All pathways
Reasoning GP · Pathways

Lab results — abnormal blood tests

One place for any abnormal blood result. Start from the test, then open the structured pathway for that abnormality — investigation, red flags, and management, anchored to NICE CKS and UK specialty guidance. Covers the common FBC, haematinics, U&E, LFT, bone, thyroid, hormone, lipid and glucose abnormalities — plus inflammatory, immune and tumour markers — seen in primary care.

52 / 52 result pathways

A safe approach to any abnormal result

Work top to bottom. Step 1 is a hard gate — clear the critical ("panic") values first, before you reason about whether the result is even real.
1
Exclude a critical value — admit first, verify secondSame-day / emergency gate

Some results mandate immediate hospital admission or same-day specialist discussion — even if the patient is asymptomatic, and even if you strongly suspect the sample is spurious (haemolysed, drip-arm, delayed transit). Act on the number first: phone the on-call medical team or send to ED, then arrange the repeat. Never sit on a critical value waiting for a recheck.

K⁺ ≥ 6.5 (or ≥ 6.0 with ECG changes) — severe hyperkalaemia → ECG + emergency admission
K⁺ ≤ 2.5 — severe hypokalaemia → admit (arrhythmia risk)
Na⁺ < 120 or > 155, or any acute/symptomatic change → admit
Adjusted Ca²⁺ ≥ 3.0 (crisis) or symptomatic — admit for IV fluids
Glucose < 3.0 (hypo) or DKA / HHS picture → emergency
Neutrophils < 0.5 — neutropenic sepsis risk; if febrile/unwell → 999
Platelets < 20 (or active bleeding) → same-day haematology
Hb < 70, or symptomatic anaemia → urgent admission/transfusion
New pancytopenia / blasts on film → same-day haematology
Adjusted Ca²⁺ < 1.9, Mg < 0.4, or PO₄ critically low → admit
AKI with hyperkalaemia / fluid overload / oliguria → admit
Paracetamol above treatment line, or INR > 8 with bleeding → emergency

Local lab "critical/panic" phone-alerts always override this list — if the lab rings you, treat it as an emergency until proven otherwise.

NO critical value — now reason about the result
2
Is it real?Confirm before acting (non-emergencies)

Repeat/confirm; consider spurious or pre-analytical causes — haemolysis, drip-arm contamination, sample timing, dehydration, EDTA effect.

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3
What's the trend?Old results & rate of change

Compare with previous values — an acute change matters far more than a stable long-standing one; note the rate of change.

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4
How severe / urgent?Severity bands

Use severity bands and red-flag thresholds to decide same-day vs routine action.

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5
Clinical contextTreat the patient, not the printout

Symptoms, drugs, comorbidity and ICE — interpret the number against the whole person.

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6
Action & safety-netPlan + recheck

Investigate, refer or monitor; document the plan, the safety-net, and exactly when to recheck.

No result matches that search. Try a test name (sodium, potassium, calcium, Hb, platelets, LFTs, TSH).
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Full Blood Count (FBC)

FBC15
🩸Anaemia (low Hb)Microcytic / normocytic / macrocytic work-up; cancer red flagsLow haemoglobin→ 🩸Iron deficiencyIsolated low ferritin or IDA · finding the cause · oral/IV ironLow ferritin→ 🩺PolycythaemiaRaised Hb / Hct · primary vs secondary · JAK2High haemoglobin / Hct→ 🔬LeucocytosisRaised WCC · reactive vs haematological causesHigh white cells→ ⚪LeucopeniaLow WCC · neutropenia · drug causes · when to act urgentlyLow white cells→ 🩸ThrombocytopeniaLow platelets · ITP · bleeding risk · urgent thresholdsLow platelets→ 🔴ThrombocytosisRaised platelets · reactive vs essential · cancer associationHigh platelets→ 🟣Easy / unexplained bruisingCoagulation & platelet work-up · when to worryClotting / platelets→ 🔬MacrocytosisHigh MCV · B12/folate · alcohol · MDS · hypothyroidHigh MCV→ 🩸MicrocytosisLow MCV · iron deficiency · thalassaemia · ACDLow MCV→ 🦠LymphocytosisHigh lymphocytes · CLL · EBV · pertussisHigh lymph→ 🧬LymphopeniaLow lymphocytes · HIV · steroids · CVIDLow lymph→ 🩸PancytopeniaAll cell lines low · marrow failure · AML/MDS · urgentAll lines low→ 🩸Normocytic anaemiaACD vs early IDA · haemolysis (retic/DAT) · CKD · marrow failure · TTPNormal MCV→ 🔬EosinophiliaHypereosinophilic syndrome · EGPA (Churg-Strauss) · parasites/strongyloides · DRESS · atopyHigh eosinophils→
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Haematinics (B12 · Folate · Iron)

Haematinics4
🩸Low ferritinIron deficiency · GI workup · oral/IV iron · coeliac · menorrhagiaLow ferritin→ 🧬Vitamin B12 deficiencyPernicious anaemia · neuro SACD · IM hydroxocobalamin · metforminLow B12→ 🔴High ferritinHLH (>10,000) emergency · haemochromatosis C282Y/transferrin sat · venesection · HCC surveillance · DIOSHigh ferritin→ 🥦Low folateCheck B12 BEFORE treating (SACD risk) · MTX 5mg weekly · periconception 400mcg vs 5mg · coeliac · valproateLow folate→
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Urea & Electrolytes / Renal

