What was the revenue growth rate for the process-driven business in the third quarter of 2019 compared to the same period in the previous year 
 I think like everybody else, we'd also put out the caveat that we are closely watching the geopolitical situation. And impact of tariffs, which have been so far modest in our exposure, but we keep an eye on that for the long term and any changes. So we're cautiously optimistic as we look forward in China.
Brandon Couillard -- Jefferies -- Analyst
Okay. And then maybe one follow-up for Annette. We'd love to get an update on the cell analysis portfolio, and specifically any interest you're seeing in the ZE5 cell imager? Thanks.
Annette Tumolo -- Executive Vice President, President, Life Science Group
Well, you know, I think we're seeing good demand in our flow analysis products. And with respect to the ZE5, we see a lot of traction in pharma and biopharma due to the particular feature set and value proposition, it offers to those customers.
Brandon Couillard -- Jefferies -- Analyst
All right. Maybe one for Norman, just to round out here. Cash continues to build pretty substantially on the balance sheet. The buyback is relatively immaterial in the third quarter. Just give us a sense perhaps why the buyback doesn't seem to be a higher priority, and kind of your current view on the M&A pipeline, and whether or not you might be any closer to finding something attractive out there? Thanks.
John Hertia -- Executive Vice President, President, Clinical Diagnostics Group
So Brandon, [Speech Overlap]
Norman Schwartz -- Chairman of the Board, President and Chief Executive Officer
Yes. It's always...
John Hertia -- Executive Vice President, President, Clinical Diagnostics Group
Go ahead, Norman.
Norman Schwartz -- Chairman of the Board, President and Chief Executive Officer
...yes. I -- yes, I've got that. I think that -- you know, it's always a balance. You got opportunities that you're looking at and -- so you know, you -- it's -- we try to keep the cash for those, but nevertheless we did get in the market and did buyback some shares during the quarter. So again it's a balance between saving it for the right acquisition and the buyback. So we're trying to manage it the best we can.
Brandon Couillard -- Jefferies -- Analyst
All right. Thank you.
John Hertia -- Executive Vice President, President, Clinical Diagnostics Group
Thank you.
Operator
We have a follow-up question from the line of Jack Meehan with Barclays. Your line is now open.
Jack Meehan -- Barclays -- Analyst
Thanks. Maybe just to start on the process-driven [Phonetic] business. I know that was up modestly year-over-year. I think previously, you're assuming some modest level of growth, back half over back half is that still the implied assumption for the fourth quarter?
Ilan Daskal -- Executive Vice President and Chief Financial Officer
So Jack, thanks for the question. The answer -- the short answer is, yes. I mean we still project the incremental growth to be this year. So obviously, most of the growth we projected in Q4.
Jack Meehan -- Barclays -- Analyst
Okay. And then the gross margin of 56% was really strong 250 bps year-over-year. Was there anything to call out in terms of some of the efficiency initiatives or mix of consumable versus instrument, which might help that progression in the quarter?
Ilan Daskal -- Executive Vice President and Chief Financial Officer
Yes. A great question. Thanks, Jack. There is -- obviously, the mix with more consumables in this quarter relative to Q3 of 2018, that was definitely one major component there. And two other items that I would highlight will be the lower inventory reserves and the lower logistics cost. These are two items that we called out last year at the same time. And these are definitely items -- areas that we improved and that contributed to the incremental gross margin this quarter.
Jack Meehan -- Barclays -- Analyst
Great. And maybe, Andy, I know you mentioned you're not giving 2020 guidance at this point. But at the last Analyst Day in November 2017, you had the 20% target. Just given the progression you've had the last few years and the trajectory year-to-date, I mean, does that still feel pretty doable?
Andrew L
 I think like everybody else, we'd also put out the caveat that we are closely watching the geopolitical situation. And impact of tariffs, which have been so far modest in our exposure, but we keep an eye on that for the long term and any changes. So we're cautiously optimistic as we look forward in China.
Brandon Couillard -- Jefferies -- Analyst
Okay. And then maybe one follow-up for Annette. We'd love to get an update on the cell analysis portfolio, and specifically any interest you're seeing in the ZE5 cell imager? Thanks.
Annette Tumolo -- Executive Vice President, President, Life Science Group
Well, you know, I think we're seeing good demand in our flow analysis products. And with respect to the ZE5, we see a lot of traction in pharma and biopharma due to the particular feature set and value proposition, it offers to those customers.
Brandon Couillard -- Jefferies -- Analyst
All right. Maybe one for Norman, just to round out here. Cash continues to build pretty substantially on the balance sheet. The buyback is relatively immaterial in the third quarter. Just give us a sense perhaps why the buyback doesn't seem to be a higher priority, and kind of your current view on the M&A pipeline, and whether or not you might be any closer to finding something attractive out there? Thanks.
John Hertia -- Executive Vice President, President, Clinical Diagnostics Group
So Brandon, [Speech Overlap]
Norman Schwartz -- Chairman of the Board, President and Chief Executive Officer
Yes. It's always...
John Hertia -- Executive Vice President, President, Clinical Diagnostics Group
Go ahead, Norman.
Norman Schwartz -- Chairman of the Board, President and Chief Executive Officer
...yes. I -- yes, I've got that. I think that -- you know, it's always a balance. You got opportunities that you're looking at and -- so you know, you -- it's -- we try to keep the cash for those, but nevertheless we did get in the market and did buyback some shares during the quarter. So again it's a balance between saving it for the right acquisition and the buyback. So we're trying to manage it the best we can.
Brandon Couillard -- Jefferies -- Analyst
All right. Thank you.
John Hertia -- Executive Vice President, President, Clinical Diagnostics Group
Thank you.
Operator
 We have a follow-up question from the line of Jack Meehan with Barclays. Your line is now open.
Jack Meehan -- Barclays -- Analyst
Thanks. Maybe just to start on the process-driven [Phonetic] business. I know that was up modestly year-over-year. I think previously, you're assuming some modest level of growth, back half over back half is that still the implied assumption for the fourth quarter?
Ilan Daskal -- Executive Vice President and Chief Financial Officer
So Jack, thanks for the question. The answer -- the short answer is, yes. I mean we still project the incremental growth to be this year. So obviously, most of the growth we projected in Q4.
Jack Meehan -- Barclays -- Analyst
Okay. And then the gross margin of 56% was really strong 250 bps year-over-year. Was there anything to call out in terms of some of the efficiency initiatives or mix of consumable versus instrument, which might help that progression in the quarter?
Ilan Daskal -- Executive Vice President and Chief Financial Officer
Yes. A great question. Thanks, Jack. There is -- obviously, the mix with more consumables in this quarter relative to Q3 of 2018, that was definitely one major component there. And two other items that I would highlight will be the lower inventory reserves and the lower logistics cost. These are two items that we called out last year at the same time. And these are definitely items -- areas that we improved and that contributed to the incremental gross margin this quarter.
Jack Meehan -- Barclays -- Analyst
Great. And maybe, Andy, I know you mentioned you're not giving 2020 guidance at this point. But at the last Analyst Day in November 2017, you had the 20% target. Just given the progression you've had the last few years and the trajectory year-to-date, I mean, does that still feel pretty doable?
Andrew L