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Laboratory investigations

How each common test panel works, its reference ranges, what raises or lowers it, and worked sample result sheets read step by step.

23 topics published

Introduction

Laboratory medicine is where a clinical question becomes a number. Most decisions in hospital medicine lean on a blood count, a chemistry panel or a fluid analysis, and reading these results well is a skill of its own.

Each topic covers one test or panel: what it measures, its reference ranges, what raises or lowers it, and what to do next. Every topic also holds worked sample result sheets, original and labelled illustrative, read step by step.

How to study laboratory investigations

Begin with the topic on reading a report, then take the panels you meet most often: blood count, kidney, liver, electrolytes.

For each sample sheet, cover the interpretation and read the numbers first. Say the pattern aloud, then check it against the worked answer.

Reference ranges differ between laboratories and countries. Learn the range printed on your own laboratory report, and treat the ranges here as examples with their sources.

Contents by part

The topics below are in teaching order. Each part builds on the one before it.

  1. How to read a report. Start here: what the units, ranges and flags on any report mean.
  2. Blood counts, clotting and iron. The cell counts, the clotting screen and the iron, B12 and folate tests behind most anaemia and bleeding questions.
  3. Chemistry panels. The routine biochemistry: kidney, liver, electrolytes, bone, glucose, lipids and thyroid.
  4. Cardiac, inflammatory and immune markers. Markers of heart injury, inflammation, autoimmunity and cancer.
  5. Urine, stool and body fluids. Tests on urine, stool and the fluids drawn from the spine, chest, abdomen and joints.
  6. Microbiology. Reading a Gram stain, a culture and a sensitivity report.

Topics

  2. Full blood count and blood film

    Read a full blood count and blood film: red cells, haemoglobin, indices, white cells, platelets, reticulocytes, patterns, sample sheets and pitfalls.
    Checked against sourcesVerified 31 October 2026

  5. Vitamin B12 and folate: tests and interpretation

    How to read serum B12, active B12, homocysteine, methylmalonic acid, serum and red-cell folate, and parietal cell and intrinsic factor antibodies.
    Checked against sourcesVerified 31 October 2026

  6. Renal function tests: urea, creatinine and eGFR

    How urea and creatinine are formed and cleared, how to read kidney function from them and from eGFR, and how to stage and interpret renal disease.
    Checked against sourcesVerified 31 October 2026

  4. Glucose, HbA1c and tests for diabetes

    Glucose and HbA1c tests for diabetes: fasting and random glucose, OGTT, ketones, C-peptide, fructosamine and time in range.
    Checked against sourcesVerified 31 October 2026

  7. Arterial blood gas and acid-base result sheets

    How to read an arterial blood gas: ranges, flags, stepwise interpretation, compensation, anion gap, delta ratio, oxygenation and venous samples.
    Checked against sourcesVerified 31 October 2026

  10. Autoantibodies and tumour markers

    Autoantibodies and tumour markers: what they show, what ranges count, and how to read them without over-interpreting them.
    Checked against sourcesVerified 31 October 2026