Interest and limits of glomerular filtration rate (GFR) estimation with formulae using creatinine or cystatin C in the malnourished elderly population

Inappropriate Prescription and Renal Function Among Older Patients with Cognitive Impairment

BACKGROUND

Older people are more sensitive to drugs and adverse drug reactions than younger people because of age-related physiological changes such as impaired renal function. As people with dementia are particularly vulnerable to the effects of drugs, it is especially important to evaluate the dosages of renally cleared medications in this group.

OBJECTIVE

The aim of this study was to estimate the prevalence of impaired renal function and inappropriate prescriptions on the basis of renal function among older patients with dementia or cognitive impairment.

METHODS

The medical records of 428 patients aged ≥65 years who were admitted to two hospitals in northern Sweden were reviewed and renally cleared medications were identified. The Cockcroft-Gault equation was used to evaluate renal function. Doses were evaluated according to the Geriatric Dosage Handbook.

RESULTS

Renal function was impaired (estimated glomerular filtration rate <60 ml/min) in 65.4 % of the study population. Impaired renal function was associated with increasing age. Among 547 prescriptions identified as renally cleared medications, 9.1 % were inappropriate based on the patient's renal function; 13.5 % of the 326 patients prescribed renally cleared medications had inappropriate prescriptions. Inappropriate prescriptions were more common among patients living in nursing homes.

CONCLUSIONS

Impaired renal function is common and inappropriate prescription is prevalent among old people with cognitive impairment in northern Sweden. Continuous consideration of renal function is important when prescribing medications to this group.

Renal function assessment in older adults

AIMS

The Cockcroft-Gault (CG), the Modification of Diet in Renal Disease (MDRD) and the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) formulae are often used to estimate glomerular filtration rate (GFR). The objective was to determine the best method for estimating GFR in older adults.

METHODS

A cross-sectional study was conducted at the geriatric wards of two hospitals in The Netherlands. Patients aged 70 years or above with an estimated (e)GFR below 60 ml min⁻¹  1.73 m⁻² were included. The CG, CG calculated with ideal bodyweight (IBW), MDRD and CKD-EPI formulae were compared with a criterion standard, sinistrin clearance. Renal function was classified into five stages according to the National Kidney Foundation Disease Outcomes Quality Initiative chronic kidney disease classification, as follows (in ml min⁻¹  1.73 m)⁻²: stage 1, eGFR ≥ 90; stage 2, eGFR of 60-89; stage 3, eGFR of 30-59; stage 4, eGFR of 15-29; and stage 5, eGFR < 15.

RESULTS

Sixteen patients, 50% male, with a mean age of 82 years (range 71-87 years) and mean body mass index 26 kg m⁻² (range 18-36 kg m⁻²), were included. On average, all formulae slightly overestimated GFR, as follows (in ml min⁻¹  1.73 m⁻²: CG +0.05 [95% confidence interval (CI) -28 to +28]; CG with IBW +0.03 (95% CI -20 to +20); MDRD +9 (95% CI -16 to +34); and CKD-EPI +5 (95% CI -20 to +29). They classified kidney disease correctly in 68.8% (CG), 75% (CG with IBW), 43.8% (MDRD) and 68.8% (CKD-EPI) of the participants, respectively.

CONCLUSIONS

The CG, CG with IBW, MDRD and CKD-EPI formulae estimate the mean GFR of a population rather well. In individual cases, all formulae may misclassify kidney disease by one stage.

Variability of glomerular filtration rate estimation equations in elderly Chinese patients with chronic kidney disease

Background

Chronic kidney disease (CKD) is recognized worldwide as a public health problem, and its prevalence increases as the population ages. However, the applicability of formulas for estimating the glomerular filtration rate (GFR) based on serum creatinine (SC) levels in elderly Chinese patients with CKD is limited.

Materials and methods

Based on values obtained with the technetium-99m diethylenetriaminepentaacetic acid (^99mTc-DTPA) renal dynamic imaging method, 319 elderly Chinese patients with CKD were enrolled in this study. Serum creatinine was determined by the enzymatic method. The GFR was estimated using the Cockroft–Gault (CG) equation, the Modification of Diet in Renal Disease (MDRD) equations, the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation, the Jelliffe-1973 equation, and the Hull equation.

Results

The median of difference ranged from −0.3–4.3 mL/min/1.73 m². The interquartile range (IQR) of differences ranged from 13.9–17.6 mL/min/1.73 m². Accuracy with a deviation less than 15% ranged from 27.6%–32.9%. Accuracy with a deviation less than 30% ranged from 53.6%–57.7%. Accuracy with a deviation less than 50% ranged from 74.9%–81.5%. None of the equations had accuracy up to the 70% level with a deviation less than 30% from the standard glomerular filtration rate (sGFR). Bland–Altman analysis demonstrated that the mean difference ranged from −3.0–2.4 mL/min/1.73 m². However, the agreement limits of all the equations, except the CG equation, exceeded the prior acceptable tolerances defined as 60 mL/min/1.73 m². When the overall performance and accuracy were compared in different stages of CKD, GFR estimated using the CG equation showed promising results.

Conclusions

Our study indicated that none of these equations were suitable for estimating GFR in the elderly Chinese population investigated. At present, based on overall performance, as well as performance in different CKD stages, the CG equation may be the most accurate for estimating GFR in elderly Chinese patients with CKD.

[Assessment of renal function in elderly after eighty years: Cockroft and Gault or Modification of diet in renal disease equation?]

Assessment of renal function is essential in the management of hospitalised patients, particularly in geriatric practice. Impairment of renal function is common in the elderly, aged of 80 years and over, and should be taken into account before prescribing drugs eliminated through the kidneys or performing investigations requiring iodine injection. Renal failure is also a predictor of mortality. In clinical practice, creatinine-based equations are recommended to assess kidney function. The most widely used equations are the Cockroft and Gault (CG) and the simplified Modification of diet in renal disease (MDRD) formulas. The former estimates the clearance of creatinine in millilitres per minute, the latter estimates the glomerular filtration rate in millilitres per minute per 1.73 m(2). In 2002, the French high authority for health recommended the use of the CG formula, but no recommendation was given for the elderly. In the literature, no study has compared CG and MDRD formulas with a reference method in this very old population. In the octogenarians, two studies have compared these formulas with the creatinine clearance calculated on the basis of a 24-hour urine collection and four studies have compared the formulas head to head. All these studies showed that the results obtained with the MDRD formula are higher from 10 to 30 mL/min/1.73 m(2) than the results obtained with the CG formula. Studies simulating drug prescription showed that the use of the MDRD formula would lead to a risk of drug over dosage in 20 to 36% of the elderly. Also, two studies have suggested that only creatinine clearance measured by the CG formula is a predictor of mortality in the very old population. In conclusion, in the octogenarian, none of these two formulas is ideal. However, based on the results of studies targeted to this elderly population, the best solution seems to be the use of the CG formula expecting new methods of evaluation of renal function.