🔋 Chronic Fatigue Workup

What this panel can settle, and by what logic

Twelve markers, and the value is in four pairings rather than in twelve separate answers. Each pairing settles something neither half settles alone.

1. Ferritin beside a Complete Blood Count (CBC) with Differential separates depletion from anemia. Iron stores empty first and hemoglobin falls last, so a ferritin of 15 ng/mL with a hemoglobin of 13.5 g/dL is a real finding that a CBC alone reports as normal. No single cut-off works everywhere: a 2025 review exists because a global ferritin threshold for iron deficiency has still not been agreed Cancado 2025, which is why this panel reads ferritin against the Iron Panel (Iron, TIBC, Transferrin Saturation) saturation rather than against one number.
2. Vitamin B12 beside Methylmalonic Acid (MMA) separates a low number from a real deficiency. Serum B12 counts what is circulating, most of it bound to haptocorrin and unavailable to any cell. Methylmalonic acid accumulates only once the B12-dependent mutase step has actually stalled, which makes MMA the functional test rather than a second opinion Harrington 2024. A B12 of 320 pg/mL with an MMA of 0.60 µmol/L is deficiency; the same 320 pg/mL with a normal MMA is not.
3. hs-CRP (High-Sensitivity C-Reactive Protein) is not a finding on this panel, it is the interpreter. Ferritin is an acute-phase protein, so a ferritin drawn during inflammation overstates the stores behind it. The BRINDA method exists to correct micronutrient biomarkers for exactly this Luo 2023. A ferritin of 60 ng/mL with a CRP of 8 mg/L is not the same fact as 60 ng/mL with a CRP of 0.4 mg/L.
4. TSH (Thyroid-Stimulating Hormone) beside Free T3 (Triiodothyronine) catches the case the pituitary hides. TSH is the right first test and a free T3 of 2.4 pg/mL under a TSH of 1.8 mIU/L is a pattern TSH alone cannot show you.

The panel also carries the one result on it that is urgent rather than interesting: a Cortisol (AM) drawn before 9am and low needs a doctor the same week Ramadoss 2021.

What it cannot settle, and what would

It cannot detect sleep apnea, and sleep apnea is the commonest thing this panel gets bought instead of. Obstructive sleep apnea produces the exact presentation on this page, exhausted after 8 hours in bed, and there is no blood marker for it at any price Platon 2023. The test is a sleep study. If all 12 markers come back optimal and you snore, this panel was the wrong $300.

It cannot tell you why the iron is low, which is the question that matters in a man or a postmenopausal woman. A ferritin of 12 ng/mL says the stores are empty; it does not separate intake, absorption, menstrual loss and slow gastrointestinal bleeding, and only one of those four is treated with a supplement.

It carries no celiac serology. Untreated celiac disease malabsorbs both iron and B12 Harrington 2024, so if ferritin falls again within 6 months of successful replacement, tissue transglutaminase antibodies are the next test and a second course of iron is not.

And it cannot diagnose chronic fatigue syndrome or depression. Both are clinical diagnoses made by excluding what is on this list, which is a real use for the panel — but it means 12 normal results are an answer rather than a wasted 2 weeks.

Draw conditions that decide whether the money is wasted

Four conditions, ranked by how much of the panel each one ruins.

1. Cortisol (AM) before 9am, or do not draw it at all. Cortisol falls steeply across the day, so an afternoon value cannot be read against a morning interval. A series written to stop these being misread found a cut-off of 234 nmol/L that missed nobody, at a specificity of 59.5% Ramadoss 2021 — even a purpose-built threshold sends 4 in 10 people for a stimulation test they did not need.
2. No biotin for 72 hours. Hair and nail supplements carry 5,000 to 10,000 mcg, and biotin at those doses interferes with streptavidin-based immunoassays, pushing TSH (Thyroid-Stimulating Hormone) and Free T3 (Triiodothyronine) in opposite directions Li 2020. That is the precise shape of a thyroid result somebody acts on.
3. Not within 2 weeks of an infection. Ferritin and hs-CRP both rise as acute-phase proteins, so the iron half of a 12-marker panel becomes uninterpretable at the moment it looks most reassuring Luo 2023.
4. Stop oral iron 5 to 7 days before. Serum iron and transferrin saturation track the last tablet, not the stores; Ferritin is the slow number and the one worth paying for.

How you would know it answered your question, and what each pattern means next

Six patterns, and what each means for the next 12 weeks.

• Ferritin under 30 ng/mL with a normal Complete Blood Count (CBC) with Differential: iron deficiency without anemia. Treat, then retest at 12 weeks, not at 4 — a store that took months to empty refills over months, and an early value mostly reads yesterday's dose Cancado 2025.
• Ferritin 30 to 100 ng/mL with hs-CRP (High-Sensitivity C-Reactive Protein) over 3 mg/L: not readable as it stands. Read the Iron Panel (Iron, TIBC, Transferrin Saturation) saturation instead and redraw both when CRP is under 1 mg/L Luo 2023.
• Vitamin B12 of 150 to 350 pg/mL with a raised Methylmalonic Acid (MMA): functional deficiency behind an in-range number. MMA falls within 4 weeks of adequate B12, so MMA is the marker to recheck and serum B12 is not Harrington 2024.
• TSH (Thyroid-Stimulating Hormone) over 4 mIU/L with a low Free T3 (Triiodothyronine): add Thyroid Antibodies (TPO + TgAb) and take it to a clinician. Retest at 8 weeks — the pituitary needs 6 to 8 weeks to re-equilibrate after any change in thyroid supply, so a 3-week recheck reads the old set point.
• Low morning Cortisol (AM): the one result here that does not wait. Add ACTH (Adrenocorticotropic Hormone) and see a doctor Ramadoss 2021.
• All 12 optimal: the panel worked. The next test is a sleep study Platon 2023, and a second identical panel in 8 weeks will almost certainly say the same thing for the same $300.

Sources read for these sections

• Cancado RD. Defining Global Thresholds for Serum Ferritin: A Challenging Mission in Establishing the Iron Deficiency Diagnosis in This Era of Striving for Health Equity. Diagnostics (Basel) 2025 · PMID 39941219
• Luo H, et al. A Practical Guide to Adjust Micronutrient Biomarkers for Inflammation Using the BRINDA Method. Journal of Nutrition 2023 · PMID 36792034
• Harrington DJ. The application and interpretation of laboratory biomarkers for the evaluation of vitamin B12 status. Annals of Clinical Biochemistry 2024 · PMID 39367523
• Platon AL, et al. An Update on Obstructive Sleep Apnea Syndrome-A Literature Review. Medicina (Kaunas) 2023 · PMID 37629749
• Ramadoss V, et al. Improving the Interpretation of Afternoon Cortisol Levels and SSTs to Prevent Misdiagnosis of Adrenal Insufficiency. Journal of the Endocrine Society 2021 · PMID 34611573
• Li D, Ferguson A, Cervinski MA, Lynch KL, Kyle PB. AACC Guidance Document on Biotin Interference in Laboratory Tests. J Appl Lab Med 2020 · PMID 32445355