Children with Thalassemia Major Display Abnormal Renal Tubular Function

Introduction. Chronic hypoxia, transfusional iron overload and chelation therapy are all contributing factors to the deterioration of renal function in thalassemia major (TM ) patients. Among chelators, deferasirox (DFX) is considered the most toxic drug for kidneys: increment of more than 30% of serum creatinine levels is used for dosage modulation or interruption. Recently tubular abnormalities have also been described. We have observed renal toxicity in nine children affected by TM and treated with DFX or deferiprone (DFP) and described the differences in glomerular or tubular function between the two oral chelators.

Material and methods. Nine children, 4 males and 5 females, aged 3-17 years (median 7 y), were retrospectively evaluated. They were regularly transfused every 2-3 weeks, receiving a median of 260 g erythrocytes concentrates/kg/year. The median serum ferritin level at baseline before starting oral chelation was 1763 ug/L (range 1127-4198).

Four patients (pts) received only one type of chelator (1 DFP and 3 DFX). Five pts received both DFX or DFP in different periods. Overall 8 DFX treatments (dosage 15-30 mg/kg, for 18-112 months, mean 40) and 6 DFP treatments (dosage 75-130 mg/kg for 14-54 months, mean 24) were administered. Three pts had previously received deferoxamine; 3/8 DFX pts and 1/6 DFP pts were naïf to chelation before first renal evaluation.

The following renal indices were considered:

− glomerular function: serum creatinine and cystatine C levels, estimated glomerular filtration rate (eGFR), according to modified Schwartz formula; urine albumin to creatinine ratio (ACR), urine protein excretion.

− tubular function: glycosuria, urinary N-acetyl-beta-D-glucosamidase activity/u-creatinine (u-NAG/u-cr), (index of acute tubular damage); urine daily Beta2 microglobulin (B2MG) and Alfa1 microglobulin (A1MG) excretion (both indices of chronic tubular damage).

Analyses were performed at different intervals, according to clinical conditions and patients' age, with different frequency among children.

Creatinine impairment was defined as an increase over 30% of basal level. All indices were graded according to local laboratory range. Toxicity was considered significant when the tests were abnormal in at least 25% of evaluations.

Results. Initial renal function was normal in all patients (median eGFR 209 ml/min/1.73 m2, range 157-295) and eGFR remained stable over time in all cases. A total of 5 pts with DFX and 3 pts with DFP showed an increase of creatinine over 30% of basal levels. Increase of ACR > 30 mg/g cr was seen in 6/8 pts (75%) in DFX and in 1/6 pts (17%) in DFP; 2 pts (1/8 in DFX and 1/6 in DFP) had macroalbuminuria (ACR >300 mg/g creatinine). No association was found between cumulative DFP dose and eGFR over time (Pearson coefficient, r = 0.06), while a moderate association was found with DFX (r = 0.5; p = 0.06).

Symptomatic acute tubular toxicity was observed in 2 pts, with tubular acidosis, glycosuria and abnormal acute tubular indices (u-NAG/u-cr). A1MG and B2MG were also altered, suggesting a chronic injury substrate. Both pts were in DFX group (receiving a dose of 20 and 40 mg/kg/day, respectively) and had experienced a fast reduction in ferritin levels over a short period of time. No signs of concomitant infection were detected.

u-NAG/u-cr was always abnormal in all children in both groups; mean values were 2.8 U/mmol for DFX and 2.4 U/mmol for DFP. B2MG was altered in 6/8 DFX pts and in 2/6 DFP pts (75% vs 33%). Median values were 3.0 mg/24 h for DFX and 0.5 mg/24 h for DFP, respectively. A1MG was altered in 4/8 DFX pts and 3/6 DFP pts, with median values of 164 mg/24 h for DFX and 55 mg/24 h for DFP, respectively.

Conclusions. Patients withTM can experience abnormalities in renal function, especially as regards tubular damage. Acute tubular damage indices were altered in all chelated pts, whereas tests for chronic damage were abnormal more often in the DFX group than in DFP-treated pts. Albeit the significance of our findings needs further confirmation in a longer follow up, these results suggest that extensive renal evaluation is needed, in particular in children whose life expectancy is open and long-term prognosis for multiple organ function is an important issue.