# Situation: The public health nurse makes follow-up home visits to adults enrolled in the barangay registry for hypertension and diabetes. A 58-year-old man with type 2 diabetes has taken metformin for 6 years. His estimated glomerular filtration rate (eGFR) last month was 38 mL/min/1.73 m², unchanged from 6 months ago. Next week he is scheduled for coronary angiography, in which iodinated contrast dye is injected into an artery through a catheter. What should the nurse teach him about his metformin?

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> subject: Nursing Practice I — Community Health Nursing

## 문제

Situation: The public health nurse makes follow-up home visits to adults enrolled in the barangay registry for hypertension and diabetes.

A 58-year-old man with type 2 diabetes has taken metformin for 6 years. His estimated glomerular filtration rate (eGFR) last month was 38 mL/min/1.73 m², unchanged from 6 months ago. Next week he is scheduled for coronary angiography, in which iodinated contrast dye is injected into an artery through a catheter. What should the nurse teach him about his metformin?

## 보기

1. Hold it from the day of the procedure; resume after a kidney check **✔ 정답**
2. Stop it for good, since his eGFR is now below 45 mL/min/1.73 m²
3. Continue it, since his eGFR is still above 30 mL/min/1.73 m²
4. Continue it, and drink extra water before and after the procedure

**정답: 1**

## 해설

Two rules apply at once. An eGFR of 38 mL/min/1.73 m² is above the contraindication cut-off of 30, and a long-term user with stable kidney function continues metformin with closer monitoring, so it is not stopped for good. Separately, contrast injected into an artery through a catheter in a client with an eGFR of 30 to 60 is an indication to hold metformin at the time of or before the procedure; kidney function is rechecked about 48 hours later and metformin is resumed if it is stable, because contrast-induced kidney injury can lead to lactic acidosis.

## 심화 해설

The clinical decision here involves two separate safety principles that must be evaluated independently: the chronic-use kidney threshold for metformin, and the acute periprocedural risk when iodinated contrast is administered through an arterial catheter.

Chronic use and eGFR threshold

The client’s eGFR of 38 mL/min/1.73 m² is below 45 but still above the absolute contraindication cut-off of 30 mL/min/1.73 m². For a patient who has been on metformin for 6 years with stable kidney function, the appropriate long-term approach is to continue metformin with closer monitoring of renal function rather than discontinue it permanently. The eGFR has remained unchanged over 6 months, which supports ongoing use with surveillance. Therefore, stopping metformin for good is not indicated.

Periprocedural risk with iodinated contrast

The scheduled coronary angiography involves injection of iodinated contrast dye through an arterial catheter. In a client with an eGFR between 30 and 60 mL/min/1.73 m², contrast administration poses a risk of contrast-induced acute kidney injury. If kidney function declines acutely while metformin continues to be taken, the drug can accumulate and increase the risk of metformin-associated lactic acidosis, a rare but potentially fatal complication.

The standard precaution is to hold metformin on the day of the procedure or before it, then recheck kidney function approximately 48 hours afterward. If renal function remains stable, metformin can be safely resumed. This approach balances the low absolute risk of lactic acidosis against the need to avoid unnecessary permanent discontinuation of a beneficial glucose-lowering agent.

Watch out! Option 3 and option 4 both suggest continuing metformin through the procedure. While hydration is important for contrast nephropathy prevention, extra water intake alone does not eliminate the risk of metformin accumulation if contrast-induced kidney injury occurs. Holding the drug is the key protective measure.

Key point! The eGFR of 38 is not low enough to require permanent discontinuation, but it is low enough to trigger the periprocedural hold protocol when arterial contrast is planned.

| Clinical situation | Metformin action | Rationale |
| --- | --- | --- |
| eGFR 30–45, stable, no contrast exposure | Continue with closer monitoring | Above contraindication cut-off; benefit outweighs risk in stable chronic use |
| eGFR 30–60 and arterial iodinated contrast planned | Hold at or before procedure; recheck eGFR in 48 hours; resume if stable | Contrast-induced kidney injury can precipitate metformin-associated lactic acidosis |
| eGFR below 30 | Discontinue permanently | Contraindicated due to unacceptable lactic acidosis risk |

The NO-STOP trial examined whether continuing metformin during invasive coronary angiography is safe. In that study, diabetic patients undergoing coronary angiography with or without percutaneous coronary intervention were enrolled, and the primary endpoint focused on significant increases in lactate levels. The trial was designed as an open-label, prospective, multicentre, single-arm study, meaning it did not have a control group that held metformin. While the study explored the possibility that routine discontinuation may be unnecessary in selected patients, the current standard practice reflected in the question remains to hold metformin for patients with eGFR in the 30–60 range who are receiving arterial contrast. The study itself acknowledges that discontinuation is common practice due to the alleged risk of metformin-associated lactic acidosis, and it does not establish a new safety threshold that would override the periprocedural hold recommendation for this client’s eGFR category.

The correct teaching is to hold metformin from the day of the procedure and resume only after a kidney check confirms stable renal function.

## 임상 시나리오

Metformin Hold Before Contrast AngiographyPreventing Lactic Acidosis in CKD Stage 3
For a patient with an eGFR between 30 and 60 mL/min/1.73 m², hold metformin on the day of arterial iodinated contrast procedures such as coronary angiography.

Recheck kidney function approximately 48 hours after the procedure. Resume metformin only if the eGFR is stable compared to baseline.

CautionDo not permanently stop metformin solely for an eGFR of 38 mL/min/1.73 m² if the patient is a long-term user with stable renal function. The absolute contraindication threshold is 30 mL/min/1.73 m².

## 핵심 개념

- **Metformin-associated lactic acidosis** — A rare but life-threatening complication caused by metformin accumulation, particularly when renal function declines acutely.
- **Contrast-induced acute kidney injury** — An acute decline in renal function following iodinated contrast administration, especially in patients with pre-existing kidney impairment.
- **eGFR** — Estimated glomerular filtration rate; a measure of kidney function. Metformin is contraindicated below 30 mL/min/1.73 m².
- **Periprocedural hold** — Temporarily stopping a medication before a procedure to reduce risk, with resumption after reassessment.
- **Arterial contrast administration** — Injection of iodinated dye into an artery via catheter, which carries a higher risk of renal injury compared to intravenous use.

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