Blood Tests After Surgery
What is normal, what is not, and what the daily numbers actually mean during your recovery.
Why “Abnormal” Often Means “Healing”
Recovering from surgery is itself an “abnormal” state. Your blood test results will not look like a textbook for at least a fortnight - and that is healthy. CRP is meant to be high. Haemoglobin is meant to be low. White cells are meant to climb. Albumin is meant to dip. These are signs that your body is doing what it should.
The skill of post-op care is recognising the difference between an expected pattern and a warning shift. The trend over days matters far more than any single value - which is exactly why your team retests every day until you are stable.
The Timeline of Recovery
| Time after surgery | What is normal | Watch out for |
|---|---|---|
| Day 0 (recovery) | Haemoglobin down 10-20 g/L, white cells 12-15, blood sugar mildly raised. | Sudden fall in BP, fast tachycardia not explained by pain. |
| Day 1-2 | CRP rising rapidly, ileus possible, mild kidney impairment. | Lactate rising, severely low BP, ongoing oozing. |
| Day 3 (CRP peak) | CRP at its highest. Patient feels worst around now even if going to plan. | CRP higher than expected for the operation, new fever spike. |
| Day 4-5 | CRP starts falling 25-50% per day. Appetite returning. Drains coming out. | CRP NOT falling, or a second rise = infection suspicion. |
| Week 1-2 | Platelets climbing above normal (reactive thrombocytosis - healthy). Energy still low. Mild ongoing anaemia. | Persistent fever, wound discharge, calf swelling. |
| 4-6 weeks | Most blood tests back near baseline. Time to recheck iron studies if anaemic. | Persistent anaemia, ongoing fatigue, breathlessness on exertion. |
The 8 Markers Your Team Watches
Full Blood Count (FBC)
Expected pattern: Haemoglobin drops 10-20 g/L after major surgery from blood loss and fluid shifts. White cells normally rise to 12-15 in the first 48 hours - this is the stress response, NOT necessarily infection. Platelets often drop initially then climb above normal at 7-14 days as part of healing.
When to worry: Falling haemoglobin after day 3 suggests ongoing bleeding. White cells staying above 15 past day 4-5 raise infection suspicion. Platelets below 100 are a serious sign and need investigation.
CRP (C-Reactive Protein)
Expected pattern: CRP rises within 6 hours of any surgical trauma. It peaks at 48-72 hours (day 2-3) - often well above 100 mg/L for a major operation. This is the EXPECTED response and does not mean infection.
When to worry: After the day 2-3 peak, CRP should fall steadily by about 25-50% per day. A second rise after day 4-5, or a stubborn plateau, is one of the earliest signs of a surgical site infection or anastomotic leak.
Albumin
Expected pattern: Albumin drops by 5-10 g/L after major surgery. This is partly fluid shifts and partly the liver redirecting protein production toward acute-phase proteins like CRP. Mild low albumin is the rule, not the exception.
When to worry: Albumin below 25 g/L slows wound healing and increases infection risk. Pre-operative low albumin is a much stronger predictor of complications than post-op. Many hospitals now optimise it before surgery.
Kidney Function (eGFR, Creatinine)
Expected pattern: Anaesthesia, dehydration, blood loss and some drugs (NSAIDs, ACE inhibitors, contrast dye) can transiently drop eGFR. A creatinine rise of up to 30% from baseline is expected after major surgery.
When to worry: A 50%+ rise in creatinine, or oliguria (less than 0.5 mL/kg/hour of urine), defines acute kidney injury. Catching it early lets the team adjust fluids and drugs to prevent permanent damage.
Liver Function (ALT, GGT, ALP)
Expected pattern: Mild elevation of liver enzymes is common after anaesthesia and any abdominal surgery - the liver processes the drugs and may be transiently bruised by surgical positioning.
When to worry: A sharp rise in bilirubin or ongoing ALT elevation past day 5 needs evaluation - drug-induced liver injury, biliary leak after gallbladder or bowel surgery, or post-op hepatitis.
Electrolytes (Na, K, Mg)
Expected pattern: Fluid shifts, IV drips and reduced oral intake all push electrolytes around. Sodium and potassium can both go low; magnesium often drops after major surgery.
When to worry: Sodium below 130 mmol/L can cause confusion and seizures. Potassium below 3.0 or above 5.5 risks arrhythmias. These are tested daily in the first 48 hours after major surgery for a reason.
Coagulation (INR, APTT, D-dimer)
Expected pattern: Surgery activates the clotting cascade. D-dimer rises sharply in the first 24-48 hours just from surgical trauma - it is NOT a useful marker for venous thromboembolism in the early post-op period.
When to worry: INR is checked daily on warfarin patients. Heparin or LMWH given for VTE prophylaxis needs monitoring through APTT or anti-Xa levels depending on the agent.
Iron Studies (Ferritin, Iron)
Expected pattern: Ferritin rises sharply after any surgery as it is an acute-phase reactant - so it does NOT reliably measure iron stores for several weeks post-op. Serum iron and transferrin saturation drop transiently regardless of actual iron status.
When to worry: Wait at least 4-6 weeks after major surgery before interpreting iron studies. If anaemia is bothering you, treat empirically with iron rather than chasing numbers that are temporarily skewed.
Different Operations, Different Priorities
| Surgery type | Key markers | Schedule |
|---|---|---|
| Orthopaedic (hip/knee replacement) | FBC for blood loss, D-dimer / clinical assessment for DVT, CRP for prosthesis infection. | Daily FBC for 2-3 days, then on discharge. CRP day 3 and at follow-up. |
| Cardiac (CABG, valve) | Troponin trend, BNP, electrolytes (esp K, Mg), coagulation, FBC. | Multiple times daily in ICU then daily on ward. |
| Abdominal (bowel resection) | CRP trend (anastomotic leak), albumin (healing), electrolytes (ileus), lactate (ischaemia). | Daily until oral intake established and CRP falling. |
| Gynaecological / Obstetric | FBC (blood loss), beta-hCG if relevant, group & save in case of haemorrhage. | On day 1 and as needed. |
| Dental / minor outpatient | Usually none required. Pre-op FBC and coagulation if on blood thinners. | Pre-op only in most cases. |
Post-Op Red Flags - Call Your Team
Questions to Ask Your Surgical Team
What is the trend in my CRP and haemoglobin?
Do my electrolytes look stable on the current IV fluids?
How is my kidney function compared to before surgery?
Am I at high enough risk to need ongoing VTE prophylaxis after discharge?
When should I have follow-up bloods checked at my GP?
What numbers would prompt me to come back to ED?
Track Your Recovery Trends
Upload your hospital and follow-up blood tests to SmarterBlood - we chart each marker over your recovery so you can see whether things are heading back to baseline.