Patterned Paper as a Platform for Inexpensive, Low-Volume, Portable Bioassays

The developing world does not have access to many of the best medical diagnostic technologies; they were designed for air-conditioned laboratories, refrigerated storage of chemicals, a constant supply of calibrators and reagents, stable electrical power, highly trained personnel and rapid transportation of samples. Microfluidic systems allow miniaturization and integration of complex functions, which could move sophisticated diagnostic tools out of the developed-world laboratory. These systems must be inexpensive, but also accurate, reliable, rugged and well suited to the medical and social contexts of the developing world.

We studied whether microalbuminuria (30 to 140 micrograms of albumin per milliliter) would predict the later development of increased proteinuria and early mortality in Type II diabetics. During 1973, morning urine specimens of diabetic clinic patients 50 to 75 years of age whose disease had been diagnosed the age of 45 were examined for albumin level by radioimmunoassay. Seventy-six patients with albumin concentrations of 30 to 140 micrograms per milliliter were identified for long-term follow-up. They were compared with normal controls, diabetic patients with lower albumin concentrations (75 patients with concentrations less than 15 micrograms per milliliter and 53 with concentrations of 16 to 29 micrograms per milliliter), and 28 diabetic patients with higher concentrations (greater than 140). Age, duration of diabetes, treatment method, fasting blood glucose level, blood pressure, height, and weight were determined for the four diabetic groups. After nine years the group with albumin concentrations of 30 to 140 micrograms per milliliter was more likely to have clinically detectable proteinuria (greater than 400 micrograms per milliliter) than were the groups with lower concentrations. Mortality was 148 per cent higher in this group than in normal controls--comparable to the increase (116 per cent) in the group with heavy proteinuria (albumin levels greater than 140 micrograms per milliliter). In addition, mortality was increased 76 per cent in the group with albumin levels of 16 to 29 micrograms per milliliter and 37 per cent in the group with levels below 15. We conclude that microalbuminuria in patients with Type II diabetes is predictive of clinical proteinuria and increased mortality.

A simple artificial urine medium (AUM) has been developed which provides conditions similar to that found in human urine. AUM solidified with agar enabled the recovery of a wide range of urease-positive and -negative urinary pathogens. Liquid AUM supported growth at concentrations of up to 10(8) cfu ml-1, as found in normal urine. Reproducible, steady-state growth also occurred over many generations in continuous culture. AUM was capable of forming crystals and encrustations resembling those found in natural urinary tract infections. The medium is a suitable replacement for normal urine for use in a wide range of experiments modelling the growth and attachment of urinary pathogens in the clinical environment.