CENTRIFUGATION IN GP PRACTICES - CAN IT IMPROVE DIAGNOSTIC EFFICIENCY?

Editor

Potassium (K) is one of the most frequently tested analytes in the biochemistry laboratory. Because of its critical role in both cellular and electrical function it is vital that hypo and hyperkalaemia are promptly communicated to clinicians. A delay in sample centrifugation is a common cause of pseudohyperkalaemia. The follow up of pseudohyperkalaemia consumes valuable health care resources and can result in patient care delays.

The purpose of this trial of sample centrifugation at source was to verify the positive impact on the quality of potassium results (ie the number of samples requiring follow-up) reported within the literature and measure user satisfaction

A Heraeus Labofuge 300 centrifuge fitted with an 8 swing bucket rotor was installed in the Dromore GP surgery treatment room and safety checked by the supplier. To ensure the safety of patients and staff a comprehensive training program was delivered by the laboratory Biomedical scientist.

The pilot officially started in November 2014. To minimise the chances of erroneous potassium results due to samples being mistakenly re-centrifuged, the practice placed all centrifuged samples in a special labelled bag. Potassium results for the Dromore practice during the pilot period and retrospective data from November 2013 to October 2014 were extracted from the Laboratory information system and analysed by Microsoft EXCEL. User satisfaction was accessed by a post pilot questionnaire.

The total numbers of potassium requests during the pre-implementation and implementation periods, presented in Table 1, were similar. There was a 2% increase in requests. This increase in activity is consistent with the long term activity trend for biochemistry analysis.

Table 1:

Proportion of results per concentration category

	Pre implementation		Post implementation
	Number of samples	% of total sample number	Number of samples	% of total sample number
Dashed out	434	10.68	32	0.77
<3.5	38	0.93	39	0.94
Normal range	3365	82.78	3912	94.54
>5.3-6	210	5.17	140	3.38
>6	18	0.44	15	0.36
TOTAL	4065		4138

Centrifugation at source improves the quality of Potassium result in 2 ways. Firstly, as evident in figure 1 and previously reported by Turner et al (2012) it reduces seasonal variation. Secondly as we see in table 1 it increases the proportion of results within the normal range thus reducing the need to follow up abnormal results. The proportion of results in the <3.5 mmol/L category was unaltered therefore the improvement is primarily due to a reduction in the elevated and dashed out categories. It is noteworthy that only in the post implementation period were values exceeding 7 reported. In these 2 patients previous results had been dashed out due to delayed separation.

Feedback from Dromore treatment room staff was extremely positive. The additional time spent centrifuging samples was offset by the flexibility of collecting samples at any time of the day rather than organising collections to coincide with the delivery vans. The footprint of the centrifuge did not significantly impact on the space within the treatment room and the noise level was not intrusive. General practitioners indicated a reduction in the time taken to review lab results and a reduction in the risk posed by alert fatigue. The Practice would encourage other practices to consider installing a centrifuge.

Centrifugation at source or an alternative such as phlebotomy centres must be an integrated component of the Pathology modernisation strategy.