U&E7
🧂HyponatraemiaNa⁺ <135 · volume status · SIADH · drug causesLow sodium→ ⚡HypokalaemiaK⁺ <3.5 · causes · ECG risk · replacementLow potassium→ ⚡HyperkalaemiaK⁺ >5.5 · ECG changes · ACEi/ARB · CKD · Addison's · calcium gluconateHigh potassium→ 🩺Acute kidney injuryRising creatinine / falling eGFR · NG148 · sick-day rulesRaised creatinine→ 🫘Chronic kidney diseaseeGFR staging · ACR · NG203 · referral thresholdsLow eGFR→ 🔋HypomagnesaemiaPPI-induced · refractory hypokalaemia · QT · torsadesLow Mg→ 💧HypernatraemiaNa⁺ >145 · correct ≤0.5 mmol/L/h (chronic) · Na >160 999 · diabetes insipidus · lithium NDI · HHSHigh sodium→
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Liver Function Tests

LFT3
🧪Abnormal LFTsHepatocellular vs cholestatic · liver screen · FIB-4Deranged LFTs→ 🫀Fatty liver diseaseMASLD/ALD · fibrosis staging (FIB-4/ELF) · surveillanceRaised ALT + steatosis→ 🟡JaundiceRaised bilirubin · pre/intra/post-hepatic · urgent pathwaysHigh bilirubin→
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Bone Profile / Calcium

Bone5
🧪HypercalcaemiaCorrected Ca >2.6 · PTH · hyperparathyroidism vs malignancyHigh calcium→ 🦴HypocalcaemiaCorrected Ca <2.2 · tetany/seizure 999 · PTH · vitamin D · QT prolongationLow calcium→ 🦴Abnormal bone profileCalcium · PTH · Paget's · osteomalacia · raised ALPBone profile→ ☀️Vitamin D deficiency25-OH-D · loading regimen · osteomalacia · ricketsLow vit D→ 🦴Malignant hypercalcaemiaCorrected Ca · IV saline rehydration · single IV bisphosphonate · poor-prognosis markerHigh calcium (malignancy)→
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Thyroid Function Tests

TFT5
🦋HyperthyroidismSuppressed TSH · Graves / nodular · BTA pathwayLow TSH→ 🦋HypothyroidismRaised TSH · overt & subclinical · levothyroxine titrationHigh TSH→ 🦋Abnormal TFTsTSH interpretation · Graves · Hashimoto · pregnancy · subclinicalTFTs→ 🦋Subclinical hypothyroidismRaised TSH, normal T4 · TSH ≥10 vs <10 · treat / trial / monitor · NICE NG145Raised TSH, normal T4→ 🤰Thyroid dysfunction in pregnancyTrimester ranges · levothyroxine ↑30–50% early · PTU · urgent endocrine + antenatal referralTFTs in pregnancy→
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Hormones / Endocrine

Hormones3
🧔Testosterone deficiencyTwo morning levels · LH/FSH · pituitary exclusion · TRT · prostate surveillanceLow testosterone→ 🔬HyperprolactinaemiaProlactinoma · pituitary MRI · macroprolactin (PEG) · cabergoline · drug-inducedHigh prolactin→ ⚕️Female hormone abnormalitiesPOI (FSH >25) HRT essential · PCOS Rotterdam · day-21 progesterone · virilising tumour (testosterone >5) 2WW · pituitary apoplexyFSH/LH/oestradiol→
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Lipids & Glucose

Metabolic4
🫀High cholesterolLipid profile · QRISK · statins · FHRaised lipids→ 🩸Type 2 diabetes (high HbA1c)Diagnosis · organ-protective first choices · reviewHigh HbA1c→ 🔴High triglyceridesPancreatitis risk · metabolic syndrome · fibrates · EPAHigh TG→ 🍬HypoglycaemiaLevel 3 → 999 / IM glucagon · sulfonylurea hypo = 24–48h obs · 15-15 rule · review driversLow glucose→
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Inflammatory, Immune & Tumour Markers

Markers5
🔥Raised CRP / ESRSepsis · GCA same-day · PMR · myeloma · vasculitisHigh CRP/ESR→ 🧬Abnormal immunoglobulinsMGUS · myeloma CRAB · serum FLC · CVID · paraproteinIgs / paraprotein→ 🔬Abnormal tumour markersPSA · CA125 RMI · CEA · AFP · 2WW thresholdsTumour markers→ 🔬Raised PSAAge-adjusted thresholds · mpMRI before biopsy (NG131) · malignant DRE → 2WW · ADT · MSCCHigh PSA→ 🧬Allergy test abnormalitiesSensitisation vs clinical allergy · sIgE needs history · tryptase/mastocytosis · penicillin de-labelling · OAS · venom immunotherapyIgE / tryptase→
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Muscle Enzymes

Muscle1
💪Raised creatine kinase (CK)ULN multiples · rhabdomyolysis (>50× / AKI) · statin myopathy · necrotising myositis · secondary causesHigh CK→
Educational use only. These pathways support clinical reasoning and SCA preparation; always verify against the live NICE CKS, your local laboratory reference ranges and prescribing formulary, and act on the whole clinical picture rather than an isolated value.