What are the common abnormal urinary findings in SCD?
• Hematuria: Both microscopic and macroscopic hematuria may be observed. The left kidney is affected four times greater than the right due to the increased venous pressure within the longer left vein that is compressed between the aorta and the superior mesenteric artery. This is known as the “nutcracker phenomenon.” The increased venous pressure leads to increased relative hypoxia in the renal medulla, hence sickling. In 10% of cases, hematuria occurs bilaterally. Hematuria may also indicate the presence of papillary necrosis and, in rare cases, renal medullary carcinoma. The latter is predominantly observed in sickle cell trait rather than SCD.
• Proteinuria: The prevalence of albuminuria and proteinuria is 30% within the first three decades of life and increases up to 70% in older patients. Proteinuria may be associated with defects in glomerular permselectivity, tubular injury, and/or specific single nucleotide polymorphisms in the APOL1 genes.
• Bacteriuria: Patients with SCD may be at increased risk for urinary tract infections from encapsulated organisms due to autosplenectomy, abnormally dilute and alkaline urine (more favorable for bacterial growth compared with hypertonic and acidic urine), and papillary necrosis. However, significant bacteriuria generally occurs in less than 10% of sickle cell patients, half of whom are asymptomatic.
