Abnormal Blood Test Results
Do not panic - most abnormal results are mild and manageable. This guide explains what high and low values mean for 25+ common markers, when to worry, and what to ask your doctor.
Understanding the Severity Scale
Not all abnormal results are created equal. A result that is 1% outside the reference range is very different from one that is 50% outside it. Here is how to think about severity.
Your result falls within the laboratory reference range. No action typically required.
Just outside the reference range. Often monitored with repeat testing in a few months.
Clearly outside normal but not immediately dangerous. Investigation and lifestyle changes often recommended.
Significantly outside normal. Usually requires medical intervention and follow-up testing.
Dangerously abnormal. The lab will often call your doctor directly. May require urgent treatment.
What 25+ Markers Mean When Abnormal
Below is a comprehensive reference for the most commonly tested blood markers. For each marker, you will find what high and low values typically indicate, the most common causes, and how urgently the result should be reviewed.
Blood Count (FBC)
Haemoglobin (Hb)
HIGH means:
Dehydration, polycythaemia, chronic lung disease, living at high altitude. Smoking can chronically elevate Hb.
LOW means:
Iron deficiency anaemia, chronic disease, blood loss (menstrual, GI), B12/folate deficiency, kidney disease.
Most common cause: Most commonly iron deficiency (women) or chronic disease (elderly)
White Blood Cells (WBC)
HIGH means:
Bacterial infection, inflammation, stress response, corticosteroid medications, smoking, rarely leukaemia.
LOW means:
Viral infection, autoimmune conditions, bone marrow disorders, chemotherapy, some medications.
Most common cause: Infection is the most common cause in both directions
Platelets (PLT)
HIGH means:
Iron deficiency, inflammation, infection, post-surgery, rarely myeloproliferative disorders.
LOW means:
Viral infections, liver disease, autoimmune destruction (ITP), medications (heparin), alcohol excess.
Most common cause: Reactive thrombocytosis (iron deficiency, infection) is far more common than primary causes
Metabolic / Electrolytes
Sodium (Na)
HIGH means:
Dehydration, diabetes insipidus, excessive salt intake, certain medications.
LOW means:
Diuretics, heart failure, kidney disease, excessive water intake, SIADH, vomiting/diarrhoea.
Most common cause: Diuretics and dehydration are the most common causes
Potassium (K)
HIGH means:
Kidney disease, ACE inhibitors/ARBs, potassium supplements, haemolysed sample (false high).
LOW means:
Diuretics, vomiting/diarrhoea, excessive sweating, low dietary intake, insulin use.
Most common cause: Medications (diuretics, ACE inhibitors) are the most common cause
Creatinine
HIGH means:
Kidney impairment, dehydration, high protein diet, intense exercise, large muscle mass.
LOW means:
Low muscle mass, malnutrition, liver disease. Low creatinine is rarely clinically significant.
Most common cause: Dehydration and medications are common reversible causes
eGFR
HIGH means:
Not clinically relevant (higher is better for kidney function).
LOW means:
Chronic kidney disease (staged by eGFR), acute kidney injury, dehydration, age-related decline.
Most common cause: Mild reduction is common with age; significant drops need investigation
Calcium (Ca)
HIGH means:
Hyperparathyroidism, vitamin D excess, cancer, thiazide diuretics, immobilisation.
LOW means:
Vitamin D deficiency, hypoparathyroidism, kidney disease, low albumin (which gives a falsely low reading).
Most common cause: Primary hyperparathyroidism (high) and vitamin D deficiency (low) are most common
Liver Function
ALT
HIGH means:
Fatty liver disease (NAFLD), hepatitis, alcohol, medications (statins, paracetamol), obesity.
LOW means:
Not clinically significant. Very low ALT is normal.
Most common cause: Fatty liver disease is now the most common cause of elevated ALT in Australia
AST
HIGH means:
Liver disease, heart damage (myocardial infarction), muscle injury, alcohol, medications.
LOW means:
Not clinically significant.
Most common cause: Often elevated alongside ALT in liver disease; isolated AST elevation may suggest muscle or cardiac source
GGT
HIGH means:
Alcohol use, fatty liver, bile duct obstruction, medications, pancreatic disease.
LOW means:
Not clinically significant.
Most common cause: Very sensitive to alcohol - even moderate drinking can elevate GGT
Bilirubin
HIGH means:
Gilbert syndrome (benign, affects 5-10% of population), liver disease, bile duct obstruction, haemolysis.
LOW means:
Not clinically significant.
Most common cause: Mildly elevated bilirubin in an otherwise healthy person is usually Gilbert syndrome
Thyroid Function
TSH
HIGH means:
Underactive thyroid (hypothyroidism), Hashimoto's thyroiditis, iodine deficiency, recovering from illness.
LOW means:
Overactive thyroid (hyperthyroidism), Graves' disease, thyroid nodules, excessive thyroid medication, early pregnancy.
