Issue: We have received a number of calls consistent with the following scenario: Patient is
drawn in early AM. CBC performed and reports a “critical value” on Hemoglobin and/or
Hematocrit. Patient admitted to hospital for possible transfusion. Hospital draws CBC for
evaluation and finds the Hgb/Hct is now higher and not critical and the patient does not require
a transfusion or receives an unnecessary transfusion.
Review: On each one of these calls, Doctors Lab has reviewed each case to insure that there
were no instrument or system failures. We have reviewed: Correct patient drawn, Instrument
maintenance and QC. We sent split samples to other labs and have re-drawn patients and sent
split samples to other labs for comparison. We contacted the instrument manufacturer. None
of these review processes have satisfactorily identified an “issue” that could or should be
corrected. After each review we felt confident in the accuracy of the results that we provided.
However, we still had no satisfactory explanation for the lower results that we reported.
Note: we were anxious to resolve this issue as the “tendency” is to assume that the laboratory
and its results are always the ones who are wrong.
Conclusion: After our case reviews, we continued to research possible explanations for the
phenomenon that we and you were experiencing. As we have searched the literature, we
believe that we have found a plausible explanation to accurately explain the differences in the
- Our results confirm the theory that a change in posture causes changes in some of the blood indices; posture changes the hydrostatic pressure that leads to a change in the movement of fluid between interstitial space and intravascular space and causes physiologic fluctuations in blood volume.
- It is recommended that healthcare providers consider the postural pseudo-anemia phenomena in the event of a Critical Hgb or Hct prior to admitting for possible transfusion.
- Changes in posture can lead to substantial changes in Hgb/Hct, which may be attributed mistakenly to blood loss or acute anemia and result in a cascade of unnecessary diagnostic costs. In reality, these changes represent postural pseudoanemia, a normal p hysiological response to a change in position from standing to lying (and vice versa).
From our literature reviews and our own in-house study, we believe that the Postural Pseudoanemia phenomena is most likely the reason for most of the differing CBC results between the
early AM and later in the day draws.
Recommendations: We believe that this Postural Pseudo-anemia phenomena is probably
happening on most of our patient results but does not become an “issue” until the results
approach the Critical Values borders.
Our recommendation: Change the position of the patient and call us for a STAT redraw prior to
Summary: When receiving a Critical Value on a Hgb/Hct on an early AM draw that could
potentially indicate the need for a transfusion (especially in the absence of other clinical
indications of bleeding or anemia), is to get the patient up (change of posture) and redraw the
sample before admitting to the hospital. Call us for STAT redraw.