3a Emergency and massive transfusion

Photo-Optical Methods Can Lead to Clinically Relevant Overestimation of Fibrinogen Concentration in Plasma Diluted With Hydroxyethyl Starch

Background: Adequate fibrinogen concentration is a crucial component of sufficient perioperative/posttraumatic hemostasis. In major blood loss, large volumes of fluids are being administered, which have been shown to interfere with valid determination of fibrinogen concentration. This may lead to wrong treatment decisions. We studied the variables that cause the discrepancies between measured and true fibrinogen concentrations in samples diluted with volume replacement fluids. Methods: Citrated plasma samples of healthy volunteers were diluted by 30% and 50% with phosphate buffered saline (PBS), hydroxyethyl starch (HES) 10% (200/0.5), or gelatine (GEL). Fibrinogen concentrations of diluted samples were derived from the prothrombin time (PT) and the Clauss method (CLS) was applied. With the latter, several modifications and combinations of detection principles and thrombin reagents were investigated. Values were compared with ‘‘true,’’ that is, calculated values based on the results of undiluted samples for each method. Results: Photo-optical methods resulted in significant overestimation of the fibrinogen concentration in blood diluted with HES, depending on the thrombin reagent used. This was particularly true for modifications of the CLS aimed at measuring low fibrinogen concentrations. Use of another thrombin reagent gave satisfactory results for this modification. The validity of mechanical end point determination methods was considered sufficient and was not influenced by the use of different thrombin reagents. Conclusions: Fibrinogen determination methods used in situations of major blood loss need to be validated with samples containing significant amounts of volume replacement fluids, particularly colloids. Only some combinations of test principle, detection method, and reagents will give valid results.

Influence of different hydroxyethyl starch (HES) formulations on fibrinogen measurement in HES-diluted plasma

BACKGROUND

Fibrinogen is the first coagulation factor becoming critical in dilution coagulopathy. Volume replacement in major blood loss is performed with large volumes of crystalloid and colloid solutions. The latter has been shown to compromise accurate photo-optical measurement of fibrinogen. This study determined the influence of different hydroxyethyl starch (HES) formulations.

METHODS

Citrated plasma samples of 8 healthy volunteers were diluted by 30% or 50% with either HES 10% (200/0.5; HES-200), HES 6% (70/0.5; HES-70), or HES 6% (450/0.7; HES-450). Fibrinogen concentrations were determined by photo-optical measurement (Behring coagulation system [BCS]: derived fibrinogen, or Clauss fibrinogen, calibrated for high [CLS] or low fibrinogen concentrations [CLS-low]) as well as mechanical end point determinations (KC4: CLS-KC4). Measured values were compared with calculated values.

RESULTS

On average and across all photo-optical methods, fibrinogen concentrations were overestimated, particularly with HES-200. Hydroxyethyl starch-70 and HES-450 did not differ much from each other. Overestimation was relatively greater for 50% dilutions with all HES formulations. Surprisingly, overestimation was most prominent with CLS-low, the method supposed to most reliably measure low fibrinogen concentrations; overestimation amounted to 92% and 120% with HES-200, 54% and 73% with HES-70, and 51% and 79% with HES-450, for 30% and 50% dilutions, respectively. In contrast, CLS-KC4 always yielded sufficiently accurate results.

CONCLUSIONS

The study showed that all HES solutions more or less impaired the fibrinogen measurement with the photo-optical method. In particular, overestimation with CLS-low may prevent timely fibrinogen replacement in major blood loss. Hydroxyethyl starch concentration appears to be more relevant for this effect than its molecular size.