Most common cause: Hashimoto's thyroiditis (high TSH) and Graves' disease (low TSH) are the most common autoimmune causes
Free T4
HIGH means:
Hyperthyroidism, excessive thyroid medication, early thyroiditis (hormone leaking from damaged gland).
LOW means:
Hypothyroidism, pituitary disease, severe illness (sick euthyroid syndrome), iodine deficiency.
Most common cause: Interpreted together with TSH - the combination tells the full story
Lipids (Cholesterol)
Total Cholesterol
HIGH means:
Diet, genetics (familial hypercholesterolaemia), hypothyroidism, kidney disease, diabetes.
LOW means:
Malnutrition, liver disease, hyperthyroidism, some medications. Very low cholesterol is uncommon.
Most common cause: Combination of diet, genetics, and age is the most common explanation
LDL Cholesterol
HIGH means:
Diet high in saturated fat, genetics, hypothyroidism, diabetes, obesity.
LOW means:
Statins (intentionally), hyperthyroidism, malabsorption. Low LDL is generally favourable.
Most common cause: Primary target for cardiovascular risk reduction
HDL Cholesterol
HIGH means:
Regular exercise, moderate alcohol intake, genetics. High HDL is protective.
LOW means:
Smoking, sedentary lifestyle, metabolic syndrome, obesity, type 2 diabetes.
Most common cause: Low HDL is a key component of metabolic syndrome
Triglycerides
HIGH means:
Alcohol, obesity, diabetes, non-fasting sample, high-sugar diet, medications, kidney disease.
LOW means:
Malnutrition, hyperthyroidism, malabsorption. Low triglycerides are rarely a concern.
Most common cause: Non-fasting sample is the most common cause of unexpectedly high triglycerides
Diabetes, Vitamins & Others
HbA1c
HIGH means:
Diabetes (>6.5%), pre-diabetes (5.7-6.4%), insulin resistance, polycystic ovary syndrome.
LOW means:
Not typically a concern. Can be falsely low with haemolytic anaemia or recent blood transfusion.
Most common cause: The primary screening and monitoring test for diabetes
Fasting Glucose
HIGH means:
Diabetes, pre-diabetes, stress response (cortisol), medications (corticosteroids), non-fasting sample.
LOW means:
Insulin excess (medication or tumour), liver disease, alcohol, prolonged fasting, adrenal insufficiency.
Most common cause: Pre-diabetes is extremely common and often the first warning sign
Ferritin
HIGH means:
Iron overload (haemochromatosis), inflammation (acute phase reactant), liver disease, alcohol, infection.
LOW means:
Iron deficiency (most common nutritional deficiency worldwide), blood loss, pregnancy, vegetarian diet.
Most common cause: Low ferritin in menstruating women is extremely common and often causes fatigue
CRP
HIGH means:
Infection, inflammation, autoimmune disease, tissue injury, obesity, smoking.
LOW means:
Not clinically significant. Low CRP is normal and desirable.
Most common cause: Non-specific - rises with any inflammatory process. Very high CRP (>100) suggests serious infection.
Vitamin D
HIGH means:
Excessive supplementation (toxicity is rare but possible), granulomatous diseases.
LOW means:
Insufficient sun exposure, dark skin, obesity, malabsorption, kidney disease, older age.
Most common cause: Over 30% of Australian adults are vitamin D deficient despite abundant sunshine
Vitamin B12
HIGH means:
Liver disease, myeloproliferative disorders, excessive supplementation. High B12 is usually harmless.
LOW means:
Pernicious anaemia, vegetarian/vegan diet, metformin use, malabsorption, gastric surgery, older age.
Most common cause: Dietary insufficiency (vegans) and pernicious anaemia (autoimmune) are most common
Uric Acid
HIGH means:
Gout, kidney disease, high-purine diet (red meat, shellfish, alcohol), medications (diuretics), obesity.
LOW means:
Liver disease, Fanconi syndrome, medications (allopurinol - intentionally). Low uric acid is rarely a concern.
Most common cause: Not everyone with high uric acid gets gout, but all gout patients have high uric acid at some point
When Your Doctor Calls
How your results are communicated often tells you more about urgency than the actual numbers. Here is what different callback methods typically mean.
Letter or online portal
Results are normal or have minor findings that do not require immediate action. Your doctor has reviewed them and is not concerned. You may be asked to discuss at your next routine appointment.
Receptionist calls to book follow-up
Something needs discussion but is not urgent. Common for borderline results, mildly abnormal findings, or results that need repeat testing. Do not panic - this is standard practice.
Doctor calls you personally
Something is significantly abnormal and needs attention. Your doctor wants to discuss the results, plan treatment, or order urgent follow-up tests. This warrants prompt attention but is usually manageable.
