Blood Test Results Explained: How to Read the Pattern

Opening a patient's blood results for the first time can feel like looking at a wall of numbers. Some are highlighted, some sit just outside the reference range and others look normal. The temptation is to scan for the red results and assume those are the important ones.

That is not how blood results work in practice.

A result is useful because of what it means for this patient, at this time. A mildly abnormal value may be normal for that person's usual baseline. A result still inside the laboratory reference interval may be concerning if it has changed quickly. The skill is therefore not simply recognising abnormal numbers. It is learning to read the pattern, trend and clinical context.

This guide gives you a repeatable way to approach a blood-results screen as a student nurse. It does not replace local policy, clinical assessment or discussion with your practice supervisor or registered clinician.

First: understand what you are looking at

A laboratory report usually gives you four pieces of information for each test:

• Test – what has been measured, for example haemoglobin or potassium.
• Result – the patient's measured value.
• Unit – how that value is expressed, such as mmol/L or g/L.
• Reference interval – the laboratory's expected interval for the relevant population and method.

The electronic record may also flag a result as high, low or critical. A flag is an alert to look more closely. It is not a diagnosis.

Reference intervals can differ between laboratories and may vary with factors such as age, sex, pregnancy and the analytical method used. This is why it is safer to use the interval displayed beside the patient's result rather than trying to memorise one universal set of 'normal values'.

The five-step method: Result → Trend → Patient → Sample → Action

When you open a set of blood results, work through them in the same order every time.

1. Result: what is actually abnormal?

Read the test name, exact result, unit and reference interval. Do not report 'the potassium is high' if you can report the actual value and unit.

Then look at the rest of the panel. Blood tests are often more useful as patterns than as isolated values.

2. Trend: what has changed?

Compare with previous results whenever they are available. Ask:

• Was this abnormal yesterday?
• Is it moving up or down?
• How quickly has it changed?
• What is this patient's usual baseline?

For example, a creatinine of 120 micromol/L cannot be interpreted properly from that number alone. A stable value around 120 may mean something very different from a rise from 60 to 120 over a short period.

3. Patient: does the result fit the clinical picture?

Now look away from the computer screen and back at the patient.

Consider the reason the bloods were requested, current symptoms, observations, fluid balance, urine output, medicines, recent procedures and relevant medical history. A laboratory result should support your assessment, not replace it.

If the patient looks acutely unwell, escalate the deterioration even if you have not yet seen an abnormal blood result.

4. Sample: could the result be misleading?

Unexpected results sometimes come from problems before the sample reaches the analyser. Examples include haemolysis, contamination from an intravenous infusion, an underfilled coagulation tube, a clotted sample or delayed transport.

But do not dismiss an unexpected result as 'just a bad sample'. Check any laboratory comment and discuss the result with the registered nurse or relevant clinician. If repeat bloods are required, follow the local plan.

5. Action: what happens next?

Your action depends on the result, the patient and your level of competence. As a student nurse, this will often mean recognising the concern, gathering relevant information and escalating promptly to your practice supervisor or registered clinician.

The NMC Code requires registered professionals to recognise worsening health, make timely referrals, ask for help when something is beyond their competence and raise safety concerns. These principles should also shape how students learn and practise under supervision.

Now apply the method to common blood panels

Full blood count (FBC)

An FBC is not one result. It is a group of measurements that includes red-cell, white-cell and platelet information.

When you open an FBC, a useful first scan is:

• Haemoglobin (Hb) – is there evidence of anaemia or a significant fall from baseline?
• White blood cell count (WBC) – raised or reduced counts need clinical context.
• Neutrophils – particularly important when assessing infection risk and marked neutropenia.
• Platelets – very low values may increase bleeding risk, while raised values have a range of possible causes.
• MCV and other red-cell indices – help describe the pattern of anaemia rather than diagnosing the cause on their own.

Example: Hb 104 g/L is flagged low. Yesterday it was 106 g/L and the patient is clinically stable. Compare that with Hb 104 g/L after a fall from 138 g/L alongside hypotension, tachycardia and possible bleeding. The number is the same; the clinical meaning is not.

For the detailed step-by-step guide, continue with Full Blood Count Explained for Student Nurses.

Urea and electrolytes (U&Es)

U&Es commonly include sodium, potassium, urea and creatinine, with estimated glomerular filtration rate (eGFR) often reported alongside creatinine in adults.

A useful first scan is:

• Sodium – consider both the degree of abnormality and how quickly it may have changed.
• Potassium – significant abnormalities can affect cardiac function and may require urgent assessment.
• Urea – interpret with creatinine, hydration and clinical context.
• Creatinine – compare with baseline rather than reading the value in isolation.
• eGFR – useful for assessment of kidney function but must be interpreted appropriately and is not the sole method for identifying acute kidney injury.

