Blood Tests for Easy Bruising and Unexplained Bleeding
Bruising from the lightest bump? Bleeding that won't stop? Your blood holds the answers. Here are the tests that explain why — and when to worry.
When Bruising Is More Than Just Clumsy
Everyone bruises occasionally — it's a normal part of being human. But there is a significant difference between “I walked into the coffee table” and “I woke up with bruises I can't explain.” The key question is not whether you bruise, but whether your bruising has changed.
Easy bruising is one of the most common reasons Australians ask their GP for blood tests. The good news is that most cases have a straightforward, treatable explanation. A standard blood panel can check for the most common causes in one visit.
Below is a practical guide to distinguishing normal bruising from bruising that deserves investigation.
Normal vs Concerning Bruising
Use this comparison to decide whether your bruising pattern warrants a blood test. If you recognise yourself in the “concerning” column for two or more aspects, book a GP appointment.
| Aspect | Probably Normal | Worth Investigating |
|---|---|---|
| Location | Shins, forearms, thighs (bony or exposed areas) | Trunk, back, face, or places you didn't bump |
| Size | Small to moderate (coin-sized), matches the bump | Large bruises from minor contact, or bruises that spread |
| Frequency | Occasional, and you remember hitting something | Multiple bruises appearing with no recalled injury |
| Healing | Goes through colour changes (purple > green > yellow) over 2-3 weeks | Takes more than 4 weeks to heal, or new ones appear before old ones fade |
| Accompanying signs | Bruise only, no other symptoms | Also bleeding gums, nosebleeds, heavy periods, or blood in urine/stool |
| Age factor | Skin bruises more easily over 60 (senile purpura) — cosmetic, not dangerous | New onset at any age with no explanation, especially if rapid |
7 Causes of Easy Bruising Your Blood Can Reveal
Each of these conditions affects a different part of your body's clotting system. Understanding which part is failing is the key to finding the right treatment.
Low Platelets (Thrombocytopenia)
How it causes bruising: Platelets are tiny cell fragments that form the initial plug when a blood vessel is damaged. A normal count is 150-400 x10^9/L. Below 100, you bruise more easily. Below 50, spontaneous bruising occurs. Below 20 is a medical emergency — you can bleed internally without any trauma.
The clue to look for: Petechiae — tiny red-purple dots (like a rash) that don’t blanch when pressed. These pinpoint dots are the hallmark of low platelets, distinct from regular bruising. They often appear on the lower legs first.
Liver Disease
How it causes bruising: Your liver manufactures nearly all of your clotting factors (the proteins that form a stable blood clot). When the liver is damaged — by alcohol, fatty liver disease, hepatitis, or other conditions — it cannot produce enough clotting factors. The liver also clears old platelets and makes thrombopoietin, the hormone that stimulates platelet production.
The clue to look for: Bruising plus any of these: yellowish skin or eyes (jaundice), spider naevi (small red spider-web marks on chest/face), swollen abdomen, dark urine, or pale stools. Alcohol use, obesity, or hepatitis risk factors make liver disease more likely.
Vitamin K Deficiency
How it causes bruising: Vitamin K is essential for producing clotting factors II, VII, IX, and X in the liver. Without adequate vitamin K, your blood takes longer to clot even though your liver is healthy. Vitamin K comes from green leafy vegetables and gut bacteria. Deficiency is uncommon in healthy adults but happens with malabsorption conditions (coeliac, Crohn’s), prolonged antibiotic use (kills gut bacteria), or very restricted diets.
The clue to look for: A prolonged PT/INR (prothrombin time) with NORMAL liver function tests is the classic pattern. If your LFTs are fine but your blood takes too long to clot, vitamin K deficiency is the prime suspect.
Vitamin C Deficiency (Scurvy)
How it causes bruising: Vitamin C is essential for producing collagen — the protein that forms the structural walls of blood vessels. Without it, capillaries become fragile and leak blood into surrounding tissues. Scurvy is rare but not extinct — it still occurs in Australia, particularly among elderly people living alone, people with very restricted diets, smokers (who need 35mg more vitamin C daily), and those with eating disorders.
The clue to look for: Distinctive bruising pattern: perifollicular haemorrhage (bruising around hair follicles giving a speckled rash). Also: swollen bleeding gums, loose teeth, corkscrew-shaped body hair, slow wound healing. The bruises often appear on the legs and buttocks first.
Clotting Factor Disorders
How it causes bruising: Your blood has 13 clotting factors that work in a precise cascade to form a stable clot. If any factor is deficient or dysfunctional — due to inherited conditions (haemophilia, von Willebrand disease) or acquired disorders — clotting fails. Von Willebrand disease is the most common inherited bleeding disorder, affecting up to 1% of Australians, though most have a mild form.
The clue to look for: Bleeding that is disproportionate to the injury. Nosebleeds lasting more than 20 minutes. Heavy menstrual bleeding (soaking through a pad every hour). Prolonged bleeding after dental work or minor surgery. Family history of bleeding problems.
