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Jason Sina, Kwaku D Tawiah, Mitchell G Scott, Caroline E Franks, “Shaking” the Kidneys Up!, Clinical Chemistry, Volume 68, Issue 3, March 2022, Pages 481–482, https://doi.org/10.1093/clinchem/hvab221
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Case Presentation
A 48-year-old healthy-appearing white male with past medical history of nephrolithiasis and gout on daily Allopurinol presented to his physician for routine care. The physician noted a steady increase in the patient’s serum creatinine occurring over the past 3 years (Table 1). The patient’s most recent estimated glomerular filtration rate (eGFR) was calculated to be 57 mL/min/1.73 m2 (Stage G3a CKD), a decline of 10 mL/min/1.73 m2 in 3 years. Other laboratory values and renal ultrasound imaging were unremarkable.
| Analyte / Date . | September 2018 . | October 2020 . | December 2020 . | March 2021 . |
|---|---|---|---|---|
| Serum creatinine, mg/dL (Ref: 0.8–1.30 mg/dL) | 1.27 | 1.31 | 1.33 | 1.45 |
| eGFR, mL/min/1.73 m2 | 67 | 64 | 63 | 57 |
| Uric acid, mg/dL (Ref: 3.0–8.0 mg/dL) | 5.6 | 5.4 | N/A | 6.5 |
| Serum cystatin C, mg/L (Ref: 0.68–1.22 mg/L) | N/A | N/A | N/A | 0.90 |
| 24-h urine creatinine clearance, mL/min | N/A | N/A | N/A | 96 |
| Analyte / Date . | September 2018 . | October 2020 . | December 2020 . | March 2021 . |
|---|---|---|---|---|
| Serum creatinine, mg/dL (Ref: 0.8–1.30 mg/dL) | 1.27 | 1.31 | 1.33 | 1.45 |
| eGFR, mL/min/1.73 m2 | 67 | 64 | 63 | 57 |
| Uric acid, mg/dL (Ref: 3.0–8.0 mg/dL) | 5.6 | 5.4 | N/A | 6.5 |
| Serum cystatin C, mg/L (Ref: 0.68–1.22 mg/L) | N/A | N/A | N/A | 0.90 |
| 24-h urine creatinine clearance, mL/min | N/A | N/A | N/A | 96 |
| Analyte / Date . | September 2018 . | October 2020 . | December 2020 . | March 2021 . |
|---|---|---|---|---|
| Serum creatinine, mg/dL (Ref: 0.8–1.30 mg/dL) | 1.27 | 1.31 | 1.33 | 1.45 |
| eGFR, mL/min/1.73 m2 | 67 | 64 | 63 | 57 |
| Uric acid, mg/dL (Ref: 3.0–8.0 mg/dL) | 5.6 | 5.4 | N/A | 6.5 |
| Serum cystatin C, mg/L (Ref: 0.68–1.22 mg/L) | N/A | N/A | N/A | 0.90 |
| 24-h urine creatinine clearance, mL/min | N/A | N/A | N/A | 96 |
| Analyte / Date . | September 2018 . | October 2020 . | December 2020 . | March 2021 . |
|---|---|---|---|---|
| Serum creatinine, mg/dL (Ref: 0.8–1.30 mg/dL) | 1.27 | 1.31 | 1.33 | 1.45 |
| eGFR, mL/min/1.73 m2 | 67 | 64 | 63 | 57 |
| Uric acid, mg/dL (Ref: 3.0–8.0 mg/dL) | 5.6 | 5.4 | N/A | 6.5 |
| Serum cystatin C, mg/L (Ref: 0.68–1.22 mg/L) | N/A | N/A | N/A | 0.90 |
| 24-h urine creatinine clearance, mL/min | N/A | N/A | N/A | 96 |
Questions
What clinical characteristics should be considered when interpreting creatinine-based eGFR?
What diagnostic method would you recommend for further work-up?
The answers are below.
There is a proportional relationship between serum creatinine and lean body mass independent of GFR (1). Creatinine-based eGFR is less accurate in individuals with atypical muscle mass (e.g., amputees, bodybuilders). Cystatin C-based eGFR, on the other hand, is not impacted by muscle mass (1, 2). This patient was an avid weightlifter whose lean body mass increased with strenuous exercise and daily protein shakes. His cystatin C-based eGFR (CKD-EPI) was 94 ml/min/1.73 m2.
Author Contributions
All authors confirmed they have contributed to the intellectual content of this paper and have met the following 4 requirements: (a) significant contributions to the conception and design, acquisition of data, or analysis and interpretation of data; (b) drafting or revising the article for intellectual content; (c) final approval of the published article; and (d) agreement to be accountable for all aspects of the article thus ensuring that questions related to the accuracy or integrity of any part of the article are appropriately investigated and resolved.
Authors’ Disclosures or Potential Conflicts of Interest
Upon manuscript submission, all authors completed the author disclosure form. Disclosures and/or potential conflicts of interest:
Employment or Leadership
M.G. Scott, Clinical Chemistry, AACC.
Consultant or Advisory Role
None declared.
Stock Ownership
None declared.
Honoraria
None declared.
Research Funding
None declared.
Expert Testimony
None declared.
Patents
None declared.
References
