Causes of Increased BUN & Creatinine Unrelated to Kidney Function

Creatinine and blood urea nitrogen, or BUN, are both nitrogen-containing waste products generated by muscular activity. Many patients panic if lab results come back with elevated creatinine or BUN. This is understandable because these values can be red flags for kidney disease. A single abnormal lab value should never be cause for panic, however. Creatinine and BUN can be elevated because of dehydration, drug reactions, heart disease and surgery.

Drug Reactions

Angiotensin converting enzyme (ACE) inhibitors and cyclosporine both cause a mild elevation of creatinine and BUN. ACE inhibitors are prescribed to treat high blood pressure and cyclosporine is a common immunosuppressant used post-transplant. It is also given to treat very high urine protein and rheumatoid arthritis.

Patients often panic when they see their creatinine and BUN values increase after starting these drugs—particularly if they are already being treated for kidney disease—because they mistakenly believe their disease is getting worse.

While the lab increases due to these drugs are usually reversible, routine labs should be performed at regular intervals. There are rare instances in which long-term cyclosporine use has caused kidney toxicity which is not reversible.


Temporary increases in creatinine also occur after surgery involving the heart and arteries. In 2006, the journal Interactive Cardiovascular and Thoracic Surgery reported that researchers saw transient increases following abdominal aorta surgery. Likewise, similar transient increases following endovascular repair were reported in the Journal of Vascular Surgery. Endovascular repair is a type of surgery in which different parts of the body are accessed through vascular organs such as arteries.


Creatinine can also increase when patients have atherosclerosis. Atherosclerosis is synonymous with hardening of the arteries, a condition in which fatty deposits form along artery walls and eventually harden.

Mildly elevated serum creatinine is so common in patients with atherosclerosis that Dr. John Matts proposed that it be an independent disease marker. Writing in the Journal of Family Practice, Matts claims that elevated creatinine occurs in heart attack survivors who have normal blood pressure, normal weight, and who don't have pre-existing kidney or heart disease.

Lab Error

A a single out-of-range lab error is suggestive of lab error. Such mistakes should not be interpreted as evidence of kidney disease. It is very, very difficult for patients not to overreact to high creatinine values, particularly if the patient is already in frail health. Such values need to be considered within context, however.

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