Discharge Hemoglobin < 8 g/dL is Associated with Increased 30-day Readmission Rates after CABG

From the 2018 HVPAA National Conference

Vincent DeMario (Johns Hopkins School of Medicine), Brian Cho (Johns Hopkins School of Medicine), Glenn Whitman (Johns Hopkins School of Medicine), Michael Grant (Johns Hopkins School of Medicine), Nadia Hensley (Johns Hopkins School of Medicine), Charles Brown, IV (Johns Hopkins School of Medicine), Sachidanand Hebbar (Johns Hopkins School of Medicine), Kaushik Mandal (Johns Hopkins School of Medicine), Steven Frank (Johns Hopkins School of Medicine)

Background

High-value care is promoted by a restrictive transfusion strategy in cardiac surgery, resulting in decreased blood utilization with similar outcomes, compared to a liberal transfusion strategy. What remains to be determined, however is the impact of lower discharge hemoglobin (Hb) levels on readmission rates.

Objectives

We assessed patients with higher versus lower Hb levels upon discharge to compare 30-day readmission rates after coronary artery bypass grafting (CABG).

Methods

We retrospectively evaluated 1,552 patients undergoing isolated CABG at our institution from Jan 2013 to May 2016. We evaluated two Hb cohorts: “High” (above) and “Low” (below) the mean discharge Hb level of 9.4 g/dL, comparing patient characteristics, blood utilization, and clinical outcomes including 30-day readmission rates. We further evaluated the effects of the lowest (< 8 g/dL) discharge Hb levels on 30-day readmission rates. Risk adjustment accounted for age, gender, Charlson comorbidity index, preoperative comorbidities, and patient blood management program implementation.

Results

On multivariable analysis, the risk-adjusted odds of readmission in the “Low” Hb cohort (OR 1.17; 95% CI 0.85 to 1.62) (P = 0.34) was not significant compared to the “High” Hb cohort. However, a Hb < 8 g/dL upon discharge was predictive of readmission (OR 1.69; 95% CI 1.01 – 2.78) (P = 0.047) and there was a trend for increased risk of 30-day readmission rates with every 1 g/dL decrease in discharge Hb (Table 1). A LOWESS curve shows an increase in 30-day readmission rates when discharge Hb levels are < 8 g/dL and a plateau in the 30-day readmission rate between 8 g/dL and 12.5 g/dL (Figure 1).

Conclusion

A discharge Hb level below the institution mean for CABG patients is not associated with an increased 30-day readmission rate, however, in the small number of patients discharged with Hb < 8 g/dL, there is a suggestion of increased risk for readmission. High-value care includes reducing unnecessary transfusions, although the relationship between anemia and readmissions after cardiac surgery needs to be assessed by prospective controlled trials to support or refute our findings.

Implications for the Patient

In this retrospective study, the small number of cardiac surgery patients with a hemoglobin < 8 g/dL upon discharge had an increased rate of 30-day readmissions. Reducing unnecessary transfusions promotes high-value practice, however caution is warranted regarding the readmission risks with anemia.

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