Volume 19 Supplement 1

35th International Symposium on Intensive Care and Emergency Medicine

Open Access

Urinary strong ion difference and acute kidney injury: an early marker of renal dysfunction?

  • P Balsorano1,
  • A De Gaudio1,
  • Stefano Romagnoli1 and
  • Ipsita Krishnan2
Critical Care201519(Suppl 1):P361


Published: 16 March 2015


Kidneys play a crucial role in the regulation of electrolytes and acid-base homeostasis. Impaired renal function is associated with greater urinary strong ion difference (SIDu) in patients with metabolic acidosis [1]. In critically ill patients, several factors, such as infused fluids and acid endogenous production, would lead to changes in plasma SID and acid-base homeostasis without renal regulation of urinary electrolytes and SIDu [2]. Hence, AKI can be highlighted as an inability to address acid-base metabolic disturbances, which may be detected before major increases in creatinine or decreases in urine output. We evaluated the effects of renal function on urinary strong ion excretion using the Stewart approach to acid-base in critically ill patients with AKI.


A retrospective study was conducted. Patients with a diagnosis of AKI according to KDIGO creatinine criteria and available urinary chemistry at one point during their ICU stay were evaluated. Day 0 was defined as the day when SIDu was calculated from urinary spot analysis (SIDu = Na+U + K+U - Cl-U). Patients were followed and staged for AKI in the next 3 days. AKI reversibility was defined according to the lack of criteria for AKI.


In total, 143 critically ill patients with a diagnosis of AKI were included. SIDu at day 0 did not differ between different AKI stages at day 0. SIDu at day 0 was statistically different between different AKI stages at days 1, 2, 3 (Table 1). SIDu at day 0 was statistically different between reversible and not reversible AKI at days 1, 2, 3 (Table 2). A conventional receiver-operating curve was generated to assess the accuracy of SIDu to predict AKI reversibility at day 1. AUC for SIDu was 0.82 (P < 0.0001; 95% CI: 0.75 to 0.88).
Table 1

SIDu (mEq/l) between different AKI stages at days 1, 2, 3 post admission.

AKI stage







Day 1

48.1 (21)

46 (22)

37.9 (20)

17.3 (22)


Day 2

40.2 (23)

45.9 (20)

45 (23)

29 (22)


Day 3

40.3 (26)`

47.2 (18)

53.2 (23)

31 (23)


Table 2

SIDu (mEq/l) between reversible versus not reversible AKI at day 1, 2, 3.



Not reversible



16.8 (23)

43.9 (21)



28.5 (24)

45.3 (22)



30 (24)

47.3 (21)



SIDu identified patients with reversible AKI with good accuracy. SIDu can be a promising, simple and cost-effective tool in AKI patient evaluation. Further research is needed to assess SIDu capability to early detect patients with renal dysfunction before increases in creatinine or decreases in urine output.
Figure 1

Group mortality, high and low chlorine.

Authors’ Affiliations

AOUC Careggi
Rhode Island Hospital


  1. Moviat M, et al: J Crit Care. 2012, 27: 255-60. 10.1016/j.jcrc.2011.05.028.View ArticlePubMedGoogle Scholar
  2. Masevicius FD, et al: Crit Care Resusc. 2010, 12: 248-54.PubMedGoogle Scholar


© Balsorano et al.; licensee BioMed Central Ltd. 2015

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.