Condition · Long Covid and post-viral fatigue
There is no blood test that diagnoses long Covid, and anyone who says otherwise is selling something. What a good panel does is different and more useful: it finds the treatable problems that sit alongside it and are often the real reason you are not recovering. Low-grade inflammation that has not switched off. A thyroid knocked off course by the infection. Ferritin, B12 and vitamin D run down by months of poor appetite and no daylight. A cortisol rhythm that has flattened. Insulin resistance that arrived with the weight and inactivity. And a small set of organ and clotting markers that, if abnormal, are worth a GP appointment in their own right. If you have been told your bloods are normal and you are still not better, the question is what was actually measured.
Venous draw at 103 UK clinics or at home, which matters when leaving the house is the hard part. Report within 48 hours of the lab receiving your sample.
Last reviewed 16 September 2026
The short answer
A long Covid blood panel should cover hs-CRP and a blood count for ongoing inflammation, a full thyroid panel with antibodies for a post-viral thyroid shift, ferritin, B12, folate and vitamin D for the nutrient deficits that stall recovery, morning cortisol and DHEA-S for the stress axis, HbA1c and fasting insulin for new insulin resistance, and liver, kidney and D-dimer or ferritin-based clues that warrant a GP conversation. NICE guidance for post-Covid assessment already recommends most of the first half of that list; the second half is where a comprehensive panel goes further than the standard screen.
Educational, not a substitute for a doctor. New chest pain, breathlessness at rest, a swollen painful calf, or fainting need same-day medical assessment, not a blood panel.
What to test
| Marker | Why it matters after Covid | What to look for | NICE post-Covid screen? | Panel |
|---|---|---|---|---|
| hs-CRP | Low-grade inflammation that has not resolved is the commonest measurable finding; it drives fatigue, brain fog and muscle pain directly | Above 1 mg/L worth explaining; above 3 sustained is a problem to address | Standard CRP, which misses the 1 to 5 range | All panels |
| Full blood count | Lymphocyte and platelet changes after the infection; anaemia from poor intake | Persistent lymphopenia, low haemoglobin, raised platelets | Yes | All panels |
| Thyroid (TSH, free T4, free T3, antibodies) | Viral infection can trigger thyroiditis; a transient overactive phase followed by underactive is well described after Covid, and thyroid fatigue mimics long Covid exactly | TSH out of range in either direction; free T3 low with normal TSH; new positive antibodies | TSH usually | All panels |
| Ferritin, iron studies | Iron stores fall with months of poor appetite; low ferritin causes fatigue, breathlessness on exertion and poor sleep. Ferritin also rises with inflammation, so it must be read against hs-CRP | Ferritin below 30 is deficiency; a normal ferritin with raised hs-CRP may hide a real deficiency (check transferrin saturation) | Sometimes | All panels |
| B12, folate, vitamin D | Run down by reduced eating and no daylight; each independently causes fatigue, low mood and brain fog, and low vitamin D is associated with worse post-Covid outcomes | B12 below 300 pmol/L; folate low; vitamin D below 50 nmol/L | Rarely | All panels |
| Morning cortisol, DHEA-S | Several studies have found lower morning cortisol in long Covid; a flattened rhythm explains the crash after exertion and the unrefreshing sleep | Morning cortisol low in range or below (drawn 8 to 9am); low DHEA-S | No | All panels |
| HbA1c, fasting insulin, HOMA-IR | New insulin resistance and new diabetes are more common after Covid; months of inactivity and weight gain compound it, and unstable glucose worsens fatigue | HbA1c above 38; fasting insulin above 10 mIU/L; HOMA-IR above 2 | HbA1c sometimes; insulin no | HbA1c in all; insulin and HOMA-IR in Ultimate and Signature |
| Liver and kidney (ALT, GGT, eGFR, cystatin C) | Both can be affected by the infection and by the medications taken for it; a muscle-independent kidney reading matters when you have been inactive for months | ALT or GGT raised; cystatin C eGFR lower than creatinine eGFR | Yes, basic | Liver and kidney in all; cystatin C in Ultimate and Signature |
| Sex hormones | Testosterone falls with illness and inactivity in men; perimenopause and long Covid overlap heavily in women over 40 and are frequently confused | Testosterone in the bottom quarter; rising FSH with low oestradiol | No | Core hormones in Advanced; complete set in Ultimate and Signature |
D-dimer, troponin and NT-proBNP are the clotting and cardiac markers a GP may add if you have breathlessness, chest pain or palpitations; they are not in the standard TrueVitals panels and belong in a clinical assessment. Guides: hs-CRP, thyroid, ferritin, B12, vitamin D, cortisol, insulin resistance, kidney.
