Does a patient with a previous creatinine (serum creatinine) level above the old cutoff point of 87 and a current level of 127, below the new cutoff point of 129, have Chronic Kidney Disease (CKD)?

CKD Diagnosis: Serum Creatinine Changes with Laboratory Reference Range Updates

This patient has CKD regardless of the laboratory cutoff change, because CKD diagnosis is based on estimated GFR (eGFR) calculated from serum creatinine using validated equations—not on whether creatinine exceeds an arbitrary laboratory reference range. 1

Why Laboratory Cutoffs Are Irrelevant for CKD Diagnosis

The diagnosis of CKD requires either:

• eGFR <60 mL/min/1.73 m² persisting for ≥3 months, OR
• Albuminuria (UACR ≥30 mg/g) persisting for ≥3 months 1, 2

Laboratory reference ranges for creatinine (like your "cutoff of 129" or the previous "87") are simply statistical ranges for healthy populations and have no diagnostic value for CKD. 1 The critical error here is conflating a laboratory reference range with a diagnostic threshold for kidney disease.

The Correct Diagnostic Approach

Calculate eGFR using the CKD-EPI equation (not just looking at raw creatinine values):

• A creatinine of 121 μmol/L (1.37 mg/dL) three months ago likely corresponds to an eGFR well below 60 mL/min/1.73 m² depending on age, sex, and race 1
• A creatinine of 127 μmol/L (1.44 mg/dL) now represents either stable or worsening kidney function 1
• Both values are abnormal regardless of laboratory cutoffs 1, 2

The relationship between creatinine and GFR is non-linear—serum creatinine remains in the "normal range" until GFR drops below approximately 60 mL/min/1.73 m², meaning significant kidney disease can exist with creatinine values that laboratories report as "normal." 1, 3

Essential Next Steps

Immediately measure:

1. Urinary albumin-to-creatinine ratio (UACR) on a random spot urine sample 1, 2
2. Calculate eGFR using the CKD-EPI 2021 equation (available at nkdep.nih.gov) 1, 2
3. Review historical creatinine/eGFR values to confirm duration >3 months 2

If eGFR is 30-59 mL/min/1.73 m² (CKD Stage 3):

• Screen for CKD complications: complete metabolic panel, CBC, calcium, phosphate, intact PTH, 25-hydroxyvitamin D 2
• Monitor every 3-6 months depending on albuminuria level 2

If eGFR is <30 mL/min/1.73 m² (CKD Stage 4-5):

• Refer to nephrology immediately 1, 2

Common Pitfalls to Avoid

Never rely on serum creatinine alone or laboratory reference ranges to diagnose or exclude CKD—this leads to systematic underdiagnosis of kidney disease, particularly in elderly patients, women, and those with lower muscle mass. 1

Do not skip albuminuria testing—eGFR and UACR provide independent prognostic information for cardiovascular events, CKD progression, and mortality. 1, 2 Approximately 20-40% of CKD patients have reduced eGFR without albuminuria, representing a distinct phenotype. 1, 2

Biological variability in creatinine (reference change value of 14-17%) means small absolute rises on a background of elevated baseline creatinine may represent random variation rather than true progression, but this does not negate the underlying CKD diagnosis. 1