The authors base their findings on more than 1100 adults who had sustained a stroke between 1999 and 2004 and had been admitted to hospital in the greater Boston area of Massachusetts in the US.
On admission, each patient's serum creatinine was measured. This is a by-product of muscle metabolism and is filtered out of the body by the kidney, known as the glomerular filtration rate or GFR. The GFR is therefore an indicator of the health of the kidneys and how well they are working.