Blood Tests for Chronic Pain
When pain persists without a clear injury, blood tests can reveal treatable causes - from hidden inflammation and vitamin deficiencies to autoimmune conditions and nerve damage.
When Pain Has a Blood-Testable Cause
Chronic pain - defined as pain lasting more than three months - affects an estimated 3.4 million Australians. While some chronic pain is primarily neurological (the pain system itself malfunctioning), a significant proportion has an identifiable biochemical cause that shows up on blood tests. Studies suggest that 30-40% of patients referred to chronic pain clinics have at least one treatable abnormality on routine blood work.
The challenge is that many of these causes produce overlapping symptoms. Fatigue, widespread aching, and poor sleep are common to vitamin D deficiency, hypothyroidism, iron deficiency, and fibromyalgia. Without blood tests, it is impossible to distinguish them clinically. A comprehensive pain-focused blood panel can identify (or rule out) these causes in a single pathology visit.
Key insight: Even when chronic pain is ultimately diagnosed as fibromyalgia or central sensitisation, blood tests are essential to rule out conditions that mimic it. Treating vitamin D deficiency, hypothyroidism, or B12 deficiency can dramatically reduce pain - and these are conditions that will never improve with pain medications alone.
Inflammatory vs Neuropathic vs Musculoskeletal Pain
Chronic pain is not one condition - it is a symptom with many possible causes. Identifying the pain type helps your doctor order the right blood tests first time. Here are the three major categories and the blood tests most relevant to each.
Inflammatory Pain
Caused by an overactive immune response attacking your own tissues. Often worse in the morning, improves with movement, and is accompanied by swelling, warmth, or redness.
Common conditions: Rheumatoid arthritis, lupus, polymyalgia rheumatica, ankylosing spondylitis, inflammatory bowel disease, vasculitis
Neuropathic Pain
Caused by nerve damage or dysfunction. Feels like burning, tingling, electric shocks, or numbness. Often described as pain that is out of proportion to any visible cause.
Common conditions: Diabetic neuropathy, B12 deficiency neuropathy, post-herpetic neuralgia, small fibre neuropathy, carpal tunnel syndrome
Musculoskeletal Pain
Originates from bones, muscles, tendons, or ligaments. Can be localised or widespread. Often worsened by specific movements or positions and may involve stiffness.
Common conditions: Fibromyalgia, osteomalacia (vitamin D deficiency), hypothyroid myopathy, iron deficiency myalgia, magnesium deficiency cramps
10 Blood Tests That Can Explain Chronic Pain
CRP & ESR (Inflammation Markers)
The Pain Connection
Systemic inflammation is one of the most common treatable causes of chronic widespread pain. When inflammation is present, pain signals are amplified throughout the nervous system - a phenomenon called central sensitisation. Even mild chronic inflammation (CRP 3-10 mg/L) can maintain pain states that otherwise seem unexplainable.
What It Reveals
CRP rises within hours of inflammatory activity and is the best acute-phase marker. ESR moves more slowly (days to weeks) and reflects chronic inflammation trends. Together, they distinguish inflammatory pain from mechanical or neuropathic pain. In fibromyalgia, CRP and ESR are typically normal - this is actually a useful diagnostic finding because it helps rule out autoimmune and inflammatory conditions.
Clinical detail: Normal CRP is below 5 mg/L. In active rheumatoid arthritis, CRP can reach 20-100+ mg/L. In polymyalgia rheumatica (a condition causing severe shoulder and hip pain in people over 50), ESR is often dramatically elevated above 50 mm/hr. The combination of widespread pain with normal CRP and ESR points toward fibromyalgia, vitamin D deficiency, or hypothyroidism rather than autoimmune disease.
Vitamin D (25-Hydroxyvitamin D)
The Pain Connection
Vitamin D deficiency is one of the most under-diagnosed causes of chronic musculoskeletal pain. It directly causes osteomalacia (soft bones) in adults, which produces deep bone pain, muscle weakness, and widespread aching that is often misdiagnosed as fibromyalgia. Studies show that 26-71% of chronic pain patients are vitamin D deficient, compared to 20-30% of the general population.
What It Reveals
A level below 50 nmol/L is deficient. Below 25 nmol/L is severely deficient and almost always symptomatic. When vitamin D drops low enough, the body pulls calcium from bones via PTH (parathyroid hormone), causing bone pain, fractures, and muscle weakness. Checking vitamin D alongside calcium and PTH reveals whether bone metabolism has been affected.
Clinical detail: In Australia, vitamin D deficiency is most common during winter months in southern states, in people who cover their skin, work indoors, or have darker skin. The pain pattern of osteomalacia is characteristically diffuse - affecting ribs, pelvis, shins, and thighs rather than joints. A trial of vitamin D supplementation (1000-4000 IU daily for 8-12 weeks) often produces dramatic pain improvement if deficiency was the cause.
