BEWARE THE LOCK! A CASE OF PSUEDOHYPERNATRAEMIA IN A HAEMODIALYSIS PATIENT

J WONG1, J  DIEP1, L WIEDERSEHN1, A CILLEKENS2, F ALVARO3

1Renal Unit Liverpool Hospital, Sydney, Australia, 2Department of Haematology Liverpool Hospital, Sydney, Australia, 3Dept Clinical Chemistry Liverpool Hospital, Sydney, Australia

Case: A 1030 PM call was received from the laboratory re publishing sodium 185 mmol/L from a haemodialysis patient tested in preparation for general anaesthesia the next day. The patient had departed with printed copies of results minus the sodium. The laboratory had rechecked the sample including on a second analyser. Phone discussions with haemodialysis staff and patient indicated nothing outstanding. The patient, a 47 year old female, dialysing via a tunneled catheter(TC) for 14 months  was well and refused repeat testing prior to her morning operation in another institution.
Hypothesis: Suspected contamination by Trisodium Citrate 46.7% catheter lock – [Sodium] is 4903.5mmol/L. Departmental TC blood sampling algorithm was complex: A. 3ml lock discarded, B. 20 mls withdrawn (to be returned after C.) C. Sample(s) taken.
Investigation: Repeat samples A-C above and D. after 5 mins on haemodialysis, and E. reference peripheral blood sample on the same patient, another TC patient with Citrate Lock and 2 patients whose TCs were locked with heparin 5000u/ml were analysed.
Results: Citrate TCs: Sample A showed ave. [sodium] of 1522 mmol/L, [K] of 10 mmol/L, Osmol 1963 and grossly abnormal reductions in [Cl],[HCO3],[urea],[creatinine],[Ca],[Mg],[PO4], [albumin],Hb and PCV compared with all other sample points (B,C,D &E) which were within 5% of each other. For heparin locked TCs: Sample A showed ave. [Sodium] 117 mmol/L, [K] 4.5 mmol/L, Osmol 207 and grossly abnormal reductions in other tested indices compared with all other sample points which were within 5% of each other.
Conclusions: Grossly abnormal laboratory results can arise from TC lock blood sample contamination. We could not identify the exact error in blood sampling however our complex sampling method needs


Biography:
Dr Jeff Wong has been a staff specialist nephrologist at the South Western Sydney Local Health District since 2004. He obtained his medical degree through Otago University in Dunedin New Zealand. Dr Wong’s advanced training commenced in Wellington, New Zealand and was completed in Sydney, followed by a basic science PhD through University of Sydney and the transplant unit at Westmead hospital on Chemokines in Cellular Xenograft Rejection.

Dr Wong’s main interests and roles at Liverpool hospital have been in peritoneal dialysis and the development of an interventional nephrology unit, where he manages the imaged guided catheter based access (Tunneled lines and PD catheters) for their large dialysis population of approx.700. This led to a role in the development of the ANZSIN in 2008 which has now regularly held with the ANZSN. Dr Wong has a keen interest in medical education and supervision of students and trainees

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