Abnormal Blood Test Results: What to Do Next

Your report has flags. Most guides tell you what the flags mean. This one tells you what to actually do — from the moment you open the results to the point where you have a clear action plan.

Medically reviewed by Dr. Prahlad Rai Gupta, MBBS, MD (Pulmonary Medicine)

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Covers standard and critically flagged results Urgency tiers with concrete timelines

Three urgency tiers — and the right response for each

Not every flag needs the same response. The critical distinction is between a critical value, a significantly abnormal result, and a borderline flag worth monitoring.

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Critically abnormal values
Results so far outside range they indicate potential immediate medical risk. Labs flag these separately from standard H/L tags — often with different colour, exclamation mark, or a call from the ordering clinician.
Typical examples
  • Potassium below 2.5 or above 6.5 mmol/L
  • Sodium below 125 or above 155 mmol/L
  • Haemoglobin below 7.0 g/dL
  • Creatinine more than 2–3× the upper limit
  • Platelet count below 20 × 10⁹/L
Schedule within 1–2 weeks
Significantly abnormal results
Results meaningfully outside the range on markers reflecting organ function, or results that explain active symptoms. Warrant GP appointment and possibly follow-up testing, but are not emergencies.
Typical examples
  • TSH above 10 mIU/L with fatigue symptoms
  • ALT or AST more than 3× the upper limit
  • eGFR below 45 mL/min/1.73m²
  • Ferritin below 15 ng/mL with active fatigue
  • HbA1c above 48 mmol/mol (6.5%)
Monitor at next test
Mildly abnormal / borderline flags
Borderline results on markers with no matching symptoms, or flags that are statistically common and likely to return to normal on repeat testing. Monitor at the next routine blood test rather than acting immediately.
Typical examples
  • Lymphocyte count 2% below the lower limit
  • MCV 1–2 fL outside the upper limit
  • LDL 10–15% above the upper limit, no symptoms
  • Basophils slightly elevated, no other flags
  • Eosinophils mildly elevated, no allergic symptoms

Six steps after getting your results

Work through these in order. Steps 1 and 2 take 5 minutes. Steps 3 and 4 determine whether you need medical contact or can act independently.

1
Check for critical flags first
Scan the report for results displayed differently from standard H/L tags — different colour, exclamation mark, or a "critical" note. These require same-day contact with your GP or an urgent care clinic. Do not wait to book a routine appointment. If you're unsure whether a result is a critical value, call your GP surgery and read the result over the phone; they can advise immediately.
If no critical flags: continue to step 2. Critical values are rare — most flagged results are standard H/L deviations, not critical values.
2
Count the flags and calculate each deviation
List every flagged result and calculate percentage deviation for each: (your value − range boundary) ÷ range boundary × 100. This turns "I have six flags" into a ranked list. A 2% deviation and a 60% deviation are both "H" on the report. They are not the same thing.
Reference: for context on having multiple flags simultaneously, see Multiple Abnormal Blood Test Results — statistically, having 1–3 flags on a 20-marker panel is common even in healthy people.
3
Match flags against your symptoms
Go through each flagged result and ask: does this explain anything I'm currently experiencing? Fatigue, hair shedding, cold intolerance, brain fog, breathlessness, poor recovery, weight changes — all of these connect to specific markers. A flag that explains active symptoms gets elevated priority. A flag with no symptom connection is more likely to be a borderline statistical deviation.
4
Identify which flag matters most using four criteria
Apply the four-factor framework to your ranked list: magnitude (deviation %), system impact (organ function markers take priority over CBC indices), symptom match, and actionability. The flag that scores highest across all four is where your attention belongs first.
Shortcut: upload your report to FixFirst and get your top priorities ranked automatically — or read the full priority framework.
5
Decide: GP contact, self-directed action, or monitor
Use the urgency tiers above. Significantly abnormal organ markers or results explaining active symptoms: book a GP appointment and bring your ranked priority list. Markers with clear evidence-based self-directed interventions (low ferritin, low vitamin D, low B12): confirm the deficit with a doctor if you haven't already, then act. Borderline flags with no symptoms: note them, re-test at your next routine blood draw.
6
Track your response and re-test
Whether you're supplementing, making dietary changes, or starting a prescribed treatment, the result that told you something is wrong should confirm it's improving. Set a reminder to re-test at 6–12 weeks (supplements) or as directed by your GP (prescribed treatment). An abnormal result that doesn't improve with the expected intervention tells your doctor something the original result couldn't.
Skip the manual calculation
FixFirst reads your actual report, calculates deviation for every flagged marker, looks for clustering patterns, and returns your top priorities in order — so you start at step 4 with the work already done.
Upload your report and get your priority list

