RBC, WBC and platelet analysis — first-line for infection, anaemia and bleeding work-up.
HbTLCDLCPlateletsMCVMCHRDW
Anaemia (low Hb)
Common causes
- • Iron / B12 / folate deficiency
- • Chronic disease
- • Haemolysis
- • Bone marrow failure
- • Acute blood loss
Significance: Reduced oxygen-carrying capacity; classify by MCV first (micro/normo/macrocytic).
Differential diagnosis
- • IDA
- • Thalassaemia trait
- • ACD
- • Megaloblastic anaemia
- • Haemolytic anaemia
- • Aplastic anaemia
Next investigations
- • Peripheral smear
- • Reticulocyte count
- • Iron studies
- • B12/folate
- • LDH, bilirubin, haptoglobin
- • Coombs
Red flags
- • Hb <7 g/dL
- • Active bleeding
- • Haemodynamic instability
- • Bicytopenia/pancytopenia
Leukocytosis
Common causes
- • Bacterial infection
- • Steroids
- • Stress / trauma
- • Leukaemia
- • Myeloproliferative disorder
Significance: Non-specific — interpret with DLC and clinical picture.
Differential diagnosis
- • Sepsis
- • Abscess
- • AML/CML
- • Leukemoid reaction
Next investigations
- • Peripheral smear
- • Cultures
- • CRP / procalcitonin
- • Imaging for source
Red flags
- • TLC >30 with blasts
- • Left shift with toxic granulation
- • Severe sepsis criteria
Thrombocytopenia
Common causes
- • Sepsis / DIC
- • ITP / TTP
- • Drug-induced
- • Liver disease
- • Hypersplenism
- • Marrow failure
Significance: Bleeding risk increases <50,000; spontaneous bleeding <20,000.
Differential diagnosis
- • ITP
- • TTP/HUS
- • DIC
- • HIT
- • Dengue
- • Aplastic anaemia
Next investigations
- • Peripheral smear (schistocytes?)
- • Coag profile
- • LDH, retic, bilirubin
- • Viral markers
- • BM biopsy if isolated
Red flags
- • Platelets <20,000
- • Active bleeding
- • MAHA on smear (TTP)
- • DIC pattern
Educational support only — not a substitute for clinical judgment.