Kidney Dysfunction
How it causes bruising: Advanced kidney disease causes uraemia — a build-up of waste products in the blood that impairs platelet function. Your platelet count may be normal, but the platelets don’t work properly. Uraemic toxins interfere with the platelet’s ability to stick together and form a plug. This is called qualitative platelet dysfunction.
The clue to look for: Bruising or prolonged bleeding with NORMAL platelet count but elevated creatinine and low eGFR. This is a subtle finding — the standard clotting tests (PT, APTT) may also be normal because the problem is platelet function, not the clotting cascade.
Iron Deficiency & Anaemia
How it causes bruising: Iron deficiency itself doesn’t directly cause bruising, but the two conditions frequently coexist and share a common root cause. Heavy menstrual bleeding both depletes iron stores AND suggests an underlying bleeding tendency. Additionally, severe iron deficiency can mildly impair platelet function. If you bruise easily AND are iron deficient, the question becomes: what is causing you to lose blood?
The clue to look for: The connection to look for: low ferritin alongside easy bruising may mean you are losing blood somewhere (heavy periods, GI tract). This combination warrants further investigation rather than just treating the iron deficiency.
The Bruising Blood Panel
This is the standard set of blood tests your GP should order to investigate easy bruising or unexplained bleeding. Most are bulk billed in Australia when clinically indicated.
| Test | What It Checks | Cost (Australia) |
|---|---|---|
| Full Blood Count (FBC) | Platelet count, haemoglobin, white cells | Bulk billed |
| Blood Film (Peripheral Smear) | Platelet size and shape under microscope | Bulk billed |
| PT/INR (Prothrombin Time) | Extrinsic clotting pathway — liver function, vitamin K | Bulk billed |
| APTT (Activated Partial Thromboplastin Time) | Intrinsic clotting pathway — clotting factor disorders | Bulk billed |
| Fibrinogen | The final clotting protein — low levels impair clot stability | Bulk billed |
| Liver Function Tests (LFTs) | ALT, AST, GGT, Bilirubin, Albumin | Bulk billed |
| Iron Studies (Ferritin, Fe, TIBC) | Iron deficiency — often coexists with bleeding | Bulk billed |
| Kidney Function (eGFR, Creatinine) | Uraemia impairs platelet function | Bulk billed |
| Vitamin C Level | Scurvy — rare but real | May have gap |
| Von Willebrand Factor Panel | Most common inherited bleeding disorder | Bulk billed |
Medications That Increase Bruising
Before assuming a blood disorder, check your medicine cabinet. These common medications are the single most frequent cause of increased bruising — and they are not a blood test finding. Never stop a prescribed medication without speaking to your doctor first.
Aspirin
Low-dose aspirin (100mg daily)
How: Permanently disables platelet function for the platelet's entire 10-day lifespan
Action: NEVER stop without discussing with your doctor — the heart protection usually outweighs bruising
NSAIDs
Ibuprofen (Nurofen), naproxen, diclofenac
How: Temporarily impairs platelet function and can damage the stomach lining
Action: Consider paracetamol instead, or take with food. Discuss alternatives with your pharmacist
Blood thinners
Warfarin, rivaroxaban (Xarelto), apixaban (Eliquis)
How: Deliberately reduce clotting ability — bruising is an expected side effect
Action: Warfarin: regular INR monitoring. DOACs: report excessive bruising to your doctor
Corticosteroids
Prednisolone, cortisone (long-term use)
How: Thin the skin and weaken blood vessel walls over time
Action: Don't stop abruptly. Discuss skin protection strategies with your doctor
Antidepressants (SSRIs)
Sertraline, fluoxetine, citalopram
How: Block serotonin uptake by platelets, mildly impairing platelet clumping
Action: Usually mild effect. Mention if bruising is bothersome at your next review
Fish oil supplements
Omega-3 fatty acids (high dose)
How: At doses above 3g/day, can mildly reduce platelet aggregation
Action: Mention all supplements to your doctor before blood tests or surgery
What to Ask Your Doctor
When you see your GP about bruising, preparation makes a big difference. Here is a ready-to-use script that covers the information your doctor needs.
“I've noticed I'm bruising much more easily than usual. The bruises appear [on my arms/legs/trunk/all over] and I [can/cannot] remember bumping into things. This has been happening for about [timeframe]. I also [have/do not have] nosebleeds, bleeding gums, or heavy periods. I take these medications: [list all medications and supplements including fish oil]. Could we run a full blood count with coagulation studies and liver function tests?”
Bring to your appointment:
Photos of your bruises (especially ones that appeared without injury)
A complete list of ALL medications and supplements (including over-the-counter)
Family history of bleeding disorders (if any relatives bruise easily or had excessive surgical bleeding)
Notes on any other bleeding symptoms: gum bleeding, heavy periods, blood in urine or stool
Urgent Signs: When to Seek Immediate Help
Most bruising is not an emergency. However, certain signs indicate a potentially serious condition that needs prompt medical attention. Go to the emergency department or call 000 if you notice:
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