The microbiology lab report on Carlos' stool culture provided some much-needed information--the isolation and growth of Escherichia coli serotype O157: H7. This final, important piece of the diagnostic puzzle led Dr. Williams to a diagnosis: hemolytic uremic syndrome, or HUS.

HUS is a condition in which a gastrointestinal infection with the bacterium E. coli O157: H7 is followed by renal failure, anemia, and thrombocytopenia. Most cases of HUS can be traced back to consuming contaminated food or water. However, some cases result from exposure to the feces of animals that harbor the organism in their gastrointestinal tract. This latter scenario was likely the cause of Carlos' HUS, as he and his family had visited a zoo shortly before the symptoms began.

HUS results when the toxin made by this type of E. coli is absorbed through the intestines into the bloodstream, where it damages all endothelial cells, and in particular the glomerular endothelial cells. This damage to the filtration membrane results in acute renal failure, and explains why Carlos had proteins and cells in his urine that are too large to pass through the undamaged filtration membrane.

The toxin also activates and destroys platelets, leading to thrombocytopenia. Its effects on red blood cells are less direct-they become distorted as they flow through damaged capillaries such as those found in the glomerulus. These distorted red blood cells are then destroyed by the spleen, leading to a condition called hemolytic anemia. We are at last at a point where we know what is wrong with Carlos, but now the question becomes: How will we treat his HUS?

Therapy for HUS is mainly aimed at management of the renal failure, anemia, and thrombocytopenia. As Carlos' anemia and thrombocytopenia were improving, his medical team focused on treating his renal failure, and the treatment of choice for pediatric patients with acute renal failure is peritoneal dialysis. It works by filling the peritoneal cavity with a fluid called a dialysis solution. The dialysis solution contains the sugar dextrose, which draws fluid out of blood vessels by osmosis. As fluid collects in the peritoneal cavity, it pulls wastes such as urea and creatinine out of the blood by diffusion. The dialysis solution remains in the peritoneal cavity for 4-6 hours, after which it is drained away, carrying with it the extra fluid and wastes.

Carlos' medical team needs to measure glomerular filtration rate (GFR) in order to assess his recovery from renal failure. They use creatinine, knowing that this method only provides an estimate of GFR. What limits the usefulness of creatinine?

The microbiology lab report on Carlos' stool culture provided some much-needed information--the isolation and growth of Escherichia coli serotype O157: H7. This final, important piece of the diagnostic puzzle led Dr. Williams to a diagnosis: hemolytic uremic syndrome, or HUS.

HUS is a condition in which a gastrointestinal infection with the bacterium E. coli O157: H7 is followed by renal failure, anemia, and thrombocytopenia. Most cases of HUS can be traced back to consuming contaminated food or water. However, some cases result from exposure to the feces of animals that harbor the organism in their gastrointestinal tract. This latter scenario was likely the cause of Carlos' HUS, as he and his family had visited a zoo shortly before the symptoms began.

HUS results when the toxin made by this type of E. coli is absorbed through the intestines into the bloodstream, where it damages all endothelial cells, and in particular the glomerular endothelial cells. This damage to the filtration membrane results in acute renal failure, and explains why Carlos had proteins and cells in his urine that are too large to pass through the undamaged filtration membrane.

The toxin also activates and destroys platelets, leading to thrombocytopenia. Its effects on red blood cells are less direct-they become distorted as they flow through damaged capillaries such as those found in the glomerulus. These distorted red blood cells are then destroyed by the spleen, leading to a condition called hemolytic anemia. We are at last at a point where we know what is wrong with Carlos, but now the question becomes: How will we treat his HUS?

Therapy for HUS is mainly aimed at management of the renal failure, anemia, and thrombocytopenia. As Carlos' anemia and thrombocytopenia were improving, his medical team focused on treating his renal failure, and the treatment of choice for pediatric patients with acute renal failure is peritoneal dialysis. It works by filling the peritoneal cavity with a fluid called a dialysis solution. The dialysis solution contains the sugar dextrose, which draws fluid out of blood vessels by osmosis. As fluid collects in the peritoneal cavity, it pulls wastes such as urea and creatinine out of the blood by diffusion. The dialysis solution remains in the peritoneal cavity for 4-6 hours, after which it is drained away, carrying with it the extra fluid and wastes.

Carlos' medical team needs to measure glomerular filtration rate (GFR) in order to assess his recovery from renal failure. They use creatinine, knowing that this method only provides an estimate of GFR. What limits the usefulness of creatinine?

a. 15-50% of creatinine may be secreted into the filtrate instead of being filtered.

b. Some creatinine is reabsorbed in the proximal tubule.

c. Creatinine is only secreted into the filtrate.

d. Creatinine is filtered but not secreted or reabsorbed.