The case of the floating gel: Figure 1

Abstract

In patients with chronic renal failure, blood samples for laboratory analysis are often taken via dialysis catheters. This report describes a case of gross spurious hypernatraemia in a blood sample collected from a patient undergoing haemodialysis. After centrifugation of the blood sample in question, the separator gel formed the topmost layer, with the serum in the middle and the clot at the bottom. Subsequent analysis of the serum showed severe hypernatraemia (serum sodium, 744 mmol/litre). It was established that the blood sample had been taken from the patient’s dialysis catheter into which 3 ml of Citra-Lock™ (46.7% trisodium citrate) had been instilled previously as a “catheter locking” solution. The hypernatraemia seen in this case was recognised immediately as an artefact, but it was found that even minimal contamination of blood samples with Citra-Lock may significantly affect sodium concentrations. This contamination may be missed, with potentially adverse consequences for patient management.

Thyrotoxicosis factitia: author's response

“…The higher osmolality with Citra-lock TM contaminated samples is likely to be related to the high concentration of sodium citrate present in Citra-lock TM such that there is very little dilution of the original sample. According to the article by Srivastava and Murphy et al 2 only 10 mL of Citra-lock TM is sufficient to increase the serum sodium concentration by approximately 20 mmol/L. …”

An Unusual Case of a Primary Blood Collection Tube with Floating Separator Gel

“…The aspiration of gel along with the sample matrix might also spuriously modify the test results, since an inappropriate amount of serum or plasma would be analyzed. The causes which have been anecdotally implicated in an inappropriate gel barrier formation include the administration of radio contrast dye , as well as the presence of hyperproteinemia or trisodium citrate solution in the specimen. In these circumstances, the specific gravity of serum or plasma is considerably high, thus preventing the appropriate positioning of the gel in the primary tube, since the migration of the gel during centrifugation of the tube is mainly determined by the density rather than the viscosity of the sample matrix .…”

Anomalous Flotation of Separator Gel: Density or Viscosity?

“…Although the number of reported cases seems low, the impact on cost and the risk of reporting misleading values is substantial (1 ). Different interpretations have been proposed regarding whether the anomalous flotation of the gel is a matter of density or viscosity of the serum/plasma (2)(3)(4). We investigated whether this gel behavior was due to the high density or to the high viscosity of the liquid phase in a case of floating separator gel in samples from a 70-year-old woman in whom IgA myeloma was subsequently diagnosed.…”