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Unit 1 of 3 · B.Sc MLS Sem 5

Unit 1: Automation and function tests

Clinical Biochemistry-II notes · PTU syllabus (BMLS505-18)

3 min read6 topics10 exam questions
On this page
  1. Unit summary
  2. Automation in clinical biochemistry
  3. Glucose tolerance test
  4. Insulin tolerance test
  5. Xylose excretion test
  6. Gastric analysis
  7. Renal clearance tests
  8. Key terms
  9. Quick revision
  10. Important questions

Unit summary

Automation handles large workloads, and dynamic function tests reveal how organs respond to challenges. This unit covers automation in clinical biochemistry, the glucose tolerance test, insulin tolerance test, xylose excretion test, gastric analysis and renal clearance tests.

After this unit you can

  • Describe automation in clinical biochemistry
  • Perform and interpret the GTT and ITT
  • Explain the xylose test and gastric analysis
  • Calculate and interpret renal clearance

PTU syllabus topics

  • Automation in clinical biochemistry
  • glucose tolerance test
  • insulin tolerance test
  • xylose excretion test
  • gastric analysis
  • renal function clearance tests
ComparisonOral glucose tolerance test (75 g, WHO)
Fasting
2 hours after glucose

Normal

Under 100 mg/dL

Under 140 mg/dL

Impaired (prediabetes)

100–125 mg/dL

140–199 mg/dL

Diabetes

126 mg/dL or more

200 mg/dL or more

1

Topic 1

Automation in clinical biochemistry

ComparisonTypes of analysers
Principle
Examples

Continuous flow

Samples flow through tubing separated by air bubbles

Early AutoAnalyzer (historical)

Discrete analysers

Each sample in its own cuvette; random access

Most modern chemistry analysers

Centrifugal analysers

Centrifugal force mixes sample and reagents

Older batch systems

Dry chemistry

Reagents on slides or strips; reflectance

Vitros, point-of-care glucometers

Integrated and total lab automation

Chemistry and immunoassay modules with tracks, sorters, decappers

Large hospital laboratories

Key termsAdvantages and limitations
Advantages
High throughput, speed, precision, small volumes, fewer manual errors, LIS integration
Limitations
Cost, maintenance, need for skilled staff, carry-over, dependence on power and reagents
  • Steps automated: sample identification (barcodes), pipetting, reagent addition, incubation, measurement (photometry, ISE, immunoassay), calculation, flagging and reporting.
2

Topic 2

Glucose tolerance test

ProcessOral GTT (WHO)
  1. 1Unrestricted carbohydrate diet for 3 days; fast 8–14 hours
  2. 2Fasting blood sample
  3. 3Drink 75 g anhydrous glucose in 250–300 mL water over 5 minutes (children 1.75 g/kg)
  4. 4Rest; no smoking
  5. 5Blood at 2 hours (and at 30-minute intervals for a full curve)
ComparisonInterpretation (venous plasma)
Fasting
2-hour

Normal

Below 100 mg/dL

Below 140 mg/dL

Impaired (prediabetes)

100–125 mg/dL (IFG)

140–199 mg/dL (IGT)

Diabetes

126 mg/dL or more

200 mg/dL or more

  • Gestational diabetes (India, DIPSI): 75 g glucose without fasting; 2-hour value of 140 mg/dL or more. Abnormal curves: lag storage curve (rapid rise after gastrectomy or liver disease), flat curve (malabsorption, hypopituitarism).
3

Topic 3

Insulin tolerance test

  • Purpose: tests the pituitary–adrenal axis and growth hormone reserve; insulin-induced hypoglycaemia is a stress that should raise cortisol and GH. Done under close medical supervision.
  • Procedure: fasting patient, IV soluble insulin 0.1–0.15 U/kg; blood at 0, 15, 30, 45, 60, 90, 120 minutes for glucose, cortisol, GH. Adequate hypoglycaemia is glucose below 40 mg/dL. Normal: cortisol rises above about 18–20 µg/dL; GH above the cut-off. Contraindicated in heart disease and epilepsy.
4

