High, low hemoglobin levels without anemia predict mortality risk after CABG
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Key takeaways :
- In non-anemic patients, there is a U-shaped association between preoperative hemoglobin level and mortality after CABG.
- There is a “clear gender difference” in hemoglobin cutoffs and effects.
Higher preoperative hemoglobin levels are associated with higher mortality in both men and women after CABG, whereas patients with lower limits of normal hemoglobin levels were at greater risk compared with mid‐normal values, data show.
“Anemia can cause postoperative complications such as arrhythmia, hypoxemia and heart failure if left untreated,” Kaveh Hosseini, MD, of the Tehran Heart Center at Tehran University of Medical Sciences, Iran, and colleagues wrote in the study background. “The major adverse cardiac and cerebrovascular events rate in patients undergoing coronary artery bypass grafting with preoperative anemia is higher than in patients with normal hemoglobin concentration. Hemoglobin level variation may affect in‐hospital and midterm mortality in anemic or even nonanemic patients undergoing CABG. Although the association between preoperative anemia (based on hemoglobin level) and post‐CABG mortality has been well established before, the outcomes were not evaluated across the spectrum of hemoglobin in nonanemic patients.”
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In a registry-based, serial cross-sectional study, Hosseini and colleagues analyzed data from 13,557 adults without anemia who underwent CABG with complete follow‐up data at the Tehran Heart Center between 2005 and 2016. Patients’ hemoglobin levels were recorded before the operation as a part of the complete blood count test. The primary endpoint was in‐hospital mortality; secondary endpoints were 6‐month and 1‐year mortality. Researchers calculated sex‐specific correlations between outcomes and normal hemoglobin levels.
The findings were published in Clinical Cardiology.
Within the cohort, 134 patients died in-hospital. Preoperative hemoglobin levels were significantly lower among patients who died in-hospital; these patients also had higher rates of diabetes and hypertension, and a lower ejection fraction.
The correlation between hemoglobin level and in‐hospital mortality was nearly U‐shaped. A hemoglobin of 15.62 g/dL or higher and 13.25 g/dL or lower for men and a hemoglobin of 14.92 g/dL or higher and 13.4 g/dL or lower for women tended to be associated with higher in‐hospital mortality.
Researchers found that women with levels higher than 14.92 g/dL had a tendency for higher in‐hospital mortality compared with the reference range of hemoglobin (OR = 2.06; 95% CI, 0.93-5.67; P = .073). For men with hemoglobin levels higher than 15.62 g/dL, the OR was 1.05 (95% CI, 0.62-1.92; P = .925).
Although not significant, researchers observed a higher incidence of in‐hospital mortality for women with a hemoglobin level lower than 13.4 g/dL (OR = 1.51; 95% CI, 0.82-2.94; P = .18); however, men with hemoglobin less than 13.25 g/dL had significantly higher mortality than the reference range (OR = 2.11; 95% CI, 1.1-4.05; P = .025).
In women, hemoglobin below the calculated reference range was correlated with higher 6‐month and 1‐year mortality (HR for both = 1.51; 95% CI, 1.09-2.09; P = .014 for both).
“This was also the case for hemoglobin levels higher than 13.6 g/dL, however, HR was only significant for 1‐year mortality,” the researchers wrote.
“Another difference was the nadir of the mortality HRs moved up to higher hemoglobin levels in men, but it decreased in women compared with in‐hospital results,” the researchers wrote. “Also, compared with in‐hospital mortality, 6‐month, and 1‐year estimated HRs in women tend to decrease in higher hemoglobin levels.”
The researchers noted that higher rates of bleeding and postoperative infection were observed in the low preoperative hemoglobin level group, which could be the main causes of longer hospital stay in this group.
“Simple one‐value cutoffs in quantitative parameters are insufficient and sometimes misleading,” the researchers wrote. “Patients at the highest end of hemoglobin levels and in lower limit normal showed a tendency toward higher in‐hospital mortality after CABG. Moreover, there is a clear gender difference in hemoglobin cutoffs and effects. This study was hypothesis‐generating and needs confirmation with a more detailed analysis in a larger sample size.”
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