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Figure 12.12 shows results obtained during a glucose tolerance test on three people. The person represented by curve B was normal. The oral glucose load was given at time zero. It can be deduced that:
- Curve A is consistent with a diagnosis of diabetes mellitus.
- Curve C is more consistent with a diagnosis of an insulin-secreting tumour than of mal-absorption.
- A person showing curve B, who has glucose in the urine 30 minutes after glucose ingestion, is likely to have a low renal threshold for glucose
- The renal clearance of glucose two hours after glucose ingestion in patient A is nearer 10 than 30 per cent of the renal plasma flow, assuming a normal renal threshold.
- The renal clearance of glucose for the patient showing curve B is likely to be about 60 ml/minute 30 minutes after glucose ingestion.
Medicine
a. True The fasting glucose level and the peak level are markedly raised and there is delayed return of blood glucose to the fasting level.
b. False Curve C is typical of the flattening obtained with malabsorption; with an insulin-secreting tumour, the fasting level would tend to be low, with a more marked rise to a peak and a subsequent trough below the initial level.
c. True The normal renal glucose threshold is about 180 mg/100 ml (10 mmol/l).
d. True About 150/330 of the filtered glucose is being lost, corresponding to a clearance of 40–50 per cent of the GFR, i.e. about 60 ml which is about 10 per cent of renal plasma flow.
e. False Since blood glucose does not exceed the renal threshold for glucose, renal clearance will be zero.
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