Vitamin B12 & Folate
The Pain Connection
B12 deficiency causes peripheral neuropathy - nerve damage that produces burning pain, tingling, and numbness, typically starting in the feet and progressing upward. The pain is neuropathic in character: burning, electric, or pins-and-needles rather than aching. B12 deficiency neuropathy is often mistaken for diabetic neuropathy or idiopathic small fibre neuropathy.
What It Reveals
Serum B12 below 200 pmol/L is deficient. However, functional B12 deficiency can occur at levels up to 300 pmol/L - this is the "grey zone" where symptoms can appear despite a technically normal result. Methylmalonic acid (MMA) is a more sensitive test: if MMA is elevated while B12 is in the grey zone, functional deficiency is confirmed.
Clinical detail: B12 deficiency is common in vegans and vegetarians (no dietary B12 from plants), people over 60 (reduced stomach acid impairs absorption), those taking metformin or proton pump inhibitors (omeprazole, pantoprazole), and people with pernicious anaemia (autoimmune destruction of intrinsic factor). If caught early, B12 supplementation can reverse neuropathic pain. If nerve damage has been present for years, recovery may be incomplete.
Iron Studies (Ferritin, Serum Iron, Transferrin)
The Pain Connection
Iron deficiency is associated with widespread muscular aching, exercise intolerance, restless legs syndrome, and fatigue-related pain amplification. Low iron reduces oxygen delivery to muscles and tissues, causing a dull, persistent aching that worsens with activity. Restless legs syndrome - an irresistible urge to move the legs accompanied by uncomfortable sensations - is strongly linked to ferritin below 50 ug/L.
What It Reveals
Ferritin below 30 ug/L indicates iron depletion. Below 15 ug/L is frank deficiency. However, ferritin is also an acute-phase reactant - it rises with inflammation, infection, and liver disease. A person can be iron deficient with a "normal" ferritin if they also have concurrent inflammation. Checking transferrin saturation alongside ferritin catches these masked deficiencies.
Clinical detail: Iron deficiency without anaemia (low ferritin, normal haemoglobin) is extremely common in women of reproductive age, affecting up to 20% of Australian women. It causes symptoms including fatigue, muscle aching, poor concentration, and exercise intolerance well before haemoglobin drops. Many GPs only check haemoglobin and miss isolated ferritin depletion. Always ask for full iron studies, not just an FBC.
Thyroid Function (TSH, Free T4, Free T3)
The Pain Connection
Hypothyroidism (underactive thyroid) causes a characteristic myopathy - muscle pain, stiffness, and weakness that is often widespread and poorly localised. Patients describe feeling like they have the flu all the time. Thyroid-related pain typically involves the large muscle groups: thighs, shoulders, and upper arms. It is often accompanied by fatigue, weight gain, constipation, and cold intolerance.
What It Reveals
TSH above 4.0-5.0 mIU/L suggests hypothyroidism. Subclinical hypothyroidism (TSH 4-10 with normal Free T4) can cause pain symptoms even though it is technically "mild". Free T4 below the reference range confirms overt hypothyroidism. Thyroid antibodies (anti-TPO) identify Hashimoto’s thyroiditis, the most common cause of hypothyroidism in Australia.
Clinical detail: Hashimoto’s thyroiditis affects 5-10% of women and is often diagnosed in the 30-50 age range - the same demographic frequently diagnosed with fibromyalgia. Studies suggest that up to 30% of fibromyalgia patients have undiagnosed thyroid dysfunction when subclinical hypothyroidism is included. A trial of thyroid replacement may dramatically improve pain in this subset.
Uric Acid
The Pain Connection
Elevated uric acid causes gout - intensely painful joint inflammation, classically affecting the big toe but also the ankles, knees, wrists, and elbows. Chronic gout can produce persistent pain between acute flares, with uric acid crystals depositing in joints (tophi) and causing ongoing low-grade inflammation. Gout is the most common inflammatory arthritis in men over 40.
What It Reveals
Uric acid above 0.42 mmol/L (7.0 mg/dL) increases crystallisation risk. However, uric acid can paradoxically drop during an acute gout flare (crystals are depositing, removing uric acid from blood). For accurate results, test during a pain-free period. Kidney function (eGFR, creatinine) should always be tested alongside uric acid because impaired kidneys reduce uric acid excretion.
Clinical detail: In Australia, gout prevalence has doubled in the last 20 years, driven by obesity, metabolic syndrome, and increased fructose consumption. Two-thirds of body uric acid comes from internal metabolism, not diet. Most gout patients under-excrete uric acid through their kidneys rather than over-producing it. Allopurinol (the main preventive medication) targets a uric acid level below 0.36 mmol/L to dissolve existing crystals.
