Kidney Function

Background: Information about iron stores and their relationship with transferrin saturation (TSAT), serum ferritin, and the erythropoietic response to iron therapy is scarce in anemic non–dialysis-dependent patients with chronic kidney disease (CKD). We examined the diagnostic utility of peripheral-iron indices and the erythropoietic response to intravenous iron as indices of iron store depletion using bone marrow iron as a reference test in anemic non–dialysis-dependent patients with CKD.Study Design: Diagnostic test study.Setting & Participants: 100 anemic (hemoglobin <11 g/dL) patients with CKD stages 3-5, not receiving epoetin and iron.Index Tests: TSAT index and serum ferritin level at baseline and increase in hemoglobin level 1 month after 200 mg of iron sucrose daily for 5 days.Reference Test: Bone marrow iron (assessed using aspiration and Perls’ stain), depleted versus replete, at baseline.Measurements: Area under the receiver operating characteristic curve (AUROC), sensitivity, and specificity of peripheral-iron indices and erythropoietic response to describe bone marrow iron stores.Results: Bone marrow iron stores were depleted in 48% of patients at baseline. In iron-depleted versus -replete subjects, mean hemoglobin level, median TSAT index, median serum ferritin level, and hemoglobin level increase after iron sucrose administration were 8.74 ± 1.1 (SD) versus 9.22 ± 0.9 g/dL (P = 0.02), 19% (interquartile range [IQR], 15%) versus 28% (IQR, 12%; P < 0.001), 100 (IQR, 131) versus 220 ng/mL (IQR, 213; P < 0.001), and 1.2 ± 0.4 versus 0.8 ± 0.3 g/dL (P < 0.001), respectively. TSAT, ferritin level, and increase in hemoglobin level AUROCs were similar: 0.75 (95% CI, 0.66-0.85), 0.76 (95% CI, 0.66-0.85), and 0.74 (95% CI, 0.65-0.84), respectively.Limitations: Bone marrow iron as the index of iron stores.Conclusions: Half the anemic patients with CKD stages 3-5 had depleted iron stores. Peripheral-iron indices and erythropoietic response had equivalent, but limited, utility in identifying depletion of bone marrow iron stores. Use of these indices to indicate depletion of iron stores should be reconsidered.

Nephrotic syndrome is characterized by heavy proteinuria (protein excretion >3.5 g/24 h in adults or 40 mg/m2/h in children), hypoalbuminemia (albumin <2.5 g/dL), edema, and hyperlipidemia. Edema results from fluid accumulation in the subcutaneous tissue. Fluid also commonly accumulates in the peritoneal and pleural cavities. Rarely, fluid may accumulate in the subcapsular space around the kidneys. Such subcapsular fluid accumulation has been reported as a complication of nephrotic syndrome or in association with severe pulmonary hypertension. We describe a patient with nephrotic syndrome who presented with hypertension and pain in the left lumbar region. Ultrasonography and magnetic resonance imaging (MRI) showed a massive subcapsular collection around the left kidney. The patient was treated successfully with ultrasonography-guided drainage of the collection and medical treatment. The kidney biopsy specimen showed changes of focal segmental glomerulosclerosis.

It currently is unknown whether creatine supplementation is safe for people with or at risk of kidney disease. We report on the short-term effects of creatine supplementation on kidney function in a young man with a single kidney and mildly decreased glomerular filtration rate (GFR). A 20-year-old man who had undergone unilateral nephrectomy and presented with mildly decreased GFR without kidney damage underwent a trial with 35 days of creatine supplementation (20 g/d for 5 days followed by 5 g/d for the next 30 days) and had his kidney function monitored. After the intervention, 51Cr-EDTA clearance (pre, 81.6 mL/min/1.73 m2; post, 82.0 mL/min/1.73 m2), proteinuria (protein excretion: pre, 130 mg/d; post, 120 mg/d), and electrolyte levels were unchanged. Albuminuria, serum urea level, and estimated creatinine clearance were decreased (pre, 4.6 mg/d; post, 2.9 mg/d; pre, 37 mg/d; post, 28 mg/dL; and pre, 88 mL/min/1.73 m2; post, 71 mL/min/1.73 m2, respectively), whereas serum creatinine level was slightly increased (pre, 1.03 mg/dL; post, 1.27 mg/dL), falsely suggesting kidney function impairment. This prospective report suggests that short-term creatine supplementation may not affect kidney function in an individual with a single kidney, mild decreased GFR, and ingesting a high-protein diet (ie, 2.8 g/kg/d). This finding has great relevance considering that creatine-induced kidney disease has been a growing concern, even for healthy people.