What is the likely cause of chronic hyponatremia (low sodium levels), hypochloremia (low chloride levels), and hypoglycemia (low glucose levels) in a 73-year-old male with hypertension (HTN), hyperlipidemia (HLD), chronic obstructive pulmonary disease (COPD), benign prostatic hyperplasia (BPH), depression, and morbid obesity, who is taking Lisinopril (lisinopril)-Hydrochlorothiazide (HCTZ)?

From the Guidelines

I strongly recommend ordering serum osmolality, urine osmolality, and urine sodium to evaluate this patient's chronic hyponatremia, as the patient's low sodium and chloride levels, with a history of similar hyponatremia, warrant further investigation. The patient's lab results show low sodium (126) and chloride (89) levels, with a history of similar hyponatremia (121-129 range) in previous labs, which suggests a chronic condition. The lisinopril-HCTZ is a likely culprit, as thiazide diuretics, such as hydrochlorothiazide, are a common cause of hyponatremia, especially in elderly patients, as noted in the 2022 AHA/ACC/HFSA guideline for the management of heart failure 1.

The patient's medication regimen, including lisinopril-HCTZ, should be carefully evaluated, as thiazide diuretics can inhibit reabsorption of sodium or chloride at the distal convoluting tubule, leading to hyponatremia 1. Other possibilities include SIADH, which can be associated with certain medications, including antidepressants, or hypovolemic hyponatremia from reduced intake. The low glucose (68) may indeed be due to fasting before the lab draw but should be monitored. The slightly elevated alkaline phosphatase (124) is likely not clinically significant but could be tracked on future labs.

When messaging your attending, emphasize the chronic nature of the hyponatremia, the potential relationship to the patient's medications, and your plan to determine the specific etiology through additional testing. Consider discussing whether medication adjustment (particularly the HCTZ component) might be appropriate depending on the severity of symptoms and test results. Key points to discuss include:

• The patient's chronic hyponatremia and its potential causes
• The role of thiazide diuretics, such as HCTZ, in causing hyponatremia 1
• The need for further testing, including serum osmolality, urine osmolality, and urine sodium, to determine the underlying etiology
• The potential for medication adjustment to address the hyponatremia and prevent further complications.

From the FDA Drug Label

CLINICAL PHARMACOLOGY Hydrochlorothiazide blocks the reabsorption of sodium and chloride ions, and it thereby increases the quantity of sodium traversing the distal tubule and the volume of water excreted. With continued use of hydrochlorothiazide and depletion of sodium, compensatory mechanisms tend to increase this exchange and may produce excessive loss of potassium, hydrogen and chloride ions.

The patient's low sodium and chloride levels may be related to the use of hydrochlorothiazide, as it increases the excretion of these ions.

• Key points:
  • Hydrochlorothiazide can cause depletion of sodium and chloride ions.
  • The patient's lab results show low sodium (126) and low chloride (89) levels.
  • The patient is taking lisinopril-hctz, which contains hydrochlorothiazide. Considering the patient's lab results and medication use, it is possible that the hydrochlorothiazide is contributing to the low sodium and chloride levels. Next steps:
• Order serum osmolality, urine osmolality, and urine sodium to further evaluate the patient's electrolyte imbalance.
• Consider consulting with the attending physician to discuss the patient's lab results and potential adjustments to their medication regimen 2.

From the Research

Abnormal Lab Results

The patient's lab results show low sodium (126), low chloride (89), and low glucose (68) levels, with slightly elevated alkaline phosphatase (124) levels.

Possible Causes of Hyponatremia

• Chronic hyponatremia may be due to the patient's lisinopril-hctz use, as hydrochlorothiazide (hctz) can cause hyponatremia 3
• Reduced salt intake due to cautiousness about hypertension may also contribute to hyponatremia
• The patient's low glucose level may be due to not having breakfast before the clinic visit

Evaluation of Hyponatremia

• Measuring serum osmolality, urine sodium concentration, and urine osmolality can help differentiate among possible causes of hyponatremia 3, 4, 5
• Evaluation of hyponatremia relies on clinical assessment and estimation of serum sodium, urine electrolytes, and serum and urine osmolality 6
• Point-of-care ultrasonography can be an important adjunct to physical assessment in estimating volume status 6

Management of Hyponatremia

• Hyponatremia should be corrected at a rate similar to that at which it developed 3, 4
• When symptoms are mild, hyponatremia should be managed conservatively, with therapy aimed at removing the offending cause 3
• When symptoms are severe, therapy should be aimed at more aggressive correction of the serum sodium concentration, typically with intravenous therapy in the inpatient setting 4

Next Steps

• Ordering serum osmolality, urine osmolality, and urine sodium tests may be necessary to further evaluate the patient's hyponatremia 3, 4, 5
• Consulting with the attending physician to discuss the patient's lab results and possible next steps is recommended