Re-Evaluation of the Normal Range of Serum Total CO2 Concentration

Abstract

A reliable determination of blood pH, PCO, and [HCO] is necessary for assessing the acid-base status of a patient. However, most acid-base disorders are first recognized through abnormalities in serum total CO concentration ([TCO]) in venous blood, a surrogate for [HCO]. In screening patients on the basis of serum [TCO], we have been concerned about the wide limits of normal for serum [TCO], 10-13 mEq/L, reported by many clinical laboratories. Indeed, we have encountered patients with serum [TCO] values within the lower or upper end of the normal range of the reporting laboratory, who subsequently were shown to have a cardinal acid-base disorder.Here, we present a patient who had a serum [TCO] within the lower end of the normal range of the clinical laboratory, which resulted in delayed diagnosis of a clinically important "hidden" acid-base disorder. To better define the appropriate limits of normal for serum [TCO], we derived the expected normal range in peripheral venous blood in adults at sea level from carefully conducted acid-base studies. We then compared this range, 23 to 30 mEq/L, to that reported by 64 clinical laboratories, 2 large commercial clinical laboratories, and the major textbook of clinical chemistry. For the most part, the range in the laboratories we queried was substantially different than that we derived and that published in the textbook, with some laboratories reporting values as low as 18-20 mEq/L and as high as 33-35 mEq/L. We conclude that the limits of values of serum [TCO] reported by clinical laboratories are very often inordinately wide and not consistent with the range of normal expected in healthy individuals at sea level. We suggest that the limits of normal of serum [TCO] at sea level be tightened to 23-30 mEq/L. Such correction will ensure recognition of the majority of "hidden" acid-base disorders.

Association of blood bicarbonate and pH with mineral metabolism disturbance and outcome after kidney transplantation

“…Although the latter has been used more extensively to define metabolic acidosis in CKD patients, both parameters have been shown to associate with outcomes in large cohorts . Blood gas has been recently proposed as a confirmatory test to diagnose acid‐base disorders in patients with CKD, but both techniques have specific pitfalls and distinct normal ranges. Currently, it remains unclear if one parameter is a superior predictor of renal outcome than the other.…”

“…In fact, low total CO 2 levels may be associated with either acidemia in uncompensated metabolic acidosis, normal pH, or even elevated pH in uncompensated respiratory alkalosis. In addition, the arterial or venous origin of the blood used for the analysis also affects the bicarbonate concentration; arterial blood displays lower bicarbonate concentration than venous blood . This point may be of importance in KTR, as arteriovenous fistulae (AVFs) are frequently, but not systematically used for blood collection in this population, depending on transplantation center policies.…”

Re-Evaluation of Total CO₂ Concentration in Apparently Healthy Younger Adults

“…On the basis of an analysis of carefully conducted studies on acid-base composition of normal subjects, we recently proposed that the reference range of serum [TCO 2 ] in venous blood at sea level be narrowed to 23-30 mEq/L [4]. The results of the present study provide strong validation of the proposed range in that 91% of the serum [TCO 2 ] of apparently healthy younger adults residing at sea level were within the 23-30 mEq/L limits ( Table 2 and Fig.…”

“…In a recent publication [4], we first derived the expected reference range of serum [TCO 2 ] in venous blood in adults at sea level by analyzing carefully conducted studies on acid-base composition of normal subjects. We then compared this range to that reported by the clinical laboratories of 64 hospitals in the United States and 2 large commercial clinical laboratories, as well as the reference range endorsed by the American Association of Clinical Chemistry and that listed in the Tietz Textbook of Clinical Chemistry and Molecular Diagnostics [5], the major clinical chemistry textbook.…”

Dialysate bicarbonate concentration: Too much of a good thing?

“…The physiologic approach to assessing acid‐base status views blood pH as being determined by the prevailing levels of carbonic acid (that is, PCO 2 , the respiratory component) and HCO 3 − (the metabolic component, further indicated as BIC) . The standard blood gas analyzer measures pH and PCO 2 , from which BIC is calculated using the Henderson Hasselbalch equation .…”