Cystatin C Medication-Driven Changes: What Drugs Raise or Lower Your Results

What cystatin C measures

Cystatin C is a protein measured in blood to help estimate glomerular filtration rate, or eGFR. It is useful when creatinine is difficult to interpret and provides another way to estimate filtration. Your clinician may combine both blood markers and assess urine albumin for a fuller picture. MedlinePlus GFR testing.

Use the reference interval printed by the testing laboratory. A cystatin C concentration in mg/L and an eGFR in mL/min/1.73 m² are different results. A small movement in the protein concentration should not be converted into a diagnosis, a medication change or a promised longevity benefit on its own.

NIDDK identifies steroid exposure, thyroid dysfunction, inflammation and adiposity as factors that can influence cystatin C apart from GFR. Creatinine has its own limitations, including effects of muscle mass. Neither marker is automatically the correct one whenever the two disagree. NIDDK measurement limitations.

Which medicines can change the result?

The sections below explain the relevant studies and follow-up questions for each treatment.

Systemic steroids: the clearest medication-related concern

A 2026 observational study by Russel and colleagues evaluated 5,595 adults with cystatin C testing and iohexol-based measured GFR. Systemic glucocorticoid use was associated with higher cystatin C after accounting for measured filtration and other factors. Associations with opioids and loop diuretics were smaller. The combined creatinine-cystatin C equation was less biased than either marker alone in those medication groups. Record the steroid dose and timing when interpreting the result. Russel et al., 2026.

Experimental work in rats also found that dexamethasone increased cystatin C production without reducing inulin-measured GFR. This animal experiment examined the mechanism behind the change. Experimental corticosteroid study.

Tell the ordering clinician about the steroid, dose, route and dates. Do not stop a prescribed steroid to obtain a different test result. The clinician can decide whether another marker, repeat testing or measured GFR would change management.

Thyroid disease: direction matters

In a prospective series of 22 patients, cystatin C was lower during hypothyroidism and rose after levothyroxine restored thyroid hormone levels. It was higher during hyperthyroidism and fell after treatment. Creatinine moved in the opposite direction. The series included nine hypothyroid and 13 hyperthyroid patients. Fricker et al., 2003.

A cystatin C rise after treating hypothyroidism therefore does not, by itself, demonstrate worsening kidney filtration. Conversely, a low result during untreated hypothyroidism is not enough to establish normal kidneys. Thyroid treatment should follow the patient's thyroid assessment, not an attempt to reach a cystatin C target.

Testosterone and changes in muscle mass

A retrospective single-center study of 227 male athletes reporting testosterone use compared creatinine and cystatin C across body-composition groups. This observational study examined how the two markers relate across body-composition groups. A clinical assessment can distinguish changes in creatinine production from changes in kidney function. Testosterone and muscle-hypertrophy study.

TRAVERSE addressed a different question: cardiovascular safety of testosterone gel in 5,246 men with hypogonadism and existing or elevated cardiovascular risk. Acute kidney injury was reported more often in the testosterone group. Include changes in kidney tests in the treatment review rather than attributing them automatically to muscle gain. TRAVERSE primary publication.

SGLT2 inhibitors and GLP-1 treatment

KDIGO notes that a reversible eGFR decrease after starting an SGLT2 inhibitor is generally not, by itself, a reason to discontinue treatment. This does not mean every decline is harmless or that symptoms of dehydration or acute illness can be ignored. KDIGO 2024, practice point 3.7.3.

DAPA-CKD randomized 4,304 people with albuminuric CKD to dapagliflozin or placebo. It demonstrated fewer major kidney/cardiovascular outcome events in the dapagliflozin group, with benefit in participants with and without type 2 diabetes. Use these kidney-outcome findings alongside the individual's laboratory trend and clinical assessment. DAPA-CKD.

FLOW randomized 3,533 people with type 2 diabetes and CKD to semaglutide or placebo and found a lower risk of its major kidney-disease composite outcome with semaglutide. The FLOW population had both diabetes and CKD. When interpreting results during weight-loss treatment, account for body-composition changes and the person's kidney history. FLOW.

Which eGFR equation should the report use?

NIDDK lists three race-free adult CKD-EPI options: the 2021 creatinine equation, the 2021 combined creatinine-cystatin C equation and the 2012 cystatin C-only equation. The 2012 cystatin C-only equation is not an obsolete race-based formula. Combining markers often improves accuracy, while a strong non-GFR influence on one marker may change which estimate is most useful. NIDDK adult equations.

When a result is near a medication's dosing threshold, the prescriber or pharmacist should review the specific label, the method used to estimate kidney function and whether body-surface-area adjustment matters. NIDDK recommends considering the combined equation in such situations. Do not substitute a cystatin C number directly into a dose rule based on another measurement. NIDDK drug-dosing guidance.

What to bring to a results review

Bring the report with its units and equation, previous kidney results, all medicines and supplements, recent dose changes, thyroid results if relevant, and information about recent illness or substantial weight changes. Ask whether the discrepancy changes the treatment decision and which follow-up test would resolve it.

CKD requires evidence of chronicity over at least three months. Prior records, imaging or other findings may establish this; it is not always necessary to wait for two new blood draws. A sudden abnormal result still warrants timely assessment. KDIGO 2024, section 1.1.3.

Follow the laboratory's preparation instructions for the tests actually ordered. Do not pause medicines or delay an urgent assessment to satisfy an arbitrary retesting interval. MedlinePlus GFR testing.

References

1. MedlinePlus: Glomerular filtration rate testing.
2. NIDDK: Clinical measurements and eGFR accuracy.
3. Russel et al. Medications influencing serum cystatin C independent of measured GFR. 2026.
4. Corticosteroids and cystatin C production, experimental rat study. 2019.
5. Fricker et al. Thyroid dysfunction and serum cystatin C. 2003.
6. Creatinine and cystatin C in men with testosterone-induced muscle hypertrophy. 2024.
7. Lincoff et al. TRAVERSE testosterone cardiovascular-safety trial. 2023.
8. KDIGO: Clinical Practice Guideline for Evaluation and Management of CKD. 2024.
9. Heerspink et al. DAPA-CKD randomized trial. 2020.
10. Perkovic et al. FLOW randomized trial. 2024.
11. NIDDK: eGFR equations for adults.
12. NIDDK: Drug dosing in adults with CKD.