Can the GFR be measured directly?
Yes. The GFR can be measured directly. Radioisotope methods are very accurate but expensive, time-consuming, and invasive. Newer techniques such as serum cystatin appear promising but are significantly more expensive and not as widely available as serum creatinine. The time-honoured method of creatinine clearance requires the extra expense of a timed urine sample that is difficult to collect and analyze accurately.
