine, University of Lagos, PMB 12003, Idi Araba, Lagos
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2408-7408.179647

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How to cite this article:
Azinge EC. Discrepancies in interlaboratory plasma bicarbonate measurement. J Clin Sci 2016;13:45

How to cite this URL:
Azinge EC. Discrepancies in interlaboratory plasma bicarbonate measurement. J Clin Sci [serial online] 2016 [cited 2020 Aug 9];13:45. Available from: http://www.jcsjournal.org/text.asp?2016/13/2/45/179647

The bicarbonate content of plasma is a significant indicator of the buffering capacity of that individual. Bicarbonate is the second, largest fraction of the anions of plasma, [1] measured as these fractions are bicarbonate, carbon dioxide in solution, and carbimino compounds. [1],[4] The reference range of bicarbonate is 22-29 mmol/L. [2],[3] Together with hydrogen concentration, bicarbonate is used in the diagnosis of serious disorders of acid-base balance in clinical medicine. [1],[4] These are disorders that affect the respiratory and metabolic systems of the body. Important causes of acid-base dysfunction include diarrhea, chronic renal failure, diabetic ketoacidosis, and renal tubular acidosis. [4]

Quite often in this locality, requests from the same patient are sent to different laboratories for analysis and often enough discrepancies often arise in the measurement of plasma bicarbonate, especially in pediatric patients where the volume of drawn blood is low. [5] The practice of sending the same sample to different laboratories arose in recent times as a result of poor funding and infrastructural decay found in government laboratories and its attendant consequences. For this reason, it is important to highlight preanalytical causes of discrepancies in bicarbonate measurements. [6],[7],[8] Phlebotomy errors cause 24-30% of serious patient misdiagnosis. Inadequate filling of specimen tubes which usually occurs in pediatric subjects causes a significant decline in bicarbonate measurement known as pseudometabolic acidosis. The cause of this is inadequate anticoagulant/blood ratio. [6],[9] Also, because the determination of bicarbonate includes dissolved carbon dioxide, this fraction will escape into the air once the stopper of the specimen bottle is removed from the sample tube. The escape of carbon dioxide can cause a decrease of up to 6 mmol/L in the course of 1 h. [1],[4]

Separated plasma should not be left at 15-30°C for longer than 8 h. [1] The sample must be stored at 2-8°C if it is going to be stored for longer than 48 h and should be thawed only once. Analyte deterioration is usually found in repeatedly thawed and frozen samples. [1] If the logistics in different laboratories are different, the extent of error will be different. These are some of the causes of discrepancies in results from the same patient analyzed in different laboratories. [4]

Discrepancies can also arise as a result of the choice of methodology. [10] There are titrimetric, enzymatic, and calculated methods of measuring bicarbonate. [5],[10] Different laboratories adopt different methods depending on how well funded the laboratory is.

The reference ranges of bicarbonate differ with age:

  • 0-7 days is 13-26 mmol/L
  • 7 days-15 years is 20-30 mmol/L
  • >15 years is 22-29 mmol/L [1],[4]
  • Critical call results are values <10 mmol/L or >40 mmol/L
  • These must be sent urgently to the consulting physician. [1]

  References Top

Bicarbonate in Refrigerated Serum NHANES 2003-2004. Collaborative Laboratory Services L.L.C. Available from: http//www. cdc.gov/nchs/data/nhanes/nhanes/01_02/140b_met_bicarbonate pdf. [Last accessed on 2015 Dec 23].  Back to cited text no. 1
Reed AH, Henry RJ, Mason WB. Influence of statistical method used on the resulting estimate of normal range. Clin Chem 1971;17:275-84.  Back to cited text no. 2
Herrera L. The precision of percentiles in establishing normal limits in medicine. J Lab Clin Med 1958;52:34-42.  Back to cited text no. 3
Tietz NW. Textbook of Clinical Chemistry. Philadelphia, PA: W.B. Sanders; 2015.  Back to cited text no. 4
Ungerer JP, Ungerer MJ, Vermaak WJ. Discordance between measured and calculated total carbon dioxide. Clin Chem 1990;36:2093-6.  Back to cited text no. 5
Cuhadar S. Preanalytical variables and factors that interfere with biochemical parameters. A review. OA Biotechnol 2013;2:19.  Back to cited text no. 6
Herr RD, Swanson T. Pseudometabolic acidosis caused by underfill of vacutainer tubes. Ann Emerg Med 1992;21:177-80.  Back to cited text no. 7
Narayanan S. The preanalytic phase. An important component of laboratory medicine. Am J Clin Pathol 2000;113:429-52.  Back to cited text no. 8
Kumar V, Karon BS. Comparison of measured and calculated bicarbonate values. Clin Chem 2008;54:1586-7.  Back to cited text no. 9
Forrester RL, Wataji LJ, Silverman DA, Pierre KJ. Enzymatic method for determination of CO2 in serum. Clin Chem 1976;22:243-5.  Back to cited text no. 10


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