Persistent exhaustion—often called TATT (Tired All The Time) by medical professionals—is one of the most common reasons for doctor visits.
Whilst lifestyle factors are often to blame, unexplained tiredness should always be investigated to rule out underlying pathology.
If you have been suffering from chronic fatigue, a physical examination and a comprehensive blood panel are the first steps toward a diagnosis.
Below is a clinical “gold standard” list of 18 blood tests used by hospital specialists to investigate fatigue.
These tests look at the physical makeup of your blood to identify oxygen-carrying capacity and signs of systemic stress.
Full Blood Count (FBC): Screens for anaemia (low iron), polycythaemia (too many red cells), and haematological malignancies like leukaemia.
Ferritin, B12 and Folate: Deficiencies in these nutrients are leading causes of fatigue, even before full-blown anaemia develops.
ESR and CRP: These act as “trouble at the mill” tests. If raised, they suggest chronic infection, inflammation, or autoimmune disease.
Clinical Note: Interestingly, CRP can sometimes remain low even in active SLE (Lupus).
Fatigue is often a secondary symptom of your internal organs struggling to filter waste or balance chemistry.
Urea and Electrolytes (U&Es): These assess Chronic Kidney Disease (CKD) and electrolyte imbalances (sodium, potassium).
Creatine Kinase (CK): A specific marker used to identify muscle inflammatory disorders.
Liver Function Tests (LFTs): These detect various stages of liver disease.
Bone Biochemistry: Includes Magnesium, Vitamin D, and Urate (to screen for gout).
Your endocrine system controls your “internal thermostat” and energy usage.
Thyroid Function Tests (TFTs): Measures TSH and T4 to diagnose an underactive (hypo) or overactive (hyper) thyroid.
HbA1c and Glucose: The primary screening tool for Type 1 and Type 2 Diabetes.
9am Cortisol: A morning blood draw to exclude adrenal insufficiency (Addison’s Disease).
If the body’s immune system is attacking its own tissues, profound exhaustion is often the first sign.
Coeliac Disease Screen (IgA tTG): Screens for Coeliac Disease, which frequently presents as tiredness without digestive symptoms.
Autoimmune Screen (ANA/RhF): Screens for Lupus and Rheumatoid Arthritis, which can exist without obvious rashes or joint pain.
PSA (Prostate-Specific Antigen): Recommended for men to screen for prostate issues.
Myeloma Screen: Specialised tests (Serum Protein Electrophoresis) to look for specific blood cancers.
Lingering viral or bacterial loads can drain the body’s energy reserves for months.
Monospot Test: To diagnose Glandular Fever.
Hepatitis B/C and HIV: Screening for chronic viral infections.
Lyme Disease: An antibody test for those exposed to tick bites.
Syphilis Screen: Often overlooked but a necessary screen for chronic fatigue.
EBV and CMV: Testing for latent viral infections.
Blood tests provide a large piece of the puzzle, but they aren’t the whole picture. Your doctor may also require:
| Test Type | Purpose |
| Urinalysis | Checking for protein, blood, or glucose (UTI/Kidney issues). |
| Sputum Samples | Screening for Tuberculosis (TB). |
| Chest X-Ray | To rule out lung disease or TB. |
| CT Scan (CAP) | A CT of the Chest, Abdomen, and Pelvis if all other tests are inconclusive. |
There is currently no specific diagnostic blood test for Chronic Fatigue Syndrome (ME/CFS) or Long COVID. These are “diagnoses of exclusion,” confirmed only after the tests above have ruled out other causes.
Don’t just wait for a text saying your results are “satisfactory.” Sometimes, your levels might be at the very bottom of the “normal” range (e.g. low-normal Ferritin or Vitamin D), which can still cause symptoms.
Ask the receptionist for a printed or digital copy of your blood tests so you can keep track of your own health trends over time.
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