Investigations

1st investigations to order

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Includes sodium, potassium, chloride, bicarbonate, BUN, creatinine, and glucose.

Serum creatinine alone is insufficient to determine CKD, and may be falsely low in conditions of low muscle mass, as in older or malnourished people, or patients with liver failure. 

Normal creatinine in men is 0.8 to 1.4 mg/dL, and in women 0.6 to 1.1 mg/dL. However, there is significant variation due to calibration methods between laboratories.[3]

Electrolyte abnormalities may indicate an underlying cause of CKD, such as tubular disorders.[1] Adaptations in acid excretion by the kidneys initially prevent a fall in serum bicarbonate concentration, but as GFR declines, metabolic acidosis develops.[1]

Result

elevated serum creatinine; electrolyte abnormalities

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A GFR estimating equation using serum creatinine is recommended for initial assessment.

Determines more accurately, by mathematical equations such as Cockcroft-Gault, the Modification of Diet in Renal Disease Formula, or the CKD EPI equation, the GFR and the severity and stage of CKD.[43]

Formulas have not been proven to be reliable estimators in patients with a GFR >59 mL/minute/1.73 m².[1][ Glomerular Filtration Rate Estimate by the IDMS-Traceable MDRD Study Equation ][ Glomerular Filtration Rate Estimate by CKD-EPI Equation ]

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<60 mL/minute/1.73 m²

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Warranted in specific circumstances when GFR estimates based on serum creatinine are thought to be inaccurate, such as in people with extremes of muscle mass (e.g., bodybuilders, people with muscle wasting disorders, older or malnourished people).[1][44]

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reduced muscle mass will lead to overestimation; increased muscle mass to underestimation of the GFR

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Screening test to determine for pathologic markers of kidney damage excreted in the urine.

Result

hematuria and/or proteinuria

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Classification of CKD requires quantification of urinary albumin as based on albumin excretion rate (AER) or albumin to creatining ration (ACR).[1] Moderately increased albuminuria is a risk factor for the development of progressive CKD and coronary artery disease associated with diabetes and hypertension. Indicated in patients with diabetes and CKD if there was no evidence of proteinuria on urine dipstick.[45]

Result

moderately increased (AER 30-300 mg/day; ACR 3-30 mg/mmol (30-300 mg/g)

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Helps to diagnose CKD if kidney atrophy is present and diagnoses obstruction with hydronephrosis or bladder retention.

Result

small kidney size; presence of obstruction/hydronephrosis; kidney stones

Investigations to consider

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Helps to determine pathologic diagnosis of CKD in glomerular nephrotic and nephritic syndromes, and in people with diabetes with atypical presentations such as rapidly progressive kidney failure. Also essential in determining whether pathologic lesions are due to infection (e.g., hepatitis B and C, syphilis, and streptococcal pharyngitis). Provides insight into treatment options based on severity or chronicity of scarring of glomeruli and interstitium.

Result

variable depending on etiology

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Nonspecific test that may aid in the detection of calcium-containing kidney stones, as medication and urate stones are not apparent on plain radiography.

Result

may reveal calcium-containing kidney stones

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Imaging test that is helpful to determine the presence or absence of kidney stones and confirms obstructive component. It is also helpful to further evaluate cystic lesions or mass lesions in the kidney. Intravenous contrast is used with caution in high-risk patients, such as those with CKD with a reduction in the estimated GFR <60 mL/minute, as it can cause acute kidney injury. Prophylaxis with intravenous normal saline may be indicated or considered in some patients.[46]

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may reveal kidney stones, renal masses, or cysts

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Imaging test that further characterizes mass lesions in the kidney, such as renal cell carcinoma.

Gadolinium-based MRI examinations have been associated with nephrogenic systemic fibrosis in patients with kidney disease. However, not all gadolinium-containing contrast agents have the same risk of nephrogenic systemic fibrosis, and the benefits of gadolinium-based MRI use may exceed its risk.[47] 

Result

may reveal mass lesions in the kidney

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