Example: potassium is reported as 6.2 mmol/L. Before deciding what it means, check the trend, kidney function, relevant medicines, the patient's condition and whether the laboratory has reported haemolysis. A potentially spurious result still requires appropriate review rather than being ignored.

For a deeper explanation, continue with Urea and Electrolytes Explained for Student Nurses.

Liver blood tests: learn to recognise the pattern

'Liver function tests' can be a misleading name because the panel contains markers that reflect different processes rather than one simple measurement of liver function.

Common components include bilirubin, alanine aminotransferase (ALT), alkaline phosphatase (ALP), albumin and, depending on the laboratory, gamma-glutamyl transferase (GGT).

Instead of asking 'Are the LFTs high?', ask which components are abnormal and which pattern is dominant.

Imagine the report shows ALT 420 U/L, ALP 145 U/L and bilirubin 24 micromol/L. If ALT is disproportionately raised compared with ALP, this is broadly a hepatocellular pattern. It tells you that hepatocellular injury is an important possibility, but it does not tell you the cause. Medicines, viral hepatitis, ischaemic injury and other conditions may need consideration by the clinical team.

Now imagine ALP 510 U/L, GGT 390 U/L and bilirubin 72 micromol/L, with a much smaller ALT rise. This is more suggestive of a cholestatic pattern. In the right clinical context, biliary obstruction is one possible cause, but again the blood results do not make the diagnosis.

For a student nurse, the useful next questions are practical: Is the patient jaundiced? Do they have right-upper-quadrant pain, fever, pruritus, pale stools or dark urine? What medicines are prescribed? Are the results new or longstanding? Has imaging or further assessment been requested?

Albumin needs separate thinking. A low albumin is not specific for liver disease and may occur with inflammation, malnutrition, renal protein loss and other conditions. Do not use albumin alone to decide that the liver is 'failing'.

Inflammatory markers

C-reactive protein (CRP) is commonly used as a marker of inflammation. It may rise with infection, but also with many non-infectious inflammatory processes.

Do not translate 'high CRP' into 'the patient has an infection'. Equally, a low or initially normal CRP does not safely exclude serious illness. Interpret it alongside the history, observations, examination findings and other investigations.

The trend can be particularly useful. A CRP moving from 40 to 180 mg/L alongside worsening observations means something different from a CRP steadily falling while the patient improves.

Glucose and ketones

Marked hypoglycaemia or hyperglycaemia can require prompt action, particularly when accompanied by altered consciousness, vomiting, dehydration or ketones.

Always establish what type of measurement you are viewing. A bedside capillary glucose result and a laboratory plasma glucose are obtained differently and should be interpreted within the relevant local pathway.

Coagulation: start with why it was requested

Common coagulation tests include prothrombin time (PT), activated partial thromboplastin time (APTT), international normalised ratio (INR) and fibrinogen.

Before interpreting an abnormal result, ask why the test was requested and whether the patient is taking an anticoagulant. An INR is routinely used to monitor warfarin therapy, whereas PT and APTT can be prolonged for several different reasons. The pattern may be influenced by anticoagulant medicines, liver dysfunction, vitamin K deficiency, factor deficiencies, inhibitors and consumptive coagulopathy.

For example, an INR of 3.0 means very different things in a patient deliberately anticoagulated with warfarin to a prescribed therapeutic target and in a patient who is not taking warfarin and has new bleeding. The number cannot be interpreted safely without the indication, medicine history, target range where relevant and clinical picture.

If coagulation results are unexpectedly abnormal, also consider sample quality. Citrate tubes need the correct blood-to-anticoagulant ratio, so significant underfilling can affect results. Follow local policy and laboratory advice if repeat sampling is required.

Why the trend can matter more than the flag

Imagine two patients both have a creatinine of 120 micromol/L.

Patient A: previous creatinine values have been around 115–125 micromol/L for months and the patient is clinically stable.

Patient B: creatinine was 62 micromol/L recently, urine output has fallen and the patient has become acutely unwell.

The same result has a very different meaning because the baseline, rate of change and clinical picture are different.

This is one reason acute kidney injury is assessed using changes in creatinine and urine output rather than simply asking whether creatinine is outside a laboratory reference range.

Common sample problems you should recognise

Haemolysis

Red cells can rupture during or after collection, releasing intracellular contents into the sample. This can alter several measurements and is a well-recognised reason for a falsely raised potassium result.

