This blood smear is from a patient with acute renal failure, who presented with a marked accumulation of urea (35 mmol/L; approximately five times the upper limit of the reference range). The creatinine concentration was .

Uremia is associated with the accumulation of uremic toxins, which can cause changes in the lipid composition and membrane stability of erythrocytes. This causes the surface area of the outer membrane layer to increase relatively, leading to the formation of echinocytes: erythrocytes with numerous short, regularly spaced protrusions. This morphological abnormality is usually reversible and may subside following restoration of renal function or after dialysis.