To the Editor,
In response to the letter of Barrios et al concerning our article published in the Revista Española de Cardiología,1 we wish to make the following comments.
The glomerular filtration rate (GFR) is indeed a continuous variable, but we do not agree that the criterion of 60 mL/min/1.73 m2 is an arbitrary value. This figure was based on criteria of morbidity and mortality employed by the American K/DOQI initiative in developing its classification of chronic kidney disease, and which was subsequently accepted internationally.
We coincide with these authors in their appreciation of the limitations of measuring creatinine, and thus of the estimated GFR (eGFR) using equations based on creatinine, as well as the need for 2 determinations, at least 3 months apart, to conclude that a patient has chronic renal failure (CRF). However, it is the simplest way to estimate the GFR, as recognized by nephrology societies as well as other scientific societies, such as the AHA.
Barrios et al cite a cross-sectional study of theirs from which they infer that creatinine is to be used if it is high and only eGFR if this is within the reference range to detect occult renal failure.
We believe this to be an excessive simplification: the risk of morbidity and mortality has been shown to increase as the GFR decreases, and the prevalence and severity of hypertension increases in parallel with the reduction in the eGFR.
The classification of chronic renal disease into different stages helps the physician to know what approach to take at any particular time. CRF is associated with various complications, such as anemia or alterations in bone and mineral metabolism, that need to be evaluated and treated.
The pharmacokinetics is altered in CRF. In the MULTIRISC study, we noted that the use of drugs that were contraindicated or unsuitable, eg, metformin or aldosterone antagonists, in patients with an eGFR <30 mL/min/1.73 m2 was not negligible. This was partly attributed to lack of recognition of the stage by the health care professionals. Finally, early referral to the nephrologist is associated with better survival.
Thus, for all these reasons, we believe that the eGFR should be determined in all patients, not just to categorize them as patients with a high cardiovascular risk, but also to classify them correctly, delay the disease progression, treat the complications derived from the CRF, avoid iatrogenic complications and, if necessary, refer the patient to the nephrologist.