Sampling near an intravenous infusion

A specimen collected from an inappropriate site around an infusion may become diluted or contaminated by the infused fluid or medicine.

Clotted samples

A sample that should have remained anticoagulated may clot and become unsuitable for particular analyses, including components of an FBC.

Incorrectly filled coagulation tubes

Coagulation testing depends on the correct blood-to-anticoagulant ratio, so an underfilled tube can produce unreliable results.

If a result does not make sense, investigate the possibility of a sample problem, but never use that possibility as a reason to delay escalation of a potentially serious result.

Three mini scenarios: what would you notice?

Scenario 1: the falling haemoglobin

A patient's Hb is 96 g/L. Yesterday it was 118 g/L. They are pale, their heart rate has increased and their blood pressure is lower than earlier.

What matters? Not simply that the Hb is below the reference interval. The significant fall plus the patient's observations and appearance requires prompt escalation and assessment for a cause such as bleeding.

Scenario 2: the high potassium

A potassium result returns at 6.1 mmol/L. Yesterday it was 4.4 mmol/L. The laboratory comment states that the specimen is haemolysed.

What matters? Haemolysis may have affected the result, but the potassium should not simply be ignored. Report the result and laboratory comment promptly and follow the clinical plan, which may include urgent reassessment and repeat sampling.

Scenario 3: the 'normal' creatinine

A patient's creatinine is still within the laboratory reference interval, but it has risen substantially from their recent baseline. Their urine output has also fallen.

What matters? A value does not need to be flagged high to represent clinically important deterioration. The change from baseline and urine output are important.

How to escalate a blood result properly

Compare these two handovers:

Less useful: “Mrs Khan's bloods are bad.”

More useful: “Mrs Khan's potassium is 6.2 mmol/L. It was 4.7 yesterday. The sample is not reported as haemolysed. Her creatinine has also risen, her urine output has fallen and I am completing a current set of observations.”

The second version gives the clinician something they can act on.

When escalating, be ready to give:

• the patient's identity;
• the exact result and unit;
• the previous result or baseline;
• the date and time of the sample;
• relevant observations and symptoms;
• relevant urine output or fluid-balance information;
• any laboratory comment, such as haemolysis;
• what has already been done.

Using an SBAR structure can help you communicate this information clearly.

What should make you escalate promptly?

Local laboratories and organisations have their own critical-result pathways, so there is no single list of numbers that a student should memorise and apply everywhere.

Prompt escalation is appropriate when:

• the laboratory identifies a result as critical;
• there is a substantial or rapid change from the patient's baseline;
• the result fits a deteriorating clinical picture;
• there is significant hypo- or hyperkalaemia or another major electrolyte disturbance;
• there is significant hypoglycaemia or severe hyperglycaemia with concerning features;
• haemoglobin is falling significantly, particularly with possible bleeding;
• platelets or neutrophils are markedly reduced;
• kidney function is deteriorating or urine output is falling;
• you are concerned about the patient even if the laboratory results have not yet become abnormal.

Your role as a student nurse

You are learning to recognise and interpret clinical information, not to diagnose a patient from a blood-results screen.

A strong student response is:

“I have noticed this result has changed. I have checked the trend and the patient. This is what I have found, and I think it needs reviewing.”

That demonstrates much more clinical reasoning than simply memorising reference ranges.

Use blood results as one part of the whole assessment. Work within your competence, use your supervision appropriately, protect confidentiality, document according to local policy and escalate concerns without unnecessary delay.

A simple way to remember it

When you are staring at a result screen and do not know where to begin, remember:

Result → Trend → Patient → Sample → Action.

What is the result? What has changed? Does it fit the patient? Can you trust the sample? What needs to happen next?

If you can answer those five questions, you are no longer just reading numbers. You are beginning to use the results as part of clinical assessment.

References

National Institute for Health and Care Excellence (NICE) (2024) Acute kidney injury: prevention, detection and management (NG148). Available at: NICE NG148 

National Health Service (NHS) (n.d.) Blood tests. Available at: NHS blood tests 

Nursing and Midwifery Council (NMC) (2018, updated 2025) The Code: Professional standards of practice and behaviour for nurses, midwives and nursing associates. Available at: NMC Code 

Association for Laboratory Medicine (n.d.) Lab Tests Online UK: Tests A to Z. Available at: Lab Tests Online UK 

British Society of Gastroenterology (2018) Guidelines on the management of abnormal liver blood tests. Gut, 67(1), pp. 6–19. Available at: British Society of Gastroenterology guideline 

British Society for Haematology (n.d.) Guidelines. Available at: British Society for Haematology guidelines