Frequently asked questions

What should I do if my blood test results come back abnormal?
Start by checking whether any results carry a critical flag (different colour, exclamation mark, or separate note) — these require same-day medical contact. For standard H/L flags: calculate the percentage deviation for each, match against any symptoms you have, and identify the highest-priority result using magnitude, system impact, symptom match, and actionability. For significantly abnormal results on organ markers, book a GP appointment. For borderline flags with no symptoms, monitor at the next routine test.
Do I need to see a doctor for every abnormal blood test result?
No. Mildly abnormal results on CBC indices (borderline lymphocyte count, slightly low MCV) with no matching symptoms are often worth monitoring at the next blood test rather than requiring a GP appointment. Significantly abnormal organ markers, or any result explaining active symptoms, warrant GP contact. Results with safe, evidence-based self-directed interventions (low ferritin, low vitamin D, low B12) can reasonably be addressed directly, though confirming the result with a GP first is still advisable for significant deviations.
How long can I wait after getting abnormal blood test results?
Critically flagged results: contact your GP or a walk-in clinic the same day. Significantly abnormal results on organ markers (kidney, liver, thyroid): schedule a GP appointment within 1–2 weeks. Mildly abnormal results with no symptoms: monitor at your next routine blood test, typically 3–6 months. The single most important rule: never delay on a critically flagged result — the lab flags these precisely because they require prompt clinical review.
What is a critically abnormal blood test result?
A critically abnormal result is a value so far outside the expected range that it indicates a potentially life-threatening condition requiring immediate intervention. Labs flag these separately from standard H/L tags. If your report has a critical flag, or your GP surgery phones you about a result, contact them that day. Examples include severely low potassium, haemoglobin below 7.0 g/dL, or significantly elevated creatinine indicating acute kidney injury. Standard H and L flags are not critical values; they are common and most do not represent emergencies.
Can abnormal blood test results be a mistake?
Single mild deviations can reflect lab processing variation, collection conditions (prolonged tourniquet time, haemolysis), timing relative to meals or exertion, or natural biological variation. For unexpected mild results, asking your GP about a repeat test in 4–8 weeks is reasonable. Significantly abnormal results on multiple markers from the same system, especially when they match symptoms, are less likely to be artefacts. When in doubt, repeat testing provides more information than anxiety alone.
Medical disclaimer: This guide is for general educational purposes. Critically abnormal results require same-day medical contact. Any result significantly outside the normal range, or any pattern suggesting organ dysfunction, requires evaluation by a licensed healthcare provider.

Get your abnormal results ranked by priority

Upload your blood test report and FixFirst identifies which flags matter most, ranked by magnitude, clustering, and clinical weight, so you know where to start.

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Related guides

Which Flag to Address FirstA four-factor framework for prioritising multiple abnormal results by clinical weight. Multiple Abnormal ResultsWhy 1–3 flags on a 20-marker panel is statistically common and how to read the pattern. Low FerritinOne of the most commonly under-investigated flags — and the root cause of four downstream markers. High TSHWhat elevated TSH means and why it can drive multiple other flags up simultaneously. Analyze My Blood TestUpload any lab report and get a ranked priority list in 30 seconds.