Routine Blood Sampling and Hidden Blood Loss in ICU Patients.

BACKGROUND: Anaemia is common in critically ill patients and is associated with adverse outcomes. Diagnostic blood sampling is a potentially modifiable contributor to iatrogenic blood loss, yet its cumulative impact is often underestimated. AIM: To evaluate the impact of routine diagnostic blood sampling on haemoglobin decline, anaemia at ICU discharge and transfusion requirements. STUDY DESIGN: This is a retrospective cohort study of adult ICU patients in a tertiary care teaching hospital in India. Haemoglobin levels at admission and discharge, total diagnostic blood loss and transfusion requirements were recorded. Associations between variables were assessed using correlation analysis and multivariable logistic regression. RESULTS: Among the 109 patients included in the study, haemoglobin decreased significantly during ICU stay from 13.1 g/dL on admission to 10.8 g/dL at discharge (mean difference -2.38 g/dL, 95% CI -2.65 to -2.10, p < 0.001). Over half of patients developed anaemia by discharge. Admission haemoglobin was the strongest independent predictor of anaemia (p < 0.001). Total blood volume lost showed a moderate correlation with haemoglobin decline (r = 0.56). ICU length of stay was strongly associated with cumulative blood loss (r = 0.92) and moderately with haemoglobin decline (r = 0.57). Approximately half of patients required red blood cell transfusion. CONCLUSIONS: Routine diagnostic blood sampling contributes to haemoglobin decline in ICU patients, with cumulative blood loss increasing over time. Patients with lower baseline haemoglobin are particularly vulnerable to developing anaemia. Reducing unnecessary sampling and discard volumes represents a simple, low-cost, nursing-led blood conservation strategy that can support patient blood management and reduce avoidable transfusion exposure in critical care settings. RELEVANCE TO CLINICAL PRACTICE: Blood sampling practices represent a modifiable source of iatrogenic harm. Strategies such as minimising unnecessary tests, reducing discard volumes and identifying high-risk patients may help reduce anaemia and transfusion requirements in critical care settings.