It would be advantageous to be able to measure glycosylated hemoglobin (GHb) from a sample of blood dried on paper and sent to the physician by the patient. Indeed, such a technique has been introduced by Isolab (Akron, OH). We tested the validity of the method to determine whether 1) applying the blood to paper and immediately assaying it correlates with the same sample assayed by the usual wholeblood technique, 2) the size of sample applied to paper affects apparent GHb results, 3) time and temperature of storage of the sample paper affect apparent GHb resu ts, and 4) plasma glucose concentration of the sample affects GHb results.
The GHb of samples assayed immediately after application to sample paper versus those assayed as whole blood showed very good correlation (r = .93, P < .001). Volume of the drop of blood applied to paper (25–100 μl) did not affect results. However, there was a dramatic, temperature-dependent increase in apparent GHb when samples were stored on sample paper, averaging 12.5, 16.3, and 19.5% when stored at room temperature for 3, 6, and 9 days, respectively. Overall, apparent GHb rose from 1.3-fold in 3 days at 4°C to 3.8-fold in 9 days at 37°C. The rate of GHb formation was proportional to plasma glucose concentration, but removal of free glucose by ethanol or glucose oxidase did not yield consistent results for this method. We conclude that these sample papers are not useful as an approach to collecting blood samples for GHb measurement.