As a doctor in training, one of my tasks was to boil urine. Medical wards used to have a row of glass test-tubes to hold urine, and every morning we would light up a spirit lamp. All patients in the ward had their urine samples, that we were meant to boil. In a short span of hours, a list would be ready for the attending consultant carrying names, and if their urine had any sugar or protein. This routine went on day after day, on all the days of the medical training. Those with diabetes had multiple samples, for us to boil. So, it was a pleasant surprise to find boiled urine depicted on a postage stamp.
Benedict’s test
The rigor for urine sugar estimation was described around 1908 by an American chemist Stanley Rossiter Benedict. He invented a blue colored mixture of sodium carbonate, sodium citrate and copper sulfate. This mixture is called Benedict’s reagent. As a medical student we had to remember the rigor; eight drops of urine, added to 5ml of Benedict’s reagent – Not a drop or ml more or less. When it was boiled, and if the color stayed blue, meant there is no sugar. When color changed to Green, Greenish-yellow, Orange or Red, it meant more sugar in urine, graded from 1+ to 4+.
From drops to strips
Kidneys filter blood, and would normally excrete sugars above a threshold of around 180mg/dL. Thus, higher sugar levels in urine mean higher levels in blood. As testing sugar in blood was tough, Benedict’s test became popular to screen for diabetes, and stood the test of time for decades. In 1956, we saw emergence of dry chemistry. Another American Chemist Alfred Free could impregnate glucose oxidase enzyme on a piece of paper. When dipped in urine, the paper strip changed color if it had more sugar. Later, multiple such enzymatic strips (for example for sugar, protein, and ketones) could be placed on a single strip and dipstick testing began to replace Benedict’s test.
Despite urine dipstick innovation of 1960s, it became more widely used in India only in 1990s. Maybe it was cost, or insistence that urine sugar must be tested by a difficult way. When available, dipsticks were considered a scarce resource, and we frequently would longitudinally cut a strip in two, so that we could test two samples from the same strip. Regardless, of this constraint, world was moving away from urine based tests. This was because we realized that these did not accurately reflect occurrence of diabetes.
Blood takes over
Dextrose-sticks were invented in 1970s, and by 1990s, digital glucometer had arrived.
Initially the blood glucose testing strips and meters still had a cost, and we would use these sparingly and only in critically ill. However, over past two decades their use has tremendously expanded. This is made possible by reduced cost, and increased awareness about value of blood glucose levels. Today finger-prick blood sugar testing as become a norm, not only for all medical trainees, but also for nurses, paramedics, midwives, and even front-line health workers.
Urine sugar testing is dying. More accurate blood sugar has taken over. Some newer drugs for diabetes now control blood glucose by excreting more sugar in urine, and the relation between the two has become even murkier. So, glucometers have replaced test-tubes, finger prick dominates over urine collection, and we have more testing strips in the waste-bin than boiled urine down the sink.
