Predictive Model: Blood Glucose Concentrations

Blood samples from 6 healthy and 30 hospitalized dogs were examined to determine the effect of packed cell volume (PCV) on point-of-care glucometer (POCgluc) measurements in canine blood samples. Packed RBC samples from the healthy dogs were suspended with plasma to create PCVs ranging from 0% to 94%. POCgluc and PCV measurements from dilution and plasma cells were then analyzed for glucose concentration with a clinical laboratory biochemical analyzer (LABgluc). 

Blood glucose values from LABgluc were similar at all dilutions. However, as PCV decreased, POCgluc measurements were falsely increased; as PCV increased, POCgluc measurements were falsely decreased. This inaccuracy is believed to correlate with the degree of plasma displacement by erythrocytes. Increased erythrocyte volume in whole blood decreases the volume of plasma available for contact with reagents on glucose test strips in POCglucs. The absolute difference between POCgluc and LABgluc results increased as the PCV changed from 50%. POCgluc measurements for PCVs between 42% and 56% generally had ≤10 mg/dL deviation from LABgluc measurements. 

A formula was developed to correct the POCgluc given a known PCV to predict patient glucose concentrations: 

Corrected POCgluc = POCgluc + ([1.6 × PCV] – 81.3)

Using this formula reduced the error resulting from hemodilution or hemoconcentration. Corrected POCgluc data had significant correlations with LABgluc data in hospitalized dogs. Ideally, a point-of-care device would measure both hematocrit and glucose concentrations and use an internal correction formula before display.

Commentary

Changes in PCV outside of the reference range can result in falsely increased or decreased blood glucose measurements when POCglucs are used. Corrective formulas can be derived but would be specific to individual glucometers. It is also important to recognize that corrective formulas are often less accurate at extremes of hyper- or hypoglycemia.—Kirsten Cooke, DVM, DACVIM