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 >60Â ml/min/1.73Â 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 |