Clinical Reference

Understanding Blood Results: A Student Nurse’s Practical Guide

Log into any hospital system and you’ll see pages of numbers. This guide turns them into meaning — what each result means, when to worry, and exactly what to do next.

“Treat the patient, not the numbers. A lab value tells you what is happening in the blood — your clinical assessment tells you what is happening to the person.”

— The Golden Rule of Ward Nursing

Important: Exact reference ranges can vary slightly between hospital labs. Always cross-check against your trust’s own values — these are the standard UK ranges you’ll see almost everywhere.

1. Full Blood Count (FBC)

Collected in a purple-top EDTA tube. Checks red cells, white cells, and platelets — your oxygen transport, immune defence, and clotting all in one test.

Haemoglobin (Hb)

Reference: Male 130–180 g/L | Female 120–160 g/L

Carries oxygen to every tissue. Low = anaemia: look for tiredness, pale skin, breathlessness, fast pulse. Causes include blood loss, iron deficiency, or chronic illness. High: dehydration, lung disease, or smoking — blood becomes thick and harder to pump.

White Blood Cells (WBC)

Reference: 4.0–11.0 × 10⁹/L

Your immune system at work. High: infection, inflammation, surgery, or steroids. Low: higher risk of infection — check if they’re on chemotherapy or have bone marrow issues. Report immediately if very low.

Platelets (Plt)

Reference: 150–400 × 10⁹/L

Essential for clotting. Low: watch for bruising, bleeding gums, petechiae — could be sepsis, liver disease, or reaction to medication. High: can rise after infection or surgery; increases clot risk.

2. Urea & Electrolytes (U&Es)

Collected in a gold-top or green-top tube. Checks how well the kidneys are working and whether the body has the right fluid balance.

Sodium (Na⁺)

Reference: 135–145 mmol/L

Controls fluid balance and brain function. Low: confusion, drowsiness, cramps — common with diuretics or too much fluid. High: dehydration — check mouth, skin turgor, fluid intake.

Potassium (K⁺) — ⚠️ Critical

Reference: 3.5–5.0 mmol/L

Directly affects the heart rhythm. Above 5.5: risk of dangerous arrhythmias — urgent review. Below 3.5: muscle weakness, tiredness, cramps — common with diuretics or vomiting.

🚨 Red Flag: Below 3.0 or above 6.0 = tell someone immediately and request an ECG.

Urea

Reference: 2.5–7.8 mmol/L

Waste product from protein. Rising: could mean dehydration, bleeding from the gut, or kidneys slowing down. Check their fluid intake and output.

Creatinine & eGFR

Creatinine: 45–110 μmol/L | eGFR: >90

The best measure of kidney function. Rising creatinine + falling eGFR: kidney injury — monitor urine output hourly, report trends. Compare with their previous results to see if this is new or long-term.

3. Liver Function & Infection Markers

C-Reactive Protein (CRP)

Reference: <5 mg/L

General inflammation signal. Rising fast = infection or tissue damage. Falling = treatment working. Always read alongside the patient — a high CRP means nothing without checking how they look and feel.

Bilirubin

Reference: 3–21 μmol/L

Breakdown product from old blood cells. High: yellow skin/eyes, dark urine, pale stools — could be liver disease or blocked bile duct.

Liver Enzymes (ALT & ALP)

ALT: 10–50 U/L | ALP: 30–130 U/L

ALT: rises when liver cells are damaged — infection, medication, or alcohol. ALP: rises when bile flow is blocked or in bone conditions. Look at the whole pattern, not just one number.

4. Blood Gases (ABGs) — Simple Framework

Taken from an artery — tells you how well the lungs and body chemistry are balanced. Don’t panic — just follow these four steps in order:

🫁 The 4-Step ABG Cheat Sheet

1. Check pH (7.35–7.45)

Below 7.35 = too acidic | Above 7.45 = too alkaline

2. Check PaCO₂ — Respiratory

High = lungs not clearing enough CO₂ | Low = breathing too fast/deep

3. Check HCO₃⁻ — Metabolic

Low = body too acidic (kidneys, diabetes, shock) | High = body retaining too much base

4. Check PaO₂ — Oxygen Levels

Low = give oxygen, reassess, escalate if not improving

5. What to Do When a Result Is Abnormal

Spotting the number is only half the job. Here’s exactly what to do next:

Go see the patient. Don’t just look at the screen. Do a quick A–E assessment and check their observations yourself.
Compare with previous results. Is this new or their normal? A sudden change matters far more than a long-term pattern.
Tell your supervisor. Say what you’ve seen and what you’ve already checked.
Escalate clearly. Use SBAR: Situation, Background, Assessment, Recommendation — exactly what you need, not just “the bloods are off.”
Write it down. Result, time, who you told, what they said. Your note protects you and guides the next shift.

Speak Up With Confidence

How to escalate concerns clearly using SBAR — exactly what to say and when.

Learn SBAR →

Master Clinical Assessment

Full head-to-toe guide — turn numbers into real patient understanding.

Read the Guide →

Clinical Reference

Written by: Daniel Hancock, Registered Nurse

Clinical focus: Haematology, renal function, interpretation, escalation, SBAR communication

Published: September 2026 | Last clinically reviewed: September 2026

Checked against: UK standard reference ranges, Royal College of Nursing guidance, local trust policy alignment

⚠️ For supervised student learning only. Follow local trust policy, prescription instructions and the direction of the registered nurse or medical team. This page does not replace emergency protocols. Reference ranges may vary by laboratory — always cross-check your trust’s current values.