PORTABLE BLOOD GLUCOSE MONITORS (PBGMs): A BITTERSWEET TOOL IN DAILY PRACTICE
PBGMs are human point-of-care instruments used in veterinary practice to monitor blood glucose and to provide an indication of hyper or hypoglycaemia, which can both be critical medical conditions.
They are very useful tools but there are few caveats you need to be aware of, to avoid serious clinical mistakes.
- The importance of FASTED SAMPLE: hypertriglyceridemia results into pseudo hypoglycaemia. Therefore, a fasting period must exceed 8 hours for an accurate glucose measurement.
- Hyperbilirubinemia can lead to glucose results being increased by up to 21%.
- Acidosis falsely decreases glucose concentration. Therefore, be careful when monitoring ketoacidotic patients.
- Drugs/treatment can also cause interferences; therefore, it is always recommended to follow manufacturer instructions.
HOW PBGMS WORK
- The glucose distribution is different depending on the species. In people, glucose is equally distributed between plasma and erythrocytes (50% in RBC and 50% in plasma), whereas the glucose contained in canine and feline erythrocytes is much lower (12.5% in RBC + 87.5% in plasma and 7% in RBC + 93% in plasma, respectively). For this reason, it is recommended to use only PBGM validated for the animal species you need to monitor. PBGMs marketed for veterinary species contains algorithms to account for specific RBC glucose binding capacity and recent publications established that they provide reliable results.
- Glucose results from whole blood or serum/plasma are NOT INTERCHANGEABLE. The amount of glucose in whole blood (plasma + RBC) is less than in an equivalent volume of plasma or serum, therefore low HCT leads to falsely higher glucose levels. It is important to find out what your PBGM measures and reports.
- PBGMs operates with different technologies (i.e. optical method, electromechanical method) and the current literature reports high result variability amongst different PBGMs. For this reason, it is important to monitor glucose level ALWAYS with the SAME INSTRUMENT.
- Because of these inconsistencies among PBGMs, blood glucose concentrations obtained with any newly purchased PBGM should be compared with values obtained with a reference method to determine whether the glucometer tends to provide values that are low, high, or both. This procedure is called PROFICIENCY TESTING.
- Serum or plasma samples from patients with hypo, normal and hyperglycaemia must be split and analyses the same day with the meter and at the referring laboratory. Specifically, plasma should be separated within 5 minutes of collection, and serum should be separated from the clot within 2 hours in dogs and cats.
- Make sure to follow manufacturer recommendations regarding strips expiry date, entering key code, use of provided control materials and storage.
MINIMIZING POST ANALYTIC ERRORS
- Units of measurements must be consistent to avoid misinterpretation of results. Conversion factor: Glucose mmol/L x 18.018 = mg/dL Glucose mg/dL x 0.0555 = mmol/L
Any animal identified by a PBGM as being hypoglycaemic should be retested with a reference analyser before diagnostic testing to identify an underlying cause is initiated. This is recommended because it is reported that human PBGMs tend to underestimate glucose levels in dogs and cats.
In summary, it is prudent to minimize the number of variables when performing serial glucose tests in one animal by consistently using identical blood sampling technique and the same glucometer.
BattLab can assist you in performing and interpreting a proficiency testing of your PBGM. Please contact us if you are interested in this service.