Which tests can diagnose hidden kidney disease?

This study evaluated the rate of unrevealed (occult) chronic kidney disease (CKD) and the markers that can predict it in patients with high blood pressure (hypertension) and no diabetes. 

CKD (the progressive loss of kidney function) is frequent in persons with hypertension. CKD is also considered a high risk factor for cardiovascular disease, heart failure, total loss of kidney function and death. In patients with hypertension serum creatinine (a substance produced by the muscles eliminated unchanged by kidneys) levels and urine dipstick (a test strip used to determine changes of several parameters of patients’ urine) are recommended to diagnose CKD. However, these tests may miss hidden (occult) CKD (CKD that has been missed by regular serum creatinine and urine dipstick) CKD. Albumin-to-creatinine ratio or ACR (a test that determines the presence of low levels of proteins in the urine) and cystatin C or cysC (a marker of kidney function) are more precise tests of kidney function and can detect even occult CKD. This study aimed to evaluate the frequency of occult CKD in patients with hypertension.

This study included 2825 hypertensive patients without diabetes from 2 surveys that took part between 1988 and 1994 (n=2088) and 1999-2002 (n=737), respectively. Occult CKD was defined as an estimated glomerular filtration rate or eGFR (a test that checks how well the kidneys are working by measuring the amount of blood filtered by the kidneys each minute) by cystatin C of less than 60ml/min per 1.73m2 and/or by ACR of at least 30mg/g.

The results showed that 25% of the patients from the 1988-1994 group and 22% in the 1999-2002 group had occult CKD. In the 1988-1994 group, 13% non-diabetic hypertensive patients had occult CKD by ACR only, 8% by cysC only and 3% by both markers. Also, one third of the patients with occult CKD in the 1988-1994 group and over one quarter in the 1999-2002 group were 65 years or older. In both surveys, occult CKD was almost fully detected by ACR in persons younger than 45 years. The rate of occult CKD and the predictive markers also varied by race. Black patients and Mexican-Americans were more likely to have occult CKD detected by ACR only or ACR and cysC, while cysC only was more likely to detect occult CKD in white patients.

In conclusion, this study showed that the currently available tests for the detection of CKD for patients with hypertension may fail to identify all the cases. These cases can be identified by cystatin C, ACR or both, the test depending on the age and race of the patients. 

Future studies are needed to evaluate the potential benefits of introducing these tests in the current practice for the screening of CKD among hypertensive patients.

Ask your doctor about CKD and all the tests that could diagnose it.