"Come in today" or "Go to emergency"
A critical result that needs immediate medical intervention. Very rare, but possible for dangerously high potassium, very low haemoglobin, or critically abnormal results that pose immediate risk.
Why Results Change Between Tests
It is common to see different results from one test to the next, even when nothing significant has changed with your health. Understanding why helps you worry less about minor fluctuations.
Biological Variation
Your body is not a machine. Cholesterol can vary by 10-15% between tests, haemoglobin by up to 10 g/L, and white blood cells by 20-30%. These are normal fluctuations and not a sign that something has changed.
Fasting Status
Eating before a fasting blood test can raise triglycerides by 20-30% and glucose by 1-2 mmol/L. If you accidentally ate, tell your doctor rather than worrying about the high result.
Time of Day
Cortisol peaks in the morning and falls at night. Iron is highest in the morning. Testosterone peaks at 8am. The time your blood was drawn can significantly affect certain results.
Medications
Statins raise ALT/AST, diuretics affect electrolytes, metformin lowers B12, corticosteroids raise glucose and WBC, biotin supplements interfere with thyroid tests. Always list your medications when discussing results.
Recent Illness or Exercise
A cold or flu can elevate WBC and CRP for weeks. Intense exercise within 24 hours can raise CK, AST, and potassium. Even the stress of a difficult blood draw can raise cortisol and glucose.
Hydration
Being dehydrated concentrates your blood, making haemoglobin, haematocrit, sodium, and protein appear falsely high. Drinking plenty of water before your test helps ensure accurate results.
10 Questions to Ask Your Doctor About Abnormal Results
Walking into your appointment with prepared questions ensures you leave with answers. Here are 10 ready-to-use questions that will help you understand your results and next steps.
Which of my results are you most concerned about, and why?
Is this result likely a one-off fluctuation, or does it fit a pattern?
Do I need to repeat this test, and if so, when?
Could any of my medications be causing this abnormal result?
What is the most likely explanation for this result in my case?
At what point would this result become something to worry about?
Are there lifestyle changes that could improve this marker?
Do I need any additional tests to investigate further?
How does this result compare to my previous tests?
Should I see a specialist about this, or can we manage it in general practice?
Frequently Asked Questions
Your doctor is almost certainly right. Doctors interpret results in clinical context - your symptoms, medical history, medications, age, sex, and the degree of abnormality all matter. A mildly elevated GGT in someone who had a few drinks over the weekend is expected and trivial. The H/L flags on reports are purely mathematical (outside the statistical reference range) and do not reflect clinical significance. If your doctor says "fine," it means the results are not concerning in your specific clinical context. If you are still worried, ask your doctor to explain which results they are monitoring and why they are not concerned.
Yes, both acute and chronic stress affect blood tests. Acute stress (panic attack, severe anxiety before the test) triggers cortisol and adrenaline release, which can raise blood glucose by 1-3 mmol/L, increase white blood cell count by 20-40%, and elevate cholesterol. Chronic stress over weeks or months can suppress thyroid function, raise inflammatory markers like CRP, impair immune function (lowering lymphocytes), and disrupt blood sugar regulation. If you were particularly stressed, anxious, or had a panic attack shortly before your blood test, let your doctor know so they can factor this in.
For mildly abnormal results, your doctor will typically recommend repeating the test in 4-12 weeks to distinguish a one-off fluctuation from a persistent finding. Borderline results are especially likely to normalise on repeat testing. For significantly abnormal results, your doctor may order additional tests immediately rather than waiting to repeat the same one. For critical results (very high potassium, very low haemoglobin), the lab usually alerts your doctor directly and repeat testing is done urgently, sometimes the same day.
The consequences depend entirely on which marker is abnormal and by how much. Mildly low vitamin D is extremely common and not urgent - though fixing it improves energy and bone health. Slightly elevated cholesterol has no immediate symptoms but increases cardiovascular risk over decades. However, significantly abnormal potassium or calcium can cause dangerous heart rhythm problems if left untreated. Very low haemoglobin can cause organ damage. Undiagnosed diabetes causes slow, progressive damage to kidneys, eyes, and nerves. The safest approach is always to discuss any abnormal results with your doctor, even if you feel perfectly fine.
For some markers, diet makes a significant difference. Iron deficiency responds to iron-rich foods (red meat, spinach, lentils) combined with vitamin C for absorption. High cholesterol often improves with reduced saturated fat and increased fibre. High triglycerides respond dramatically to reducing alcohol and refined sugars. Elevated HbA1c and fasting glucose can be reversed in early stages through diet, exercise, and weight loss. Vitamin D deficiency responds to safe sun exposure and supplementation. However, some abnormalities require medical treatment beyond diet: thyroid dysfunction needs hormone replacement, significant kidney disease needs specialist management, and genetic conditions like familial hypercholesterolaemia often need statins regardless of diet.
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