CBC, CMP
UA, Urine mic (check for eosinophils), casts, proteins
Uosm, UNa, UCr, UPEP with immunofixation
Posm, SPEP with immunofixation in proteinuric patients to evaluate for monoclonal gammopathy. Suspect this when there is a large protein-albumin gap.
Sr. Cortisol, TSH
Renal U/S, re: to r/o obstructive uropathy
Doppler imaging for RAS or RVT
ESR, ANA, C3, C4, CH50, c-ANCA, p-ANCA, RPR, anti-GM abs. Serum cryoglobulins, ASO titers
Eosinophiluria is seen in interstitial nephritis, atheroembolic renal disease, or prostatitis.
Hep-B, C, HIV
Cockcroft-Gault formula for creatinine clearance:
(140-age) x (IBW in Kg) x 0.85 (for women)/72 x Cr in mg/dL
This formula has the tendency to overestimate the GFR, particularly as renal function begins to worsen.
The Modification of diet in renal disease (MDRD) formulas can calculate the GFR and can take into account the BUN, albumin and race in addition to age and gender (http://mdrd.com). When the MDRD GFR is >60 mL/min/1.73 m2, CKD should not be diagnosed unless other evidence of renal damage (e.g., proteinuria) is present.
Sr. creatinine must be stable baseline, for urine protein:urine creatinine to be credible.
Protein >3 g/24 hr urine = nephrotic synd
Protein <3 g/24 hr urine, with RBC casts = nephritic synd
Spot urine protein mg: mg of urine creatinine ratio more practical alternative, provided the creatinine is stable. Both units must be same as this is a ratio.
Ratio >3.5 = nephrotic range proteinuria
Ratio < 0.25 is within normal limits.
If in mg:g; ratio <250 mg of urine protein/gm of urine creatinine.
Do 24-h urine protein collection if Sr. Cr is not stable baseline.
FENa = [(UNa x PCr) / (UCr x PNa)] x 100 . This equation is most useful with oliguric renal failure, but may be helpful in nonoliguric renal failure. Not valid if Pt is in nonoliguric ARF and/or in Pts have been exposed to loop diuretics in the previous day. The FeNa has limited utililty when ARF is superimposed on CKD. To calculate FeNa and FeUrea: urine sodium, urea, and creatinine can be obtained with simultaneous serum measurements.
Renal US: small kidneys <9 cm = chronic disease.
Large kidneys in DM, HIV, deposition disease, PKD.
Discrepancy in kidney size of >2 cm suggests unilateral renal artery stenosis with atrophy of the affected kidney.
Hydronephrosis = obstructive nephropathy. Retroperitoneal fibrosis can encase the ureters and pevent dilation despite the presence of an obstruction
Hematuria > 3 RBC/HPF = infectious, inflammatory or malignant processes in the urinary tract. Dysmorphic RBCs suggest a glomerular source of bleeding and seen usually with RBC casts formed within the tubules.
Positive dipstick for blood, no RBC in urine = hemolysis or rhabdomyolysis.
WBC in urine = infectious, inflammatory. UTI, pyelonephritis or abscess, or AIN.
IVU for evalation of nonglomerular hematuria, stone dz, and voiding d/o. Reserved for Pt. w/ nl renal fx as iodinated contrast dye has the potential to affect kidney function adversely.
Radionuclide scanning using technetium isotopes to assess the contribution of each kidney to the overall renal function. Important to know, if unilateral nephrectomy is planned for malignancy or living donation.
Routine dipstick is less sensitive to nonalbumin proteins and may not detect heavy and light immunoglobulin chains.
Renal scan is also useful in transplantation.
MRI and MRA is helpful in evaluating renal masses, detecting RAS, and diagnosing renal vein thrombosis. MRA needs gadolinium-based contrast agents, which are associated with development of nephrologenic fibrosing dermopathy in patients with advanced renal failure or dialysis dependence.
Non-contrast helical CT scanning has become the test of choice in evaluating nephrolithiasis.
Kidney biopsy to determine diagnoses, guide therapy, and prognosis in evaluation of glomerular or deposition disease.
Biopsy of renal transplant allograft: to distinguish acute rejection from medication toxicity.
Biopsy of a native kidney: unexplained proteinuria or hematuria. In SLE with the renal involvement, to help classify disease and guide therapy.
Shrunken fibrotic kidney biopsies is not useful and maybe dangerous for bleeding. Preoperative measures for native kidney biopsy include, US (to document the presence of two kidneys, assess size, and location), UA, urine culture to exclude infection, BP control, and correction of coagulation parameters. If uremic platelet dysfunction is suspected by an elevated bleeding time (>10 min) or abnormal platelet function assays, ddAVP, 0.3 mcg/kg IV in 30 min prior to Bx. ASA and other antiplatelet agents should be avoided for several days before and immediately after the biopsy. Patients on dialysis should not receive heparin immediately after the biopsy. CBC q6h, ON. Hb drop of approximately 10% is common postprocedurally. Difficulty voiding after the procedure may represent urethral clot obstructing the flow of urine.
Collected from "spot" urine sample.
FENa >1% with oliguria is almost always ATN, but can be prerenal with diuretics.
FENa <1% with oliguria is generally prerenal: suggestive of renal hypoperfusion with intact tubular function. Volume depletion, severe CHF, or nephrotic syndrome, NSAID or dye toxicity, sepsis, cyclosporine toxicity, acute GN, and HRS are some causes. Also calculate FEurea in nonoliguric renal failure.
[(UBUN x PCr) / UCr x PBUN)] x 100. Used in nonoliguric ARF and/or in Pts have been exposed to loop diuretics in the previous day.
Urine sodium, potassium, and chloride can be useful in evaluating acid-base disorders.
Uosm can be helpful in disorders home water handling (hyponatremia and hypernatremia)
FeUrea <35% is consistent with pre-renal etiology.
FeUrea >50% is consistent with renal (tubular) etiology.