To the Editor:

We read with great interest the article by Dr. Kertai et al.,1  in which the authors identified a novel association between postoperative nadir platelet counts and acute kidney injury (AKI) and short-term mortality after coronary artery bypass grafting surgery. Despite the elaborate statistical analysis and the innovative perspectives, we are profoundly concerned with the study design and the interpretation of statistical results, which we expect the authors to comment on and address.

First, we consider perioperative blood loss as a crucial confounding variable that should not be overlooked in the study design, nor be absent from the logistic regression analysis of AKI and mortality predictors. Significant blood loss is well established in previous literatures, poses major challenges in many cardiac surgeries, and has been identified as having strong, independent association with postoperative in-hospital mortality and AKI.2–5  Furthermore, the concomitant decrease in platelet counts and serum hemoglobin in this study is also a strong indicative of significant perioperative blood loss, which very much likely was the true underlying cause of both AKI and short-term mortality. Therefore, it is of crucial importance that all relevant predictors, especially such important predictor as perioperative blood loss, be included in the logistic regression analysis. However, according to the authors, they were not able to investigate the influence of postoperative bleeding due to the retrospective nature of the study, which we readers hesitate to give our full trust given the requirements of comprehensive intensive monitoring postcardiac surgeries. Hence, before the effect of perioperative blood loss on AKI is conclusively affirmed, we readers should be highly cautious about the conclusions this study attempted to present, i.e., the novel association between thrombocytopenia and postoperative AKI. Such conclusions may be distracting, if not misleading, to us readers, since the association between perioperative blood loss and AKI may be concealed behind the seemingly causative thrombocytopenia. We, therefore, suggest that the authors and interested readers focus more attention on perioperative blood loss, rather than platelet reduction, in the future researches of postoperative AKI.

Second, previous studies have verified that coagulation factor and fibrin dysfunctions are also in significant association with postoperative kidney and myocardial injuries.6,7  Therefore, we advise the authors to explore the functions of the whole set of serum coagulant components on AKI from a broader view, other than focusing on the single variable of platelet count.

In summary, we applaud Dr. Kertai et al. for their enlightening study and opinions on AKI and short-term mortality after cardiac surgeries. However, it is of utmost importance for us readers to keep alerted of the conclusions this study intended to present, in order to avoid overreliance on the statistical results while neglecting the possible biologic implausibility. We expect the authors to further address and explore on the above issues.

Competing Interests

The authors declare no competing interests.

References

1.
Kertai
MD
,
Zhou
S
,
Karhausen
JA
,
Cooter
M
,
Jooste
E
,
Li
YJ
,
White
WD
,
Aronson
S
,
Podgoreanu
MV
,
Gaca
J
,
Welsby
IJ
,
Levy
JH
,
Stafford-Smith
M
,
Mathew
JP
,
Fontes
ML
:
Platelet counts, acute kidney injury, and mortality after coronary artery bypass grafting surgery.
Anesthesiology
2016
;
124
:
339
52
2.
Karkouti
K
,
Wijeysundera
DN
,
Yau
TM
,
Beattie
WS
,
Abdelnaem
E
,
McCluskey
SA
,
Ghannam
M
,
Yeo
E
,
Djaiani
G
,
Karski
J
:
The independent association of massive blood loss with mortality in cardiac surgery.
Transfusion
2004
;
44
:
1453
62
3.
Goren
O
,
Matot
I
:
Perioperative acute kidney injury.
Br J Anaesth
2015
;
115
(
suppl 2
):
ii3
14
4.
Walsh
M
,
Garg
AX
,
Devereaux
PJ
,
Argalious
M
,
Honar
H
,
Sessler
DI
:
The association between perioperative hemoglobin and acute kidney injury in patients having noncardiac surgery.
Anesth Analg
2013
;
117
:
924
31
5.
Brienza
N
,
Giglio
MT
,
Marucci
M
,
Fiore
T
:
Does perioperative hemodynamic optimization protect renal function in surgical patients? A meta-analytic study.
Crit Care Med
2009
;
37
:
2079
90
6.
Mörtberg
J
,
Blombäck
M
,
Wallén
H
,
He
S
,
Jacobson
SH
,
Spaak
J
:
Increased fibrin formation and impaired fibrinolytic capacity in severe chronic kidney disease.
Blood Coagul Fibrinolysis
2016
;
27
:
401
7
7.
Campo
G
,
Valgimigli
M
,
Ferraresi
P
,
Malagutti
P
,
Baroni
M
,
Arcozzi
C
,
Gemmati
D
,
Percoco
G
,
Parrinello
G
,
Ferrari
R
,
Bernardi
F
:
Tissue factor and coagulation factor VII levels during acute myocardial infarction: Association with genotype and adverse events.
Arterioscler Thromb Vasc Biol
2006
;
26
:
2800
6