Obtain several sets of blood pressures on different days. Is the blood elevation an isolated phenomenon or is it real?

If the blood pressure is above the 99th % for age or the patient is symptomatic one may need to evaluate the child immediately.

Obtain a urinalysis.

Urine that is positive for blood and/or protein would indicate the presence of glomerulonephritis. A urine positive for white cells could indicate a urinary tract infection or the presence of interstitial disease. A fixed specific gravity of 1.010 could indicate chronic renal failure. A basic urine pH could indicate an acidification defect.

Obtain electrolytes, BUN and creatinine.

A low CO2 would indicate acidosis. An elevated chloride would indicate renal tubular disease causing the acidosis. A high CO2, low potassium, and a low chloride would indicate mineralocorticoid excess. An elevated potassium could be seen in renal failure and Type IV renal tubular acidosis. Renal failure would be seen with an elevated BUN, creatinine, and a low CO2.

The evaluation could be stopped here, if the patient is an obese adolescent with no other abnormalities present. 

Fasting lipid levels could also be drawn at this point.

A renal imaging study such as the ultrasound can be used to assess for gross renal abnormalities such as hypoplastic/dysplastic kidneys.

Renal artery disease may be sometimes suggested my one kidney significantly smaller than the other. A dilated collecting system could indicate obstructive uropathy and/or ureterovesical reflux. However, these conditions alone usually do not result in hypertension unless there is significant renal impairment.

End organ damage should be assessed, if hypertension is severe and long standing. 

An eye examination by an ophthalmologist may be preformed to assess for vessel damage. The heart may be evaluated by an ECG. An echocardiogram is more sensitive to detect early LVH. If not the primary cause of the hypertension, the kidneys may be assed by a protein/creatinine ratio in the urine or by the presence in increased levels of microalbumin in the urine.

If further evaluation is warranted, attempt a focused evaluation.

If renal parenchymal disease is suspected, a renal biopsy should be scheduled. If renal artery stenosis is suspected, a renal arteriogram with split renal vein renin levels may be performed. A pre and post captopril radionuclide scan may be performed. Renal vessels may also be studied using MRA. The arteriogram is the most invasive, but is the most conclusive. The stenosis may be dilated using this technique. All of these studies require a degree of cooperation and therefore may require sedation and/or general anesthesia in young children

If suggested by physical or laboratory findings, a 24 hour urine collection may be obtained looking for elevated catecholamine or mineralocorticoid excretion.

This is usually not helpful unless there are clinical suggestions of an underlying condition.