Read it in context
Something treatable
A ferritin of 18, a vitamin D of 30, a TSH of 5.5 with antibodies, a fasting insulin of 15. None of these is long Covid, and all of them are why you feel like this on top of it. Fixing them does not cure the post-viral illness, but it removes the part of the fatigue that was never post-viral in the first place, and for many people that is most of it.
Inflammation still on
This is the picture that most closely matches what is understood about long Covid itself. It is a reason to pace activity rather than push through it, to look for a source (gums, gut, sinuses, sleep apnoea), and to retest in three months to see the trend. Your report will say so plainly.
All normal
A clean panel across all nine rules out the treatable mimics and confirms that what you have is the post-viral condition itself. That changes the conversation with your GP or long Covid clinic: pacing, graded return, and symptom-specific treatment, without wondering whether something was missed. Always tired and tests normal?
Which panel
Advanced
74 biomarkers · £269
hs-CRP, full blood count, full thyroid with antibodies, ferritin with iron studies, B12, folate, vitamin D, morning cortisol and DHEA-S, HbA1c, liver, kidney, core hormones. Everything on the table except fasting insulin and cystatin C.
View AdvancedAll nine
Ultimate
114 biomarkers · £349
Adds fasting insulin and HOMA-IR, cystatin C, the complete hormone set, Lp(a) and tumour markers. The panel for a recovery that has stalled with no obvious reason.
View UltimateSignature
230 biomarkers · £799
Processed by Randox. Adds an autoimmune profile, a digestive profile and neurological markers, for long Covid with new joint, gut or nerve symptoms.
View SignatureClinic draw £19. At-home £39. Morning appointment, fast from 10pm. Pay monthly available.
Honest comparison
NICE's post-Covid guidance recommends a blood count, kidney and liver function, CRP, ferritin, B12, folate, thyroid function, HbA1c and, where indicated, D-dimer and cardiac markers. If your GP has run that, you have a good baseline and you should ask for a copy. Where a comprehensive panel adds value is the markers outside that list (fasting insulin, morning cortisol, hs-CRP rather than standard CRP, free T3 and antibodies rather than TSH alone, vitamin D, cystatin C, sex hormones) and the interpretation: reading ferritin against hs-CRP so inflammation does not hide a deficiency, and reading the whole picture together rather than as a row of ticks. If you have breathlessness, chest pain or palpitations, the GP route comes first and the panel sits alongside it. What to ask your GP for.
After your result
Each marker explained in context, with the deficiencies and shifts that are fixable flagged first, and the inflammatory picture described honestly.
Iron, B12, vitamin D and folate are corrected with supplements at the right dose. A thyroid shift, a raised liver enzyme or a hormone result needs a prescriber, and the report tells you which results to bring.
Recovery from post-viral illness is measured in months. The second report shows whether hs-CRP is falling, whether the nutrients have refilled and whether the thyroid has settled, which is the objective evidence a symptom diary cannot give you. Retest plans.
FAQs
No. Long Covid is diagnosed on symptoms and history after other causes are excluded. Research markers exist but none is validated for diagnosis. What a panel does is find the treatable problems that sit alongside it, which is often where the biggest improvement is.
hs-CRP and a blood count, a full thyroid panel with antibodies, ferritin with iron studies, B12, folate and vitamin D, morning cortisol and DHEA-S, HbA1c with fasting insulin, liver and kidney function including cystatin C, and sex hormones. That covers the NICE post-Covid list plus the markers it leaves out.
Usually yes, for two reasons. The GP screen typically omits fasting insulin, cortisol, vitamin D, free T3 and antibodies, and uses standard CRP rather than high-sensitivity, so the grey-zone results that explain most persistent fatigue are not seen. And a fully normal comprehensive panel is itself valuable: it confirms the post-viral diagnosis and stops the search for something missed.
Yes. Post-viral thyroiditis, sometimes with a temporary overactive phase followed by an underactive one, is well described after Covid, and new thyroid antibodies can appear. Thyroid fatigue is indistinguishable from long Covid fatigue without the blood test.
Several studies have found lower morning cortisol in people with long Covid compared with recovered controls. It is not diagnostic, but a flattened rhythm helps explain post-exertional crashes and unrefreshing sleep, and it is worth knowing before deciding how hard to push activity.
Yes. A registered phlebotomist visits your home for £39 and takes the same venous sample a clinic would, which matters when a bad day would otherwise mean cancelling. Morning slots are available. How at-home testing works.
Advanced and Ultimate reports are delivered within 48 hours of the laboratory receiving your sample. Signature takes around 12 working days.
Nine post-viral markers in one venous draw, at a clinic or at home, with a report within 48 hours that separates what is fixable from what needs time.
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