Topic 4

Xylose excretion test

  • Principle: D-xylose is absorbed by the proximal small intestine without digestion and excreted unchanged in urine — tests intestinal absorption.
  • Procedure: fasting; 25 g D-xylose orally (5 g in some protocols); collect 5-hour urine (and blood at 1–2 hours). Normal: 5 g or more excreted in 5 hours (with 25 g dose). Low: coeliac disease, tropical sprue (mucosal disease); normal in pancreatic insufficiency — helps distinguish the causes of malabsorption. False lows in kidney disease and vomiting.
5

Topic 5

Gastric analysis

  • Purpose: measure gastric acid secretion — Zollinger–Ellison syndrome (very high), pernicious anaemia (achlorhydria), after vagotomy.
ProcessGastric analysis
  1. 1

    Fasting; pass a nasogastric (Ryle's) tube

  2. 2

    Aspirate the resting juice

  3. 3

    Collect basal secretion for 1 hour in 15-minute samples (BAO)

  4. 4

    Give pentagastrin stimulus

  5. 5

    Collect 1 hour (MAO, PAO)

  6. 6

    Titrate each sample with 0.1 N NaOH to pH 7 (or with Töpfer's reagent and phenolphthalein for free and total acidity)

Key termsResults
Basal acid output (BAO)
Normal up to about 5 mmol/hour
Maximum acid output (MAO)
About 10–40 mmol/hour
Achlorhydria
No acid after stimulation — pernicious anaemia, atrophic gastritis
Zollinger–Ellison
BAO above 15 mmol/hour; BAO/MAO ratio above 0.6; high gastrin
  • Largely replaced by serum gastrin, endoscopy and H. pylori tests.
6

Topic 6

Renal clearance tests

Key formulasClearance

  • Formula

    C = U × V ÷ P (U = urine concentration, V = urine flow mL/min, P = plasma concentration)

  • Creatinine clearance

    Normal about 90–140 mL/min

  • Urea clearance

    Standard about 54 mL/min; maximum about 75 mL/min

  • Body surface correction

    C × 1.73 ÷ patient's body surface area

Example

Urine creatinine 100 mg/dL, 24-hour urine 1,440 mL (1 mL/min), plasma creatinine 1.0 mg/dL: clearance = 100 × 1 ÷ 1.0 = 100 mL/min.

  • eGFR equations (CKD-EPI 2021) from serum creatinine now replace most timed collections. Inulin clearance is the reference GFR but impractical. Other renal tests: urine concentration and dilution, microalbumin (albumin–creatinine ratio).

Key terms

Discrete analyser
Analyser processing each sample separately
OGTT
Oral glucose tolerance test with 75 g glucose
Insulin tolerance test
Hypoglycaemia stress test of pituitary–adrenal function
D-xylose test
Test of small intestinal absorption
Clearance
Volume of plasma cleared of a substance per minute

Quick revision

  • Analyser types; advantages and limits; automated steps.
  • OGTT preparation and WHO criteria; GDM (DIPSI); abnormal curves.
  • ITT purpose, procedure, safety.
  • Xylose test interpretation; pancreatic vs mucosal malabsorption.
  • Gastric analysis BAO, MAO; clearance formula; eGFR.

Important exam questions

Practice questions written to the PTU exam pattern for this unit's syllabus: short answers (Section A style) and long answers (Sections B and C style).

Short-answer questions

  1. Q1.Name two types of chemistry analyser.
  2. Q2.What is the glucose load in an adult OGTT?
  3. Q3.Give the 2-hour OGTT value diagnostic of diabetes.
  4. Q4.What does the ITT assess?
  5. Q5.Why is the xylose test normal in pancreatic insufficiency?
  6. Q6.Calculate clearance for U = 80 mg/dL, V = 1.5 mL/min, P = 1.2 mg/dL.

Long-answer questions

  1. Q1.Describe automation in clinical biochemistry.
  2. Q2.Describe the oral glucose tolerance test and its interpretation.
  3. Q3.Describe the xylose excretion test and gastric analysis.
  4. Q4.Describe renal clearance tests.

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