Rheumatoid Factor & ANA (Autoimmune Markers)
The Pain Connection
Autoimmune conditions are a major cause of chronic pain that often takes years to diagnose. The average time from symptom onset to autoimmune diagnosis is 4-5 years. Autoimmune pain tends to be symmetrical (both sides equally), associated with morning stiffness lasting more than 30 minutes, and accompanied by fatigue and sometimes low-grade fevers.
What It Reveals
Rheumatoid Factor (RF) is positive in about 70% of RA patients but is not specific - it also appears in chronic infections, liver disease, and 5-10% of healthy people. Anti-CCP is far more specific for RA and can be positive years before symptoms. ANA is positive in most lupus patients but also in many people without autoimmune disease (10-15% of healthy women have a low-positive ANA).
Clinical detail: A positive ANA alone is not a diagnosis. The pattern and titre matter: homogeneous pattern at 1:320+ is more concerning than speckled at 1:80. If ANA is positive with joint pain PLUS skin rash, mouth ulcers, hair loss, or Raynaud’s phenomenon, lupus should be investigated with anti-dsDNA, complement levels, and a urinalysis. Negative ANA essentially rules out lupus (97% sensitivity).
HbA1c & Fasting Glucose (Diabetic Neuropathy)
The Pain Connection
Diabetic neuropathy is the most common cause of peripheral neuropathy worldwide. High blood sugar damages small blood vessels that supply nerves, causing progressive burning pain, numbness, and tingling in the feet and hands. Crucially, prediabetes (HbA1c 5.7-6.4%) can also cause neuropathy - up to 30% of "idiopathic" neuropathy patients have undiagnosed prediabetes.
What It Reveals
HbA1c reflects average blood sugar over 3 months. Below 5.7% is normal. 5.7-6.4% is prediabetes. 6.5% or above is diabetes. Fasting glucose above 5.5 mmol/L is prediabetes, above 7.0 is diabetes. Adding fasting insulin can detect insulin resistance (hyperinsulinaemia) even when glucose is still normal - the earliest detectable stage.
Clinical detail: In people with unexplained burning foot pain, HbA1c should always be checked even if they have no known diabetes risk factors. Early detection of prediabetes allows intervention (weight loss, exercise, dietary changes) that can halt or reverse neuropathy progression. Once nerves are severely damaged, recovery is limited even with perfect glucose control.
Calcium & Magnesium
The Pain Connection
Calcium and magnesium are essential for normal muscle contraction and nerve function. Low calcium causes muscle cramps, spasms, and perioral tingling (tetany). Low magnesium causes muscle cramps, fasciculations (twitching), widespread aching, and fatigue. Magnesium deficiency is particularly common (estimated 10-30% of Australians) and is easily missed because standard blood tests only measure serum magnesium, which represents just 1% of total body magnesium.
What It Reveals
Corrected calcium below 2.15 mmol/L is low. Magnesium below 0.70 mmol/L is deficient. However, serum magnesium can be normal even with significant tissue depletion. If symptoms suggest magnesium deficiency (cramps, twitching, fatigue, pain) but serum magnesium is normal, a therapeutic trial of magnesium supplementation (400 mg/day for 4-6 weeks) is reasonable.
Clinical detail: Medications that deplete magnesium include proton pump inhibitors (omeprazole, pantoprazole), loop diuretics (furosemide), and excessive alcohol. High calcium (hypercalcaemia) causes its own pain syndrome: bone pain, abdominal pain, and muscle weakness - typically from hyperparathyroidism or malignancy. Always check PTH if calcium is elevated.
Full Blood Count (FBC)
The Pain Connection
An FBC is often overlooked in chronic pain investigations, but it provides crucial information. Anaemia (low haemoglobin) of any cause amplifies pain perception through reduced tissue oxygenation. An elevated white cell count can point toward hidden infection or inflammation. Macrocytosis (high MCV) suggests B12 or folate deficiency even before levels drop below the reference range.
What It Reveals
Low haemoglobin with low MCV suggests iron deficiency. Low haemoglobin with high MCV suggests B12 or folate deficiency. An elevated white cell count with chronic pain may indicate an occult infection, autoimmune flare, or rarely a haematological malignancy. Thrombocytosis (high platelets) is often reactive to chronic inflammation.
Clinical detail: The FBC is inexpensive, always bulk billed in Australia, and provides a broad screening overview. It is the starting point for any chronic pain blood workup. A completely normal FBC with normal CRP/ESR significantly narrows the differential diagnosis and helps focus further testing on deficiency states (vitamin D, B12) and metabolic causes (thyroid, blood sugar).
The Chronic Pain Blood Panel
This table summarises all recommended tests, grouped by priority. "Essential" tests should be included in every chronic pain workup. "Recommended" tests add useful diagnostic information. "If indicated" tests are ordered when clinical features suggest a specific condition.
| Test | What It Checks | Pain Type | Priority |
|---|---|---|---|
| CRP (C-Reactive Protein) | Acute inflammation | Inflammatory | Essential |
| ESR (Sed Rate) | Chronic inflammation | Inflammatory | Essential |
| Full Blood Count (FBC) | Anaemia, infection, marrow | All types | Essential |
| Vitamin D (25-OH) | Bone/muscle pain source | Musculoskeletal | Essential |
| TSH (Thyroid) | Hypothyroid myopathy | Musculoskeletal | Essential |
| Ferritin + Iron Studies | Iron depletion, restless legs | Musculoskeletal | Essential |
| HbA1c | Diabetes / prediabetes | Neuropathic | Essential |
| Vitamin B12 + Folate | Nerve damage, neuropathy | Neuropathic | Essential |
| Calcium + Magnesium | Cramps, spasms, bone pain | Musculoskeletal | Recommended |
| Uric Acid | Gout | Inflammatory | Recommended |
| Liver Function (LFTs) | Hepatic causes, medication effects | All types | Recommended |
| Kidney Function (eGFR) | Renal pain, uric acid clearance | All types | Recommended |
| Rheumatoid Factor (RF) | Rheumatoid arthritis | Inflammatory | If indicated |
| Anti-CCP Antibodies | Early RA detection | Inflammatory | If indicated |
| ANA (Antinuclear Antibodies) | Lupus, connective tissue disease | Inflammatory | If indicated |
| HLA-B27 | Ankylosing spondylitis | Inflammatory | If indicated |
| CK (Creatine Kinase) | Muscle damage, myopathy | Musculoskeletal | If indicated |
Pain Location Map: Which Tests for Which Pain
Where your pain is located gives your doctor important clues about which blood tests to prioritise. This map connects common pain patterns with their most likely blood-testable causes.
Widespread / All Over
Diffuse pain affecting multiple body regions without a clear anatomical pattern
Likely conditions: Fibromyalgia, vitamin D deficiency (osteomalacia), hypothyroidism, polymyalgia rheumaticaJoints (Symmetrical)
Pain and stiffness in the same joints on both sides - hands, wrists, knees
Likely conditions: Rheumatoid arthritis, lupus, psoriatic arthritisSingle Hot Joint
One intensely painful, swollen, red, warm joint - especially big toe, ankle, or knee
Likely conditions: Gout, pseudogout, septic arthritis (emergency)Burning Feet / Hands
Burning, tingling, numbness, or electric-shock sensations in extremities
Likely conditions: Diabetic neuropathy, B12 deficiency neuropathy, prediabetic neuropathyShoulders & Hips (Over 50)
Severe stiffness and aching in shoulder and hip girdles, worse in the morning
Likely conditions: Polymyalgia rheumatica, giant cell arteritis (check ESR urgently)Muscle Cramps & Spasms
Involuntary painful muscle contractions, twitching, or restless legs
Likely conditions: Magnesium deficiency, calcium deficiency, iron deficiency (restless legs)Lower Back (Inflammatory)
Lower back stiffness worse after rest, improves with movement, onset before age 40
Likely conditions: Ankylosing spondylitis, axial spondyloarthropathyBone Pain (Deep Aching)
Deep aching in ribs, pelvis, shins, or thighs - not joint surfaces
Likely conditions: Osteomalacia, hyperparathyroidism, Paget’s disease, bone metastasesRed Flags: When Chronic Pain Needs Urgent Investigation
Most chronic pain is not dangerous, but certain features require urgent blood tests and medical review. If you recognise any of these patterns, see your GP promptly.
What to Ask Your Doctor
If you have been living with unexplained chronic pain, a clear description of your symptoms helps your GP order the right blood tests first time. Here is a script that covers the key details.
Ready-to-use script for your GP appointment:
“I have been experiencing [widespread aching / burning pain in my feet / joint pain] for [X months]. The pain is [constant / comes and goes / getting worse]. It is [worse in the morning / worse at night / worse with activity]. I also have [fatigue / numbness / muscle cramps / weight change]. Could we run a comprehensive blood panel to check for inflammation, vitamin deficiencies, thyroid function, and blood sugar? I would like to include CRP, ESR, FBC, vitamin D, TSH, ferritin, HbA1c, B12, and calcium.”
CRP (C-Reactive Protein)
ESR (Erythrocyte Sedimentation Rate)
Full Blood Count (FBC)
Vitamin D (25-OH)
TSH (Thyroid Function)
Ferritin + Iron Studies
HbA1c (3-Month Blood Sugar)
Vitamin B12 + Folate
Calcium + Magnesium
Uric Acid
Liver Function Tests
Kidney Function (eGFR, Creatinine)
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