Itch With Rash vs Without Rash
The first clinical distinction is whether itching is accompanied by a visible skin rash. This guides the investigation approach:
- Itch with rash: More likely a primary skin condition (eczema, urticaria, scabies, psoriasis, contact dermatitis). Dermatology evaluation is first priority.
- Itch without visible rash (pruritus sine materia): More likely a systemic (internal) medical cause. Blood tests are the essential investigation.
Systemic Causes of Itch Without Rash
| Cause | Mechanism | Key Blood Test |
|---|---|---|
| Liver disease / Cholestasis | Bile salts accumulate in skin when bile cannot drain normally | LFT (bilirubin, ALP, GGT), hepatitis serology |
| Chronic Kidney Disease (CKD) | Uraemic toxins build up; calcium-phosphate deposits in skin | KFT (creatinine, urea, eGFR) |
| Hypothyroidism | Dry skin from reduced skin moisture and slowed metabolism | TSH |
| Iron deficiency (without anaemia) | Iron-dependent enzymes affect itch-modulating pathways | Serum ferritin, TIBC |
| Polycythaemia vera | Aquagenic pruritus (itch after warm water) classic; mast cell degranulation | CBC (elevated haematocrit, raised haemoglobin, raised platelets) |
| Lymphoma (Hodgkin's) | Cytokine release; generalised pruritus is a B-symptom | CBC, LDH, ESR |
| Diabetes mellitus | Peripheral neuropathy, dry skin, yeast infections (candida) | HbA1c, fasting glucose |
| Allergy / Atopy | IgE-mediated; histamine release from mast cells | Total IgE, specific IgE, CBC eosinophils |
Blood Tests to Order for Pruritus
- LFT — Liver enzymes, bilirubin (cholestasis causes intense pruritus especially at night)
- KFT (creatinine, urea, eGFR) — Kidney function; uraemia causes intractable itch
- TSH — Thyroid disease (both hypo and hyperthyroidism can cause itch)
- CBC with differential — Polycythaemia vera (high haematocrit), lymphoma markers (lymphocytosis), eosinophilia
- Ferritin and TIBC — Iron deficiency even without anaemia can cause itch
- HbA1c — Diabetes-related skin and nerve changes
- Total IgE and eosinophil count — Allergic cause
Treatment by Cause
Systemic pruritus resolves when the underlying cause is treated. General measures for symptomatic relief include: moisturising regularly, cool baths, loose cotton clothing, antihistamines (cetirizine or loratadine), and avoiding scratching (which worsens the itch-scratch cycle). Specific treatments include cholestyramine for cholestatic itch, erythropoietin for uraemic pruritus, and iron supplementation for iron deficiency.
Questions to Ask Your Doctor
- Should we check liver and kidney function given the itch is without a rash?
- Do I need ferritin checked even if my haemoglobin is normal?
- Could this be related to lymphoma — are there other symptoms I should watch for?
- What antihistamine is appropriate while we investigate?
- Do I need a skin biopsy or dermatology referral?
Medical Disclaimer: This information is for educational purposes only. Persistent itching without rash can indicate serious systemic disease and warrants proper medical evaluation.