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Table 1 Salient features of various methods that could be employed to measure GFR in ICU setup

From: Estimation of renal function in the intensive care unit: the covert concepts brought to light

Sl no Methods Merits Demerits
1 CG formula Easily computable Highly inaccurate in the critical care setup. Considerable degree of GFR overestimation
2 4-variable MDRD More accurate than CG. May offer value close to 6-variable MDRD in healthier patients with preserved BUN/Cr ratio Dependency on creatinine. May not be accurate when BUN/Cr ratio is increased. Does not take into account blood urea nitrogen and albumin. Overestimation of GFR when baseline GFR is high
3 6-variable MDRD BUN and serum albumin are taken into account. More accurate when BUN/CR ratio is increased. Better concordance correlation coefficient when compared with CG and 4-variable MDRD Dependency on creatinine. Ongoing creatinine production and its fluid balance variations are not taken into account. Less accurate when compared with cystatin C and novel methods
4 CKD-EPI formula Greater precision and reliability when compared with MDRD. More accurate when GFR >60 ml/min/1.73 m2 Not validated extensively in hospitalized and sick individuals. Dependency on serum creatinine
5 24-h creatinine clearance More accurate when compared to CG and MDRD formulae Collection of urine is an issue. Cannot provide immediate results. Becomes a problem when rapid administration of drugs is essential
6 Jelliffe's equation Ongoing creatinine production and fluctuations in creatinine concentration over time are taken into account Does not take into account the variations in creatinine concentration with respect to fluid balance
7 Modified Jelliffe's equation Fluid balance variations of creatinine are also taken into account Still less accurate when compared with cystatin C and fiberoptic radiometric methods
8 Serum cystatin C Less affected by non-renal factors. Sensitive to changes in so-called creatinine blind GFR(40–70 ml/min); preferred agent in liver disease patients Expensive and unreliable in the presence of thyroid dysfunction, may be affected in patients taking high dose steroids with renal dysfunction
9 Aminoglycoside clearance May serve as an easy method for GFR estimation in patients already on aminoglycosides. May be better than 24-h creatinine clearance Giving aminoglycoside for renal function estimation alone may not be wise or practically possible
10 Fiberoptic ratiometric fluorescent analyzer method Most accurate way of all. Rapid, inexpensive, reproducible, and safe method Still experimental. Requirement of technical expertise. Scarce studies in humans