Heparin Infusion for Central Line Patency and Corrected Gestational Age May Affect Coagulation Studies in the Neonatal Intensive Care Unit

Introduction: Addition of heparin (i.e., 0.5-1 U/mL) to maintenance intravenous (IV) fluids in the neonatal intensive care unit (NICU) is frequently done to reduce the risk of thrombus-related catheter dysfunction. Since heparin could affect coagulation testing, we sought to determine whether coagulation study results are significantly affected by the presence of heparin in IV fluids.

Methods: Chart review was performed on all patients in the NICU that had either prothrombin time (PT) or partial thromboplastin time (aPTT) drawn during their NICU course. Only the first instance of coagulation studies drawn on each patient was considered. Patients were excluded if they had a medical condition (e.g., sepsis) which could potentially affect coagulation studies or if they received blood products. Coagulation study results and whether or not the patient was receiving heparin in IV fluids for vascular access patency were extracted in addition to other demographic information, including corrected gestational age (CGA). In our institution, all NICU patients with a central line where the flow rate in any lumen is less than 5 mL/hr receive heparin. Comparative analyses between the group receiving heparin in IV fluids and the group not receiving heparin were performed. Wilcoxon rank sum test was used to detect differences in distribution between groups and adjustment was performed by fitting one multiple linear regression model to medians and a separate multiple linear regression model to standard deviations; Z-scores were calculated based off these two models.

Results: One hundred and forty four patients (mean age 17.9 days, 50% male) were included in the analysis. Initial unadjusted analysis revealed that patients who received heparin in IV fluids for vascular access patency (n=77, 53.5%) had prolongation of PT and aPTT compared to patients who did not receive heparin (n=67, 46.5%) in IV fluids for vascular access patency (means 16.2 seconds vs. 13.5 seconds [p=8 x 10^-7] and 62.9 vs. 43.9 seconds [p=9 x 10^-8], for PT and aPTT, respectively). No significant sex-based difference was noted.In 132 patients with accurate CGA data available, mean CGA was lower in the heparin group (n=75) at 36.5 weeks compared to the no heparin group (n=57) at 41.6 weeks (p<0.0001). When results were adjusted for CGA, the difference remained significant but much less so (z-score mean difference 0.52 [p=0.01] and 0.48 [p=0.003], for PT and aPTT, respectively).

Conclusion: Coagulation study parameters appear to be prolonged in patients receiving heparin for vascular access patency compared to those who are not; however, much of this difference is accounted for by corrected gestational age. Proper specimen collection (i.e., sufficient draw-back prior to collecting the sample) for accurate interpretation of results in these patients is recommended. In addition, laboratories should consider taking corrected gestational age and continuous low-dose heparin infusion into account when establishing reference ranges for coagulation studies.