Abstract
Background: Cognitive dysfunction can occur in a significant proportion of patients with chronic kidney disease (CKD). Subclinical uremic encephalopathy (SUE) is defined as cognitive impairment (CI) greater than expected for normal aging and educational level. SUE is characterized by declining cognitive function that becomes irreversible if left untreated. However, there is no specific test to confirm the diagnosis of SUE.

Aim and Objectives: To determine the diagnostic accuracy of psychometric hepatic encephalopathy score (PHES) and critical flicker fusion frequency (CFFF) tests in SUE in CKD Stage 5 patients and to estimate the prevalence of CI among CKD patients.

Materials and Methods: It was a cross-sectional study conducted at a tertiary care center in Chennai, South India, during September 2022–October 2022, among 35 patients diagnosed with CKD Stage 5. All patients were subjected to MMSE (Mini-mental state examination), PHES test, and CFFF test consecutively and their scores were recorded. The collected data were analyzed with IBM SPSS Statistics for Windows, Version 29.0. The scores of PHES and CFFF were compared against MMSE and their diagnostic accuracy was tested using the receiver operating characteristics curve (ROC) along with sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy, and P < 0.05 was considered statistically significant.

Results: Of all 35 patients, 19 (54%) were males with a median age of 60 years. Fifteen patients (43%) were on hemodialysis. The prevalence of CI among CKD patients was 60%. CI was detected with MMSE in 21 patients (60%). Out of the 21 patients, 18 were positive with PHES (P < 0.01) and 19 were positive with CFFF (P < 0.05). PHES showed better sensitivity (90.9%), specificity (90.0%), PPV (90.9%), and NPV (90.0%) than CFFF, which showed a sensitivity of (89.7%), specificity (85.3%), PPV (86.8%), and NPV (87.5%). PHES was more accurate (accuracy – 90.5%) than CFFF (85.5%). 29 (83%) patients completed MMSE and 24 (69%) patients completed PHES, whereas all patients (100%) completed CFFF test. The average time taken in minutes to complete MMSE, PHES, and CFFF was 14.68 ± 2.02, 30.11 ± 4.13, and 5.48 ± 1.44 min, respectively. Cognitive function scores did not differ significantly with the duration of CKD and between patients with CKD receiving dialysis.

Conclusion: Both PHES and CFFF are effective in detecting impaired cognition and can be used as reliable tools in the diagnosis of SUE. Moreover, CFFF was less time-consuming and easier to complete, making it an ideal bedside test. The prevalence of CI among CKD patients was considerably high (60%). Hence, early detection and treatment would prevent patients from going into overt uremic encephalopathy where CI can become irreversible.

Key words: Chronic Kidney Disease; Cognition; Diagnostic Test Accuracy; Flicker Fusion; Uremic Encephalopathy