NephrologyTier 2Topic

Laboratory tests - full blood count (FBC) in kidney disease

Focus in nephrology

In nephrology, the FBC is dominated by the normochromic normocytic anaemia of CKD (see renal disease and anaemia for full detail) and clues to underlying/associated systemic disease
Anaemia becomes increasingly prevalent as eGFR falls, near-universal by dialysis-dependent CKD without treatment

Anaemia of CKD

Reduced erythropoietin production by the diseased kidney is the dominant mechanism (see erythropoietin production for the physiology); iron deficiency, chronic inflammation, and reduced red cell survival in uraemia all contribute additionally

Clues on the film and differential

Schistocytes/fragments on the film raise suspicion for thrombotic microangiopathy (HUS/TTP, malignant hypertension, scleroderma renal crisis) as the cause of the renal impairment, not just a consequence of it
Eosinophilia - a clue to acute interstitial nephritis (drug-induced) or vasculitis as the cause of AKI

Acting on the result

Anaemia of CKD workup/management - see renal disease and anaemia (iron studies first, then erythropoiesis-stimulating agents)
Schistocytes + AKI + thrombocytopenia -> urgent haematology/nephrology co-management (TMA workup, consider plasma exchange)

Associations

Anaemia of CKD, thrombotic microangiopathy, acute interstitial nephritis, multiple myeloma (cast nephropathy - anaemia + renal failure + bone pain)

Consequences

Anaemia of CKD contributes to fatigue and left ventricular hypertrophy if untreated - part of the rationale for correction, not simply a lab abnormality

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