We read with interest the article by Karkouti et al.1  published in the March 2015 issue regarding a transfusion algorithm based on point-of-care coagulation tests in cardiac surgery.

We wish to shed light on an issue that was not touched upon in the article but represents the first step in their algorithm and, without dispute, the first and most important single intervention in managing postcardiopulmonary bypass coagulopathy.

The dose of the heparin neutralization by protamine is shown in the algorithm as a ratio of milligrams to milligram. It has long been recommended that heparin should not be quantified in milligram, but in units.2–4  In fact, to our knowledge, none of the currently available commercial heparins display its potency in milligram. This quantification of heparin in milligram introduces risk if the ordering physician is unfamiliar with the milligram to unit conversion.

The impression that 1 mg unfractionated heparin currently contains 100 units is widely accepted but dated and erroneous. One milligram heparin has contained 130 units of heparin at least since the Second International Standardization in 1968.2,5  More recently, after contamination issues, the Food and Drug Administration and U.S. Pharmacopeia have mandated a new reference standard for heparin, and 1 mg heparin now contains not less than 180 units.6,7  We do not think this change in heparin formulation is recognized widely and hence advocating heparin use in milligram may lead to a variable interpretation and dosing.

Furthermore, the Society of Thoracic Surgeons and Society of Cardiac Anesthesiologists Practice Guidelines for Blood Transfusion and Conservation in Cardiac Surgery (2007, updated in 2011)8,9  have recommend using either a low-dose protamine protocol (50% of heparin dose) or a titrated protamine dose guided by activated clotting time response testing to neutralize heparinization in the postcardiopulmonary bypass patient. Although the evidence in favor is not strong, we wonder if adherence to above guidelines may have impacted the data presented.

Advances in technology such as point-of-care coagulation testing should be embraced in a timely manner, but we must acknowledge that age-old drugs such as heparin and protamine have not yet been evaluated systematically in cardiac surgery.

The authors declare no competing interests.

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