How do you diagnose acute kidney injury in a pregnant patient?
Acute kidney injury (AKI) is a rare but serious complication of pregnancy. The diagnosis of AKI in pregnancy is the same as in nonpregnant patients. Due to the physiologic increase in GFR during pregnancy, normal serum creatinine level during pregnancy range from 0.4– 0.8mg/dl range, although “normal values” are not specifically defined for pregnancy.
There is no published data on the accuracy of GFR formulas (including CKD-EPI and MDRD formulas) in pregnancy. Both formulas underestimate GFR as measured by inulin clearance by 40%.
What tests to perform?
Laboratory studies are performed to assess renal function, electrolytes, hemoglobin, hematocrit, platelet count, and coagulation profile. Urine sediment analysis is also an important part of the evaluation of AKI. A 24-hour urine collection for total protein quantification and creatinine clearance should be considered as part of the work up especially in patients with suspected preeclampsia.
Ultrasound should be considered in women with AKI, however true obstruction may be difficult to differentiate from physiologic hydronephrosis of pregnancy, especially near term. MRI can help distinguish physiologic hydronephrosis from obstruction in pregnancy.
What are the causes of acute kidney injury in pregnancy?
Pre-renal causes of AKI during pregnancy
Antepartum hemorrhage due to placenta previa, placenta accreta or abruptio placenta
Postpartum hemorrhage due to atonic uterus or uterine rupture
Excessive vomiting due to hyperemesis gravidarum
Sepsis due to chorioamioninitis, retained products of conception or septic abortion
Intrinsic renal causes of AKI during pregnancy
Acute tubular necrosis (ATN) secondary to prolonged hypotension in the setting of antepartum or postpartum hemorrhage, sepsis, drugs (aminoglycosides used for treatment of chorioamnioniits), acute fatty liver disease of pregnancy.
Cortical necrosis – the most extreme form of hemodynamic renal injury in pregnancy
Glomerulonephritis: Lupus nephritis, IgA nephropathy, post-infectious glomerulonephritis
Thrombotic microangiopathies including TTP and atypical HUS. HUS is most likely to develop in the peri-partum period.
Post-renal causes of AKI during pregnancy
Renal pelvis obstruction: renal stones, papillary necrosis
Ureteric obstruction: renal stones, surgical ligation of ureters, cervical cancer
Urethral obstruction: blood clots, kinked urinary bladder catheter
Hydronephrosis of pregnancy is caused by ureteral dilatation from hormone-induced smooth muscle relaxation and mechanical pressure of the gravid uterus. Risk factors for obstructive uropathy from ureteral compression include twin pregnancy, polyhydramnios, pyelonephritis and renal calculi.
How should patients with acute kidney injury in pregnancy be managed?
The most important step in the management of AKI in pregnancy is making the correct diagnosis as many conditions have overlapping features, such as preeclampsia/HELLP, lupus nephritis, TTP/HUS and acute fatty liver of pregnancy. Management strategies vary dramatically based on etiology.
AKI secondary to preeclampsia, HELLP syndrome or other obstetric conditions usually represents a catastrophic complication of pregnancy and necessitates delivery of the fetus.
Management of ATN remains supportive: restore intravascular volume, avoid nephrotoxins, provide dialytic support as indicated.
Glomerulonephritis flares are often treated with steroids or other pregnancy-safe immunosuppression (calcinurin-inhibitors)
Thrombotic microangiopathies should be treated with plasma exchange (TTP) or complement pathway inhibition (atypical HUS).
Dialysis should be initiated for similar reasons as in the nonpregnant population. However, BUN is fetotoxic – in pregnancy dialysis should be considered when BUN values rise above 50 mg/dL in addition to conventional indications.
How to utilize team care?
Management of these patients should be in conjunction with the nephrology and obstetrics team.
Are there clinical practice guidelines to inform decision making?
In high-resource settings, AKI rates are low (2-3/10,000 births) but incidence has been slowly rising due increasing maternal age and maternal comorbidities.
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- How do you diagnose acute kidney injury in a pregnant patient?
- What tests to perform?
- What are the causes of acute kidney injury in pregnancy?
- How should patients with acute kidney injury in pregnancy be managed?
- How to utilize team care?
- Are there clinical practice guidelines to inform decision making?
- Other considerations