Multicomponent assay for blood substrates in human sera and haemolysed blood by mid-infrared spectroscopy

A method of multicomponent analysis for blood substrates (glucose, total protein, total cholesterol, triglycerides, haemoglobin, and urea) based on FT-IR spectroscopy is described. Venous and capillary blood was used as a matrix, with sample volumes as small as 1 mu l. The spectra were obtained by transmission and diffuse reflection measurements from dried samples on a disposable carrier. The mean square prediction errors for 90 blood samples from different patients, calculated by cross-validation, were found to be 18 mg/dl for glucose, 17.5 mg/dl for cholesterol, 23.5 mg/dl for triglycerides, and 0.77 g/dl for haemoglobin. The mean square prediction errors for serum analyses are smaller: for a population of more than 200 serum samples we found 8 mg/dl for glucose, 12 mg/dl for cholesterol, 14.9 mg/dl for triglycerides, 0.23 g/dl for total proteins, and 8.7 mg/dl for urea. The in-series standard error for the glucose concentration (human sera) was low as 2.2 mg/dl (n = 20). The combined spectroscopic and biological error for glucose was found to be 7 mg/dl. This value includes the "matrix effect". In independent serum samples glucose concentrations were measured with a total error of 16 mg/dl.