What laboratory tests are recommended for a young to middle-aged woman with fibromuscular dysplasia (FMD), hypertension, and potential kidney disease?

Laboratory Testing for Young to Middle-Aged Women with FMD, Hypertension, and Potential Kidney Disease

All patients with fibromuscular dysplasia and hypertension require comprehensive laboratory evaluation including serum creatinine with eGFR, urinary albumin-to-creatinine ratio, basic metabolic panel, and morning plasma aldosterone with plasma renin activity to screen for primary aldosteronism, which commonly coexists with resistant hypertension in FMD. 1, 2, 3

Essential Laboratory Tests (Required for All Patients)

Renal Function Assessment

• Serum creatinine with estimated glomerular filtration rate (eGFR) using race-free CKD-EPI equation to evaluate baseline kidney function and detect chronic kidney disease 1
• Urinary albumin-to-creatinine ratio (ACR) to identify early kidney damage and cardiovascular risk; moderate-to-severe CKD is defined as eGFR <60 mL/min/1.73 m² or albuminuria ≥30 mg/g (≥3 mg/mmol) 1
• If moderate-to-severe CKD is diagnosed, repeat serum creatinine, eGFR, and urine ACR at least annually 1

Basic Metabolic Panel

• Serum sodium, potassium, chloride, bicarbonate, glucose, blood urea nitrogen to detect electrolyte abnormalities and assess metabolic status 2, 4
• Hypokalemia is particularly important as it suggests primary aldosteronism, which frequently coexists with resistant hypertension 2, 5

Lipid Profile

• Fasting lipid panel (total cholesterol, LDL, HDL, triglycerides) for cardiovascular risk stratification 1, 4

Urinalysis

• Dipstick urinalysis to screen for proteinuria, hematuria, and other urinary abnormalities indicating kidney damage 1, 4

Critical Screening for Secondary Hypertension

Primary Aldosteronism Screening

• Morning plasma aldosterone and plasma renin activity (PRA) to calculate the aldosterone-to-renin ratio (ARR) 2, 3
• This is essential because resistant hypertension is common in FMD, and primary aldosteronism frequently coexists 2, 3
• An ARR >20 when serum aldosterone is >16 ng/dL and PRA is <0.6 ng/mL per hour suggests primary aldosteronism, particularly if the patient is taking an ACE inhibitor or ARB (these drugs elevate PRA, so suppressed renin increases sensitivity) 2
• Note that mineralocorticoid receptor antagonists raise aldosterone levels and β-blockers lower renin levels, diminishing interpretation 2

Additional Considerations

• Very elevated renin levels may raise suspicion for renovascular hypertension due to FMD 5, 6
• 24-hour urinary sodium or spot sodium-to-creatinine ratio may be helpful when evaluating renovascular hypertension to assess dietary sodium intake 6

Glucose Metabolism Assessment

• Fasting glucose or HbA1c to screen for diabetes mellitus, which significantly increases cardiovascular risk and lowers treatment thresholds 1, 7, 4
• Diabetes is an independent risk factor that places patients at increased cardiovascular risk regardless of other factors 7, 1

Additional Laboratory Tests Based on Clinical Context

If Pheochromocytoma Suspected

• Plasma metanephrines or 24-hour urinary metanephrines if clinical features suggest paraganglioma or pheochromocytoma (episodic hypertension, headaches, palpitations, sweating) 2

Thyroid Function

• Thyroid-stimulating hormone (TSH) as part of routine hypertension workup to exclude thyroid-related hypertension 1

Cardiac Biomarkers (Optional but Valuable)

• High-sensitivity cardiac troponin and/or NT-proBNP may be considered to assess hypertension-mediated organ damage in the heart 1
• These biomarkers help identify subclinical cardiac involvement and guide treatment intensity 1

Critical Pitfalls to Avoid

• Never delay aldosterone-renin screening in young women with FMD and resistant hypertension—primary aldosteronism coexists frequently and requires specific treatment 2, 3
• Monitor renal function carefully when initiating RAS blockers (ACE inhibitors/ARBs), particularly if bilateral renal artery stenosis is suspected, as acute renal failure can occur 5, 6
• Do not use captopril renal scintigraphy or selective renal vein renin measurements for screening—these are not recommended 3, 6
• Repeat eGFR and urine ACR annually if CKD is diagnosed to monitor progression 1

Frequency of Monitoring

• Initial comprehensive laboratory evaluation at diagnosis 1, 4
• Annual repeat of serum creatinine, eGFR, and urine ACR if moderate-to-severe CKD is present 1
• More frequent monitoring if starting or adjusting RAS blockers, particularly in bilateral disease 5, 6