Why is glucose normally absent from urine?

The kidney tubules reabsorb all the filtered glucose while blood glucose is normal. Glucose appears in urine only when blood glucose exceeds the renal threshold of about 10 mmol/L.

A patient's fasting plasma glucose is 8.2 mmol/L. What might this indicate?

A fasting plasma glucose of 7.0 mmol/L or more suggests diabetes mellitus. The result would normally be confirmed by a repeat test or an HbA1c measurement.

How are sodium and potassium measured in blood by an analyser?

Modern analysers use ion-selective electrodes, each responding to one kind of ion. The voltage across each electrode depends on the concentration of that ion in the sample.

CCEA A-Level Life and Health Sciences 0008

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Histology and Pathology

Clinical biochemistry tests and electrophoresis

3 things to know
A2 8

Overview

Glucose by glucose oxidase and urine strips, sodium and potassium and their reference ranges, cholesterol testing, serum protein and haemoglobin electrophoresis, and the biomedical scientist's skills.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is the role of the clinical biochemistry department, and which specimens does it test?

Key term

How is glucose measured in a blood sample using glucose oxidase?

Key term

How is urine tested for glucose with a reagent strip?

Questions from this subtopic

Each one with the model answer underneath.

1
What is the role of the clinical biochemistry department, and which specimens does it test?
Model answer
Clinical biochemistry measures chemicals in body fluids to help diagnose and monitor disease. Most tests use serum or plasma, and others use urine or cerebrospinal fluid.
2
How is glucose measured in a blood sample using glucose oxidase?
Model answer
Glucose oxidase converts glucose to gluconic acid, releasing hydrogen peroxide. Peroxidase then uses the peroxide to form a coloured dye, whose absorbance shows the glucose concentration.
3
How is urine tested for glucose with a reagent strip?
Model answer
The strip is dipped in fresh urine and the pad read against a colour chart after a set time. The pad contains glucose oxidase and peroxidase, so it changes colour only with glucose.
4
Why is glucose normally absent from urine?
Model answer
The kidney tubules reabsorb all the filtered glucose while blood glucose is normal. Glucose appears in urine only when blood glucose exceeds the renal threshold of about 10 mmol/L.
5
A patient's fasting plasma glucose is 8.2 mmol/L. What might this indicate?
Model answer
A fasting plasma glucose of 7.0 mmol/L or more suggests diabetes mellitus. The result would normally be confirmed by a repeat test or an HbA1c measurement.
6
How are sodium and potassium measured in blood by an analyser?
Model answer
Modern analysers use ion-selective electrodes, each responding to one kind of ion. The voltage across each electrode depends on the concentration of that ion in the sample.

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