We use FITC-inulin clearance in our lab, however in the clinical setting, I would assume that determining creatinine levels in the plasma might be useful to estimate GFR, however this method can be cumbersome.

The best method probably depends on the context: if the purpose of measurement is a study the inulin method by the constant infusion technique with plasma measurements (see for example Montanari A et al., Am J Physiol 2012; 303:648) could be a good option. In the daily clinical practice, short periods of creatinine clearance calculation (even 2 hour- periods of clearance, in patients with bladder catheter, see Herrera-Gutierrez ME et al., Int Care Med 2007; 33:1900) can be used. Creatinine to estimate GFR in ICU patients by formulas (mainly developed for CKD) can be used only if renal function is stable, (i.e. serum creatinine is not changing along a 48 hour period).

Thank you both for your answers and for the references. I've just published on 4h creatinine clearance in the ICU (Pickering JW, et al Crit Care 2012;16(3):R107), which was a post-hoc analysis of a broader study. The next step is to compare this with an inulin clearance (not sure why I typed insulin above :)). Having the opinions of people who have done similar measures in the past helps. I'm hoping, with a bit of math, to be able to account for some of the unstable renal function issues.

Hallo, I could measure both glomerular filtration and barrier functions in Zebra fish, i measure them quantitatively and qualitatively after Dextran injection,., Dextran has different sizes...

As the clinical state of the hospitalized patients, especially those in the intensive care unit is not stable and changes daily. The eGFR is not recommended in such circumstances as there will be great variations and should not be used in such circumstances in clinical practice, unless it is part of a study.

Absolutly the iohexole clearance determined only by blood only determination

This is really a tough topic. We beleive there is no good method at this point because the exact ones are not useful in clinical practice (iohexole or inulin) and the rest are inexact. For the everyday practice (follow-up of kidney function) we use AKIN stratification but when interested in a more exact evaluation (mainly to know when to wean from RRT, to know renal function when in urine is recovered after AKI or to dose sensible drugs in these patients) we use short-time urine collection for creatinine clearance claculation. We look forward to evaluate and test the new mechanized method for inulin measurement so we'll be glad to hear results from Dr Pickering soon...

Regarding stimates as CKPD..., we only use Cockroft as the other ones (in our centre) did nor result in good stimations but in fact do not relish much in these equations because measurement is easy when short-time is used. Cistatin was not really interesting in our view because added not much to creatrinine with a sensibly higher cost.

Gracias Manuel

Nice to be in contact. I'm aware of your v interesting 2007 study of 2h clearance compared with 24h clearance. Do you use 2h clearances still? If you've data comparing 2h creatinine clearance with inulin it would be well worth publishing. Unfortunately for us because of funding we are not able to do the follow-up of inulin clearances compared with 4h creatinine clearance. I'm hoping someone else does it sometime soon.

In the meantime we've continued to analyse data we have and discovered an "anomaly" with creatinine following cardiac arrest in that it the concentrations reduced by as much as 50% in some cases. Far more than could be explained by dilution due to fluid loading. We hypothesise that cardiac arrest resulted in a temporary loss of creatinine production (Crit Care 2013 vol. 17 (1) p. R7). Really hard to prove that as I know of no direct measure of creatinine production. Probably another nail in the coffin of relying on creatinine alone. Urine output alone as a marker of AKI is another interesting area - we recently found that a rate of 0.3 to 0.5 ml/kg/h for 6 hours made no difference to mortality or dialysis outcomes, whereas only

Gracias a ti.

Really challenging. In effect, we still attach to creatinine clearance. In other scenarios (sepsis) we have tested cistatiC and NGal without impressive results and are now preparing a short try with nephrocheck. We would like to test inulin but lack funds as well... Your idea about cardiac arrest is really interesting (and with other implications as could be the behavior under severe hypothermia...). By the way we found your paper in diuresis really interesting.

It is a difficult field and with so many open fronts. Our next challenge will be to (try to) ) prepare a protocol to test renal reserve in patients recovering from AKI but it is difficult, I don´t see clearly the best approach and follow-up must be long-timed so it is still a very-very early project.

We look forward to read from you soon.

Renal reserve in AKI sounds very interesting. If I may speculate it may be the loss of renal reserve following AKI that leads to increased risk of developing CKD.

I've been in touch with John Prowle recently who is doing some interesting work with urine output - worth keeping an eye out for. Also the following just appeared in CJASN online:

Leedahl, D. D., Frazee, E. N., Schramm, G. E., Dierkhising, R. A., Bergstralh, E. J., Chawla, L. S., & Kashani, K. B. (2014). Derivation of Urine Output Thresholds That Identify a Very High Risk of AKI in Patients with Septic Shock. Clinical Journal of the American Society of Nephrology. doi:10.2215/CJN.09360913

They found that as little as 3 hours of consecutive oliguria was associated with adverse outcomes.

I'll look after this paper. I agree this is an interesting aproach even when I am somewhat cautious because the posibility of overdiagnosing AKI. Anyway, the most important aproach right now (as I see it) is the early awareness of the impendiing problem and in this aspect your results and tjhe one from Prowle are a step ahead and I'll emphatice them among my colleages and in our future protocols.

Hope we´ll keep in contact.