Unfractionated heparin has remained the anticoagulant of choice for hemodialysis patients. The anticoagulation facilitates blood flow through the dialysis circuit and assures the patency of the dialysis membrane. Wide variations in the heparinization responses have been observed in patients undergoing this procedure. The purpose of this investigation was to measure circulating heparin levels in patients prior to and after hemodialysis.
This study included 119 ESRD patients undergoing maintenance hemodialysis after appropriate IRB approval and patient consent. For the 3–4 hour hemodialysis duration, a heparin loading dose of 1000 Units followed by two additional dosages of 500 Units/hour were administered. Citrated blood samples were collected prior to and immediately after the dialysis session. The blood samples were centrifuged for 15 minutes at 3000 g at 4°C and platelet poor plasma (PPP) was extracted.
Citrated plasma was frozen at −70°C and analyzed utilizing such clot based methods as Activated Partial Thromboplastin Time (APTT), Heptest and Prothrombinase Induced Clotting Time (PiCT). Circulating Anti-Xa levels were measured using a chromogenic substrate method. Thromboplastin induced thrombin generation was also measured using a fluorogenic substrate method, Thrombin Generation Assay (TGA). The Antithrombin (AT) levels in each of these patients were also measured using a functional assay. The circulating levels of heparin were determined using a calibration curve constructed from the heparin used in the dialysis unit. Results were computed for the individual tests and heparin concentrations were obtained using the assay based calibration procedures.
In the clot based assays such as APTT and Heptest, no significant differences between pre and post plasma samples were noted. The circulating levels of heparin were from 0 to 1.08 U/ml with a mean of 0.07 ± 0.11 for the APTT and a range of 0 to 1.98 for the Heptest with a mean of 0.09 ± 0.26 U/ml. In the PiCT test the range was from 14.0 to 300 seconds for the pre dialysis samples with a mean of 32.0 ± 38.2, whereas for the post samples the range was from 15.2 to 110 with a mean of 29.6 ± 14.0. For the Anti-Xa levels the % inhibition for the two groups was similar. The circulating Anti-Xa levels in the pre dialysis samples ranged from 0 to 0.77 with a mean of 0.10 ± 0.14, whereas the post level ranged from 0 to 0.51 with a mean of 0.13 ± 0.11. For the thrombin generation, the % inhibition levels ranged from 0 to 100% pre dialysis with a mean of 34.2 ± 34% and ranged 0 to 100% post dialysis with a mean of 44.5 ± 34.4%. The Antithrombin levels ranged from 28 to 130% with a mean of 86.6 ± 19.5% in the pre dialysis samples.
There was no significant difference between pre and post dialysis samples using APTT, Heptest and PiCT, whereas the Thrombin generation and Anti-Xa resulted in a statistically significant p value < 0.05 when comparing the two groups.
Wide variations in circulating heparin levels are noted in maintenance hemodialysis patients at pre dialysis and post dialysis time periods. Some patients exhibit higher levels of heparin due to a vascular access flush. These results also suggest that the use of heparin in maintenance hemodialysis patients in repeated regimen results in a steady state hypocoagulation as evidenced by the inhibition of thrombin generation, circulating Anti-Xa level and the prolongation of various clotting times.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.