Approach to hypertension diagnosis
It is important to diagnose the cause of hypertension and treat it if it is significant, but equally important to avoid diagnosing or labeling a patient as hypertensive when pressures are normal or transiently elevated. Overdiagnosis leads to unnecessary and expensive tests, and false labeling may adversely affect the subject’s application for work or life insurance.
A diagnostic evaluation is undertaken in children whose blood pressures are repeatedly above the 95th percentile. Diagnosis is approached by knowing the causes of hypertension (Tables 22-22, 22-23, and 22-24) and relating these to findings ascertained from a complete history and physical examination (Tables 22-25 and 22-26) and from basic laboratory tests (Table 22-27). Most of the common causes of hypertension will usually be evident after this evaluation and can be addressed as appropriate. If no cause is discovered, and if blood pressure remains near the 95th percentile, the child is observed at 3- to 6-month intervals. Mild hypertension in children does not require treatment, and elaborate studies to identify its cause are not warranted. A schema for diagnosis is given in
In children with more severe hypertension, the decision to proceed with further testing is influenced by several factors. The younger the child with significant hypertension or the higher the blood pressure, the more likely there is to be a correctable cause, and thus, further investigations should be pursued. If the child is markedly overweight, obesity is the likely cause. If there is a strong family history of essential hypertension, particularly in an adolescent patient, there is less need to look for another cause.
The more intensive investigations listed in
Table 22-28are used to diagnose renal and endocrine abnormalities, including tumors.
MINERALOCORTICOIDS Patients with aldosterone-secreting tumors or hyperplasia of the adrenals may develop hypertension. This is usually associated with hypernatremia, hypokalemia, metabolic alkalosis, increased plasma volume, a low and fixed plasma renin level, and increased aldosterone secretion rates. Serum electrolytes provide a fairly good screening test for this disorder, and they can be followed by measuring peripheral renin levels after 2 hours in the erect position. Persistently low renin levels then indicate the need for the more time-consuming and expensive measurements of aldosterone concentrations or secretion rates as well as tests to determine if aldosterone can be suppressed by giving a high salt intake and dexamethasone. Low renin activity does not prove mineralocorticoid excess because renin is low in about 20% of patients with essential hypertension.
There may be hypertension in adrenogenital syndromes because of 11β- and 17α-hydroxylase deficiencies. The former tend to have virilization and hyperkalemia with hyponatremia; the latter often have hypokalemic alkalosis. The hypertension is associated with increased fluid and sodium retention caused by overproduction of desoxycorticosterone. There are also hypertensive patients with overproduction of 18-hydroxydesoxycorticosterone.
GLUCOCORTICOIDS Blood pressure should be checked frequently in those taking high dosages of steroids. Hypertension occurs in Cushing syndrome. These patients usually have the typical cushingoid facies, buffalo hump, obesity, striae, hyperglycemia, and polycythemia; thus, routine measurements of 17-hydroxycorticosteroids or urinary free cortisol in an otherwise asymptomatic hypertensive patient without cushingoid features are not justified.
SEX HORMONES Girls taking oral contraceptives can develop hypertension, but if the agent is stopped, the pressure usually falls in 2 to 3 months. Testosterone administration may also cause blood pressure to rise. Preeclampsia should always be considered in girls of childbearing age.
RENAL DISORDERS Any type of renal parenchymal or vascular disease can cause hypertension. About 80% of secondary hypertension is caused by renal disease, four-fifths of which is related to renal anomalies and renal parenchymal disease and the rest to renal vascular abnormalities. Renal anomalies and parenchymal disease are diagnosed by renal ultrasound and DMSA scan. Renovascular disease may be detected by renal Doppler ultrasound, by magnetic resonance imaging, or by renal isotope scans with labeled MAG3 to show the relative distribution of blood flow to each kidney. The greatest sensitivity and specificity appear if these scans are done after giving captopril. These tests depend on differences between the two sides and so are of less value if there is bilateral renal artery stenosis. All these tests are 90 to 95% sensitive and 95% specific in detecting renal artery stenosis in adults, but there are few studies in children. In children, unlike adults, arterial lesions are more common in branch arteries than in the renal artery and are thus more difficult to detect.
Plasma renin may be measured before the patient gets out of bed in the morning, again after he or she has been erect for 2 hours, and perhaps again after institution of a low-sodium diet; each institution has its own method of doing these tests and its own standard. The captopril test is useful for evaluating renovascular disease. The patient, on a normal salt intake and on no antihypertensive drugs, has blood pressure and blood for plasma renin activity (PRA) measured after sitting quietly for 30 minutes and then 1 hour after being given captopril 0.3 mg/kg. Renovascular disease is indicated by stimulated PRA of 12 ng/mL/h plus an absolute increase in PRA of 10 ng/mL/h or more plus a percentage increase in PRA over 150%. Aldosterone may also be measured. Finally, renal vein renin may be measured at catheterization, and renal arteriography might be done; intraarterial digital subtraction angiography gives excellent images with low amounts of contrast material. Because these are the most invasive and the most expensive steps, they should not be done without good cause or before consultation with experts in the field.
Figure 22-89. Flow chart to show how to manage a child with arterial hypertension. The boxes that indicate the need for basic and extended evaluation refer to Tables 22-27 and 22-28 in conjunction with Tables 22-23 to
MODERATE AND SEVERE HYPERTENSION
Moderate and severe hypertension includes those with pressures above the 99th percentile. Severity is defined by the features listed inTable 22-29, and those with severe hypertension should be admitted to hospital. They may even need to have their blood pressures lowered before investigations to prevent serious complications (