Tests
1st tests to order
urinalysis
Test
Proteinuria indicates nephropathy is present.
Increased specific gravity may point to prerenal causes of decreased eGFR.
Urinary leukocytes, bacteria, and nitrites indicate urinary tract infection.
After the initial screen, urinalysis is not needed unless there is a specific indication (e.g., unexpected rapid decline in renal function, symptoms of urinary tract infection).
Result
proteinuria
urinary albumin to creatinine ratio (ACR)
Test
ACR on a first-void spot urine specimen is the preferred test; a random spot urine specimen is an acceptable alternative.[49]
To confirm moderately increased albuminuria (previously known as microalbuminuria) or severely increased albuminuria (previously known as macroalbuminuria), 2 of 3 specimens collected within 3-6 months should be abnormal.[1]
Exercise within 24 hours of specimen collection, infection, fever, congestive heart failure, significant hyperglycemia or hypertension, and menstruation may increase urinary ACR independently of kidney damage.[1]
Result
moderately increased albuminuria: 30-299 mg/g; severely increased albuminuria: ≥300 mg/g
serum creatinine with GFR estimation
Test
A 2021 Task Force convened by the National Kidney Foundation and the American Society of Nephrology recommended the adoption of the new Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) creatinine equation (2021) that estimates kidney function using creatinine, age, and sex, but no race variable (eGFRcr).[50] EBMCalc: glomerular filtration rate estimation (eGFR) by CKD-EPI equation with creatinine, without race (2021) Opens in new window This replaces the original CKD-EPI equation, which was previously widely used to estimate kidney function and contained an adjustment for black race.[50]
Result
eGFR may be elevated to normal in CKD stages 1-2 (≥60 mL/minute/1.73 m²), and reduced in CKD stages 3-5 (<60 mL/minute/1.73 m²)
kidney ultrasound
Test
Kidney size may initially be large if diabetes is uncontrolled, but usually normal once DKD supervenes.[52]
Ultrasound is important to exclude other causes of renal impairment in diabetic patients, such as obstruction, infection, cysts, or mass. Pyelonephritis may show as swelling of the parenchyma.[37]
Result
normal-to-large kidneys with increased echogenicity; may show hydronephrosis if vesiculopathy and/or obstruction is superimposed
Tests to consider
cystatin C with GFR estimation
Test
Cystatin C is an endogenous filtration marker biomarker that is increasingly being used as an alternative (or in addition) to creatinine to estimate renal function in clinical practice; it displays less variation due to muscle mass than creatinine and offers greater accuracy of GFR estimation, which improves the relationship between eGFR and subsequent risk of chronic kidney disease (CKD)-related outcomes, such as cardiovascular death and end-stage renal failure.[51] It is recommended for confirmatory testing of eGFR when more precise estimates are needed for clinical decision making; for example, to confirm the diagnosis of CKD when the creatinine-based eGFR is 45-60 mL/minute per 1.73 m² and there are no other features of CKD (such as albuminuria or radiologic abnormalities), or when individuals have prominent non-GFR determinants of serum creatinine that make creatinine-based estimation of GFR less accurate, e.g., high muscle mass, low muscle mass, creatine supplements, high animal protein diet, vegetarian diet, liver disease, or extreme frailty.[50] National efforts are under way in the US to facilitate increased, routine, and timely use of cystatin C.[50] Like the 2021 CKD-EPI creatinine equation, the 2021 CKD-EPI creatinine-cystatin C equation was developed without a term for race. It uses both creatinine and cystatin C and is more accurate, more closely approximates measured GFR, and supports better clinical decisions than either marker alone.[50]
Result
eGFR may be elevated to normal in CKD stages 1-2 (≥60 mL/minute/1.73 m²), and reduced in CKD stages 3-5 (<60 mL/minute/1.73 m²)
albumin excretion rate (AER)
Test
The AER is a timed (24-hour) urine collection for quantification of albuminuria.[47]
Timed collections are more burdensome and do not significantly improve accuracy compared with spot urine collection.[1]
Result
moderately increased albuminuria: 30-299 mg/24 hours; severely increased albuminuria: ≥300 mg/24 hours
CT abdomen
Test
CT scan is rarely warranted but may be useful if ultrasound is of poor quality in patients with obesity or if follow-up imaging is required to clarify pathology seen on ultrasound.[37]
Can exclude hydronephrosis, pyelonephritis, kidney stones, cysts, masses, renal cell carcinoma, and abnormal kidney ureter or bladder architecture.
Result
may show hydronephrosis; wedge-shaped areas of low attenuation; loss of the ability to distinguish the corticomedullary border; perinephric stranding; cysts; masses; stones
magnetic resonance angiography (MRA)
Test
MRA is not routinely used in the diagnosis of DKD but should be considered in patients who develop renal failure shortly after an ACE inhibitor has been started, or in patients with refractory hypertension who have failed to respond to 3 or 4 antihypertensives.[37] Previously, gadolinium was not given if the eGFR was <30 mL/minute/1.73 m²; however, newer gadolinium-based contrast agents (group II agents) are safe to use with low eGFR or in patients receiving maintenance dialysis.[53][54]
Result
to rule out renal artery stenosis
Doppler ultrasound
Test
Provides hemodynamic information about renal artery flow.[37]
Result
may show renal artery stenosis
kidney biopsy
Test
Considered in the following circumstances: in patients with type 1 diabetes who have had diabetes mellitus for a short period of time or who do not have retinopathy; if there is active urine sediment, rapid progression of proteinuria or nephrotic syndrome, or rapid decline in eGFR; or if there is evidence of another systemic disease.[36]
Result
mesangial expansion, fibrosis, Kimmelstiel-Wilson nodules
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