Utility of Repeating a Hemoglobin Level to Detect a Drop in a Single Day

Background:

Clinicians check complete blood counts (CBC) multiple times over a hospitalization and sometimes multiple times in a single day, often with the goal of detecting a drop in the hemoglobin level. However, phlebotomy is associated with risks, including hospital‐acquired anemia, patient discomfort, and increased costs. The objective of our study was to determine on days when a hemoglobin was checked twice, how often the second result was significantly lower than the first.

Methods:

We identified all hemoglobin test results obtained from adult inpatients hospitalized for at least 24 hours at UCSF Medical Center who were discharged between September 1, 2012 to September 1, 2013. We restricted the analysis to patients who had 2 hemoglobins obtained during a calendar day because patients with ≥ 3 tests within a day were likely to have a strong indication for repeat testing. We used descriptive statistics and t‐tests to analyze mean changes of hemoglobin values.

Results:

There were 17,042 unique patients hospitalized during 100,458 days where at least one hemoglobin value was obtained: 83,550 (83%) days with a single hemoglobin result, 11,182 (11%) with two, and 5,726 (6%) with ≥ 3 results. Of the 11,182 days with twice daily checks, the mean value of the first hemoglobin obtained was 10.1 ± 2.1 g/dL and the mean value of the second hemoglobin was 10.2 ± 1.8 g/dL, with a mean change from the first to second of 0.05 g/dl (95% Confidence Interval (CI) 0.04‐0.08). Eighty‐six percent of repeat hemoglobin tests obtained within the same day were within 1 g/dL of the first value and 3% were ≥2 g/dL lower. Only 8.3% of repeat hemoglobin results were < 8 g/dL and 1.5% were <7 g/dL. Among patients whose initial hemoglobin was less than 10 g/dL, only 3.6% of repeated tests declined ≥1 g/dL and 2.8% of repeats were <7 g/dL. When patient days associated with a transfusion or a bleeding diagnosis were excluded, 2.9% of those patients had ≥1 g/dL decline and 1.7% of repeat tests were <7g/dL. By comparison, on patient‐days with the same exclusion criteria but with an initial hemoglobin value greater than or equal to 10 g/dL, 17.8% had a ≥1 g/dL decline and 0.1% of repeat tests were < 7g/dL.

Conclusions:

Among anemic patients who are not given a transfusion or a bleeding diagnosis, fewer than 3% had a hemoglobin drop of more than 1 g/dL within the same day. Clinicians should carefully consider the utility of repeating a same‐day hemoglobin.