To the Editor,

We read with interest the study by Cases Amenós et al about the prevalence of chronic renal failure (CRF) in patients with or at a high risk of cardiovascular disease. The authors used the data from the MULTIRISC study1 to carry out an epidemiological, cross-sectional multicenter study in outpatient clinics belonging to cardiology, internal medicine and endocrinology departments. The patients were older than 18 years of age and with a high cardiovascular risk (SCORE [Systematic Coronary Risk Evaluation] >5% or diabetes mellitus or concomitant clinical disease). CRF was defined as an estimated glomerular filtration rate (MDRD [Modification of Diet in Renal Disease formula]) <60 mL/min/1.73 m2; established CRF was defined if, in addition, the serum creatinine was ≥1.3 mg/dL in men or ≥1.2 mg/dL in women, and occult CRF when the creatinine figures were lower.

The study sample comprised 2608 patients, of whom 62.7% did not have CRF, 18.9% had established CRF, and 18.4% had occult CRF. As was to be expected, when the clinical profile of the patients was compared according to whether or not they had CRF, those with CRF had more risk factors and associated vascular disease.

The clinical benefit of calculating the glomerular filtration rate is unquestionable, both to diagnose CRF and to adjust the doses of certain drugs. Moreover, patients with CRF are known to have a worse clinical profile, a greater cardiovascular risk and, consequently, a worse prognosis. Likewise, it is not uncommon for this population to be under-treated and to undergo fewer diagnostic tests, which just worsens the situation even more.2 Nevertheless, it should not be forgotten that the glomerular filtration rate is a continuous variable and a cut-off point of 60 mL/min/1.73 m2 is still arbitrary. Is there really such a difference in prognosis according to whether a patient has a glomerular filtration rate of 61 or 59 mL/min/1.73 m2?

A recent study involving 2024 patients with chronic ischemic heart disease and hypertension analyzed possible differences in the clinical profile and control of risk factors according to the glomerular filtration rate (≥60 vs <60 mL/min/1.73 m2) or according to serum creatinine figures (≥1.3/1.2 in men vs <1.3/1.2 mg/dL in women) and a glomerular filtration rate <60 mL/min/1.73 m2 vs creatinine ≥1.3/1.2 mg/dL, respectively.3 The results of this study, as well as demonstrating that approximately one third of the patients had CRF, also detected that the patients with CRF, independently of whether this was determined from the glomerular filtration rate or serum creatinine figures, had more risk factors, more organ damage and worse blood pressure control. However, the results also showed that the risk profile and blood pressure control did not vary according to whether the glomerular filtration rate was <60 mL/ min/1.73 m2 or the creatinine was ≥1.3/1.2 mg/dL (men/women), which indicates that these two parameters are identifying the same group of patients. Furthermore, it should be recalled that the measurement of either the glomerular filtration rate or serum creatinine can be affected under certain circumstances, so that just one single determination at a particular moment would seem inadequate.

Consequently, in view of these findings, the first point to consider is that greater importance should be given to the early detection of CRF, however mild it may be, as we are dealing with very high risk populations.4 Additionally, all patients with a creatinine ≥1.3/1.2 mg/dL (men/ women) should be considered as very high risk patients, since they already have CRF, though in fact many physicians fail to identify a creatinine of 1.3 mg/dL in a man as renal disease. Finally, in patients with normal creatinine figures, it should be obligatory to calculate the glomerular filtration rate, as they could have occult CRF, especially those patients who have several associated risk factors, concomitant vascular disease or poor blood pressure control.