Abstract
Background and Aims
Microscopic examination of urine sediment is a well-established and inexpensive technique for differential diagnosis of acute kidney injury. Especially renal tubular epithelial cells (RTEC) and granular casts (GC) have been shown to be a strong predictor of acute tubule necrosis (ATN), the assumed most common cause for AKI in cardiac surgery patients. So far, no study evaluated urine sediment before manifest AKI is evident. Therefore, the aim of this prospective trial was to evaluate if early changes of urine sediment parameters are indicative for development of acute kidney injury.
Method
Sequential urine sediment specimens were analyzed on day 0 (d0), day 1 (d1) and day 4 or 5 (d5) after cardiac surgery in n=37 patients. Urine analysis was conducted immediately after collection of urine specimens. Analysis includes detection of RTEC and GC as well as hyaline casts (HC), squamous epithelium (SE), erythrocyte count (EC) and leucocyte count (LC). Urine score (US) - consisting of RTEC and GC - which is described as indicative for ATN, was calculated as described previously. For detection of AKI, serum creatinine, serum cystatin c and urine output were recorded. Urine sediment changes over time were analyzed using differences between day of surgery (d0) and day 1 (d0-d1 = Δd1) or day 5 (d0-d5 = Δd5), respectively.
Results
Of the 37 included patients n=10 (27%) developed AKI within 5 days. According to the definition of KDIGO 2012, two patients developed Stage 1 (20%), six patients Stage 2 (60%) and two patients Stage 3 (20%) AKI. Median age was 67 years (IQR: 63.5-73.0). Mean HC, GC, RTEC and US tended to be higher in AKI patients from day one after surgery. Looking at the urine sediment changes over time (Median; IQR), Δd1 of RTEC (AKI: 0.65; 0.00 – 1.15 vs. No AKI: 0.00; -0.03 – 0.03; p=0.010), GC (AKI: 0.25; 0.00 – 0.50; No AKI: 0.00; -0.20 – 0.00; p=0.002) and US (AKI: 0.00; -0.25 – 0.00 vs. No AKI: 0.00; 0.00 – 1.00; p=0.047) were significant higher in AKI group. Also HC (AKI: 1.00; 0.00 – 1.00; No AKI: 0.00; -1.25 – 1.00; p>0.05) tended to be higher in AKI on Δd1, whereas SE, EC and LC did not show any trend between both groups. Δd5 did not show any significant result between AKI and non-AKI. Because all of these patients were catheterised, the results on urinary erythrocyte count were interpreted with appropriate caution.
Conclusion
This is the first study evaluating sequential urine sediment measurements for early detection of AKI in cardiac surgery. According to these preliminary data, Δd1 of RTEC, GC and US is significant higher in AKI, suggesting that an increase from day of surgery to day 1 may be indicative for the development of AKI right before manifest AKI is evident. Therefore sequential urine sediment measurements could be useful for early detection of AKI after cardiac surgery.
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