SERUM INORGANIC PHOSPHORUS IN THE DIAGNOSIS OF DIABETES MELLITUS

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Abstract
THE oral or intravenous administration of glucose to normal individuals produces a temporary depression in the serum level of inorganic phosphorus. It has been suggested (1, 2) that the measurement of this phosphorus fall during the performance of glucose tolerance tests may be a valuable adjunct in the discovery of cases of early, latent, or so-called pre-diabetes mellitus. The importance of recognizing diabetes early in its course has received recent emphasis and any laboratory refinement which may facilitate its diagnosis requires careful evaluation. METHODS Serum inorganic phosphorus was determined during the performance of intravenous glucose tolerance tests in 28 normal controls who were internes, residents, medical students or student nurses and in 24 patients with diabetes mellitus selected from the outpatient diabetic clinic. Fourteen of the latter group were extremely mild diabetics, i.e., they had not required insulin within the past five years, their fasting blood sugars ranged from normal to 175 mg./100 cc. and their 24-hour urine specimens were usually free of reducing substances. Most of them exhibited hyperglycemia and glycosuria only during periods of stress. Ten were classified as moderately severe diabetics because they had always required insulin, their fasting blood sugars were frequently elevated and glycosuria was often present. No special preparatory diet was prescribed prior to the test but it was ascertained that the previous diet was adequate. Tests were performed in the morning after an overnight fast. One-third gram of dextrose per kilogram of body weight in a 50 per cent aqueous solution was injected intravenously within 3 to 5 minutes and 0.1-cc. capillary blood specimens were obtained 15, 30, 60, 75, 90 and 120 minutes thereafter (3). True blood sugar was determined by the Lauber-Mattice method (4) and read on a Klett-Summerson photoelectric colorimeter. Duplicate specimens showed an average error of ± 1.4 mg. and a range of 0–6 mg. Serum inorganic phosphorus was determined before, and one and two hours after the glucose injection (5). In previous studies we ascertained that the maximum phosphate fall would occur within this time interval. Blood specimens showing any gross hemolysis were discarded. In 10 normal subjects phosphate was similarly measured after the intravenous injection of 50 cc. of normal saline solution In an additional 15 normal subjects serum inorganic phosphorus was measured before and 15, 30 and 60 minutes after the intravenous injection of Lilly's crystalline insulin in doses varying from 0.025 to 0.1 unit per kilogram of body weight.

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