Blood Tests for Pruritus Workup
All patients with generalized pruritus should receive a core panel of blood tests including: complete blood count with ferritin, liver function tests, and renal function (urea and electrolytes). 1, 2
Core Initial Laboratory Panel (Order for All Patients)
The British Association of Dermatologists establishes these as essential first-line investigations for chronic generalized pruritus without rash 1, 2:
- Complete blood count (CBC) - screens for hematological disorders including polycythemia vera, lymphoma, and anemia 1, 2
- Ferritin levels - iron deficiency is the most common systemic cause of pruritus, accounting for 25% of cases 3
- Liver function tests (LFTs) - evaluates for cholestatic liver disease, a major cause of generalized pruritus 1, 2
- Urea and electrolytes - screens for chronic kidney disease and uremic pruritus 1, 2
Critical Pitfall: Ferritin Interpretation
Ferritin is an acute-phase reactant and may be falsely elevated despite true iron deficiency 3. If clinical suspicion for iron deficiency remains despite "normal" ferritin, order serum iron and total iron binding capacity 2, 3.
Additional Tests Based on Clinical Suspicion
When Hematological Disease is Suspected
Order these if CBC shows abnormalities or clinical features suggest blood disorders 1, 2:
When Polycythemia Vera is Suspected
If hemoglobin or hematocrit is elevated 1, 2:
- JAK2 V617F mutation analysis - diagnostic for polycythemia vera 1, 2
- Refer to hematology if positive or if suspicion remains high 1
When Liver Disease is Suspected Beyond Basic LFTs
Consider these additional hepatic investigations 1:
When Infectious Causes are Considered
Particularly with relevant travel history or risk factors 1, 2:
- HIV serology 1, 2
- Hepatitis A, B, and C serology 1, 2
- Malaria, strongyloidiasis, and schistosomiasis screening (if travel history warrants) 1
Tests NOT Routinely Recommended
Avoid These Unless Specific Clinical Features Present
Thyroid function tests - only order if clinical features suggest thyroid disease, diabetes, or other endocrinopathy 1. The 2024 JAMA review suggests thyroid testing as part of initial workup 4, but the British Association of Dermatologists guideline specifically recommends against routine thyroid testing without clinical indicators 1. In clinical practice, given the low yield and guideline recommendation, avoid routine thyroid testing unless symptoms suggest endocrine disease.
Extensive malignancy screening - thorough history and physical examination should guide targeted investigations; full cancer workup is not routinely recommended 1
Algorithm for Persistent Unexplained Pruritus
If initial blood work is unrevealing and pruritus persists 1, 2:
- Consider skin biopsy - to evaluate for cutaneous lymphoma or small fiber neuropathy 1, 2
- Review all medications - drug-induced pruritus requires medication cessation trial rather than additional blood tests 1
- Refer to appropriate specialist based on clinical suspicion (hematology, hepatology, nephrology) 1