Chronic kidney disease in Norwegian primary care: underdiagnosis and undertreatment — findings from the VISTAKID (Vestfold Investigation of Stage 3–5 Kidney Disease) study

Chronic kidney disease (CKD) is common yet frequently unrecognized in primary care. We aimed to quantify the burden of CKD stages 3–5 identified via routine general practice (GP) testing, compare characteristics of patients known vs unknown to nephrology, and estimate population prevalence to inform shared-care pathways. We assembled a laboratory cohort of adults whose serum creatinine tests were ordered by GPs in Vestfold between April 2010 and January 2021. Individuals with at least one eGFR < 60 mL/min/1.73 m2 were identified, and CKD stages 3–5 were confirmed according to KDIGO criteria (≥2 eGFR < 60 mL/min/1.73 m2 at least 90 days apart). eGFR was calculated using the CKD-EPI 2009 equation. Hospital registries were used to classify patients as known CKD (diagnosed and followed in nephrology) or unknown CKD (no nephrology diagnosis/follow-up). We compared demographics, CKD stage distribution, and use of laboratory tests related to CKD complications (e.g. acid–base, phosphate, iron indices, proteinuria). Among 18,355 individuals with ≥1 eGFR < 60 mL/min/1.73 m2, 13,480 met KDIGO criteria for CKD stages 3–5 (mean eGFR 48 mL/min/1.73 m2; mean age 77 years; 56% women). Of these, 1952 (15%) were known to nephrology, leaving 11,531 (≈85%) without a registered CKD diagnosis or nephrology follow-up. Disease severity differed by care status: stages 3b–5 accounted for 54% among known CKD vs 28% among unknown CKD. Testing patterns suggested underuse of key CKD complication assessments in primary care—particularly quantification of proteinuria and labs for metabolic acidosis, hyperphosphatemia, and iron status—whereas such tests were more common among patients followed in nephrology. The estimated cumulative period prevalence of CKD stages 3–5 in Vestfold was 3.7% over the study period. Across the study period, the vast majority of patients with laboratory-confirmed CKD stages 3–5 identified in primary care were not known to nephrology, indicating substantial gaps in diagnosis and risk stratification. Limited use of proteinuria testing and complication-focused laboratory assessments likely contributes to missed recognition and delayed treatment. Implementation priorities include systematic albuminuria measurement, streamlined decision support for GPs, and accessible specialist input (e-consults/virtual triage) to improve detection and management without overwhelming clinic capacity. • Recognition gap, quantified: County-wide, single-laboratory cohort with strict KDIGO confirmation linked to nephrology coding shows a large recognition gap (majority of stage 3–5 CKD not coded/known to nephrology) and a distinct stage-mix difference (higher 3b–5 among known cases). • Testing gap, measurable and actionable: Complication-oriented labs and proteinuria testing are used far less in primary care than in specialist care, defining clear quality-improvement targets (e.g., systematic U-ACR). • Triangulated with GP behavior: A multi-county GP survey aligns with the cohort—limited albuminuria testing, variable diagnostic thresholds, and low guideline familiarity—pinpointing practical levers (simple decision support and low-threshold e-consults). • Policy-relevant baseline: Provides a pre-implementation baseline for Norway’s new joint CKD guidance and generalizable indicators for gatekeeper primary-care systems.