An 70-year-old male patient with uncontrolled hypertension has serum creatinine of 4.5, mild proteinuria. Renal ultrasound shows left kidney 9 cm and right kidney 7 cm in length {normal 10 cm). There was no obstruction. What is the next investigation of choice?
Correct Answer: Isotope renogram
Description: Ans: C (Isotope renogram) Ref: Harrison's Principles of Internal Medicine, 18th ednExplanation:Imaging Studies in Chronic Kidney DiseaseThe most useful imaging study is a Renal ultrasound.Advantages of Renal Ultrasoundo Verify the presence of two kidneyso Determine if they are symmetrico Provide an estimate of kidney sizeo Rule out renal masseso Evidence of obstruction.Since it takes time for kidneys to shrink as a result of chronic disease, the finding of bilaterally small kidneys supports the diagnosis of CKD of long-standing duration, with an irreversible component of scarring.If the kidney size is normal, it is possible that the renal disease is acute or subacute.The exceptions are diabetic nephropathy {where kidney size is increased at the onset of diabetic nephropathy before CKD with loss of GFR supervenes). Amyloidosis and HIV nephropathy, where kidney size may be normal in the face of CKD.Polycystic kidney disease that has reached some degree of renal failure will almost always present with enlarged kidneys with multiple cysts.A discrepancy >1 cm in kidney length suggests either a unilateral developmental abnormality or disease process or renovascular disease with arterial insufficiency affecting one kidney more than the other.The diagnosis of renovascular disease can be undertaken with different techniques, including Doppler sonography, nuclear medicine studies, or CT orMRI studies.If there is a suspicion of reflux nephropathy (recurrent childhood urinary tract infection, asymmetric renal size with scars on the renal poles), a voiding cystogram may be indicated.However, in most cases by the time the patient has CKD, the reflux has resolved, and even if still present, repair does not improve renal function.Radiographic contrast imaging studies are NOT particularly helpful in the investigation of CKD.Intravenous or intraarterial dye should be avoided where possible in the CKD patient, especially with diabetic nephropathy, because of the risk of radiographic contrast dye- induced renal failure.When unavoidable, appropriate precautionary measures include avoidance of hypovolemia at the time of contrast exposure, minimization of the dye load, and choice of radiographic contrast preparations with the least nephrotoxic potential.Additional measures thought to attenuate contrast-induced worsening of renal function include judicious administration of sodium bicarbonate-containing solutions and W-acetyl-cysteine.A retrograde pyelogram may be indicated if a high index of clinical suspicion for obstruction exists despite a negative finding on renal ultrasonography.Intravenous pyelography is not commonly performed, because of the potential for renal toxicity from the intravenous contrast; however, this procedure is often used to diagnose renal stones.A renal radionuclide scan can be used to screen for renal artery stenosis when performed with captopril administration; it also quantitates differential renal contribution to total glomerular filtration rate (GFR). However, radionuclide scans are unreliable in patients with a GFR of less than 30 mL/min/1.73 m2.Magnetic resonance angiography (MRA) is becoming more useful for the diagnosis of renal artery stenosis, although renal arteriography remains the criterion standard. However, MR! contrast is problematic in patients with existing chronic kidney disease (CKD) because they have a low, but potentially fatal, risk of developing nephrogenic systemic fibrosis.
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