ObjectivesWe sought to investigate if duplicate faecal immunochemical testing (FIT) sampling improves the negative and positive predictive value of patients thought to be at risk of colorectal cancer (CRC). Specifically, we aimed to investigate whether the proportion of FIT-negative CRC missed by a single FIT test in symptomatic patients could be reduced by duplicate FIT testing.DesignA retrospective service evaluation cohort study of the diagnostic accuracy of duplicate FIT testing.SettingPatients referred from primary care with suspected CRC to four secondary care trusts in North-West England.Participants28 622 patients over 18-years-old with lower gastrointestinal symptoms suggestive of CRC who completed two FIT samples.Primary and secondary outcome measuresThe performance of duplicate FIT for detecting CRC at a threshold of 10 µgHb/g.ResultsThe sensitivity if either test was >10 µgHb/g was 0.978 (0.955–0.989), specificity was 0.662 (0.657–0.668), positive predictive value 0.031 (0.028–0.035) and negative predictive value 1.00 (0.999–1.00). Despite two-thirds of patients (18952) being negative following two tests, at this threshold only seven CRC were missed over a 26-month period. All seven patients had other high-risk features which should have prompted investigation.ConclusionsThis study suggests that in routine NHS practice, a duplicate FIT sample strategy together with clinical evaluation for evidence of anaemia and weight loss is superior to a single FIT sample alone and would allow symptomatic patients to be managed in primary care without the need for urgent referral to secondary care for urgent colonic imaging.

Use of point-of-care blood ketone testing to diagnose and monitor patients with diabetic ketoacidosisIn a recent editorial, Dhatariya 1 discussed the use of point-of-care blood ketone monitors in the management of diabetic ketoacidosis (DKA) in adults. Following the publication of the Joint British Diabetes Society guidelines on the management of DKA in adults, 2 we introduced blood ketone testing at the bedside using Abbott Precision Xceed Pro meters.Where possible, it is advisable that point-of-care testing (POCT) should be supported by a laboratory method for the same analyte, so that results outside the measurable range of the device, or results which are not consistent with the clinical picture, may be verified or otherwise. We, therefore, evaluated and introduced a laboratory method for betahydroxybutyrate (BHB). Like others, we found good agreement between results of POCT capillary ketone measurement using bedside meters, and laboratory BHB results obtained on venous serum samples, up to a concentration of 3 mmol/L.3,4 Above 3 mmol/L, POCT results were consistently lower than serum BHB measured on venous samples. For example, one patient had a capillary POCT ketone result of 5.4 mmol/L but a laboratory venous serum BHB of 13.7 mmol/L. Dhatariya is correct to point out that both results give a diagnosis of DKA and that the rate of decline is rarely if ever used in isolation to guide treatment. However, we think it is important that all users of POCT ketone meters are aware of this limitation. In our comparison study, some patients appeared to show no or very little response to treatment using capillary POCT ketone tests, whereas laboratory measurements on venous samples showed an appropriate decrease in BHB (>0.5 mmol/L/h).2 For example, one patient had a capillary POCT ketone result of 3.6 mmol/L initially, which decreased to 3.3 mmol/L after 5 h of treatment. By contrast, BHB laboratory results on venous samples collected simultaneously showed a fall from 12.7 mmol/L to 3.1 mmol/L. Capillary POCT ketone measurement alone may give a false impression that ketoacidosis is not resolving.We also measured venous blood ketones using the same POCT meters and found good agreement with venous blood BHB measurements, suggesting that the falsely low results observed using capillary samples reflect the characteristics of capillary blood rather than the meter itself. Therefore, this limitation may potentially affect all POCT meters using capillary samples to measure ketones.We have introduced routine laboratory BHB analysis and incorporated venous BHB measurement into our local DKA guideline. We have also included a statement in our guideline to ensure that blood ketone monitoring is never used on its own to guide treatment:When blood ketones are >3.0 mmol/L, ketone meter measurements using capillary blood may underestimate the actual value and rate of change may also be falsely low. Review venous ketone results and also assess change in capillary glucose and venous bicarbonate to help determine if IV insulin rate nee...

Limitations to using point of care blood ketone testing to monitor DKA treatmentSir, After recommendations from the Joint British Diabetes Societies to use bedside monitoring of blood ketones in the management of diabetic ketoacidosis (DKA), 1 a number of UK hospitals have introduced point of care testing (POCT) for measurement of blood ketones. The guidelines state that the method of choice for monitoring the response to treatment is bedside measurement of capillary blood ketones. Many of the devices used in hospitals to measure blood glucose at the patient's bedside are also able to measure ketones; specifically, betahydroxybutyrate (BHB) which is the predominant ketone present in DKA. The guidelines also recommend that one of the main therapeutic targets should be a reduction in blood ketones by 0.5mmol/L per hour. If this target is not reached, it is recommended that the insulin infusion rate should be increased.We introduced bedside blood ketone testing using the Abbott Precision Xceed Pro meter with Precision Xceed Pro β ketone test strips. We decided to evaluate and introduce a laboratory method for BHB as it is advisable that for all POCT there should be a laboratory method available if the result is outside the measurable range of the device, if the result does not fit clinically or if there are contraindications to using the POCT device in particular patients. As part of the evaluation, we compared a laboratory BHB method (Randox RanBut D-3 hydroxybutyrate reagents on the Roche P Module) to the POCT capillary blood ketone results. Venous serum samples collected within 1 hour of the POCT capillary blood ketone test were analysed using the laboratory BHB method. Additionally, we compared the results obtained using the laboratory and POCT method on the same venous sample (Figure 1).There was good agreement between the POCT capillary blood ketone results and laboratory venous serum BHB results up to a BHB concentration of 3mmol/L. Above 3mmol/L, the POCT capillary blood ketone results were consistently lower than the laboratory venous serum results. Janssen et al. also advise caution on results above 3mmol/L. 2 However, when the venous samples were tested using the Abbott meter, there was very good correlation between the laboratory results and the POCT results. Therefore, the lower results observed in the capillary whole blood samples are most likely to be a problem with the capillary sample rather than the POCT ketone test itself. We hypothesise that dehydration and decreased peripheral circulation, often seen in DKA patients, are factors affecting the quality of the capillary blood sample and the ketone concentration above 3mmol/L. These findings have implications when trying to use POCT capillary blood ketone tests to monitor patients with DKA. Using the target reduction of 0.5mmol/L per hour will be acceptable if the ketone concentration is <3mmol/L. However, due to the underestimation of POCT ketones using capillary samples, a reduction in ketones may not be demonstrated using